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Flashcards

Evolution and Genetics Part 1

Daniel Kirkbride Psychology Inglês 200 flashcards

Evolution and Genetics Part 1

Flashcards do conjunto (200)

  1. 1The Problem of HistoryOrganisms has many differences but also significant commonalities (e.g. pattern of bone structure in vertebrate limbs).
    Protein chains often have the same order across species (e.g. monkeys and fish share 82/104 of cytochrome c order).
    Possible to group species hierarchically based on shared structures - more divergence the farther you go.
    Common ancestors explain the problem of history (where all the species of animal came from) through gradual modification. Phylogenies (family trees) go back more deeply for less-related species.
  2. 2The Problem of DesignOrganisms adapted to suit the environment (e.g. camouflage). Often very complex e.g. echolocation involves rapidly turning hearing on and off (problem of design). Some structures have no purpose (vestigial structures) such as a pelvis in whales. Too sophisticated to be due to chance. Religious theories do not explain vestigial structures. Useful changes more likely to be retained and vestigial structures gradually lost.
  3. 3Homologies and AnalogiesHomologies: Similarities between organisms due to common ancestry. Reflect history and useful for constructing phylogenies.
    Analogies: Similarities due to parallel selective pressure/convergent evolution (equinfinalilty) and similar requirements for survival.
  4. 4The Modern SynthesisDarwin did not know how traits were passed on. Originally believed that traits were blended. Mendel's work explain this and was combined with Darwin's in the modern synthesis.
  5. 5Evidence for Evolution: Galapagos Finches (Grant)Several different types of finch on the island with many homologies and local divergence. Researchers could measure whole population of medium ground finches due to small numbers.
    Variation in beak size (heritable) where big beaks can eat larger/harder seeds.
    1977 drought led to less available small/soft seeds. Big beaks increase survival. After drought average beak size was larger due to big-beaked hatchlings. If drought had continued, calculated that the medium ground finch would become the large ground finch in 46 years.
  6. 6Reasons for 'Gaps' in the Evolutionary RecordGaps are due to lack of preservation of remains (fossilisation is extremely rare). Common intermediate between humans and apes is Sahelanthropus (6-7m years ago), then Australopithecus and then genus Homo.
    Homologies also show proof for evolution.
    Fossils explain vesitigial structures, e.g. vestigial pelvis of the whale comes from Ambulocetus (had hind legs) and Basilosaurus (tiny hind legs possibly for grasping).
  7. 7Explaining Present Day Behaviour: Nausea and Vomiting of PrenancyPregnant women develop aversions to foods and cravings for others. Thought to be an evolutionary adaptation to prevent food poisoning. Mother and embryo are most vulnerable during the first trimester (where NVP appears) and is usually directed to foods most likely to contain dangerous toxins (meat, animal products) and divert to safe alternatives (fruits, sugars, grains).
    Study of 22,000 pregnancies - NVP reduced miscarriage rate sharply.
  8. 8Definitions: Phenotype and Genotype Eukaryote and Prokaryote Diploid and Haploid• Phenotype: Observable characteristics of an individual (hair colour, blood type).
    • Genotype: Unobservable, heritable characteristics.
    • Eukaryote: Plant and animal cells. Have a nucleus and mitochondria.
    • Prokaryote: Bacteria. Similar components to eukaryotes but with a different.
    • Diploid: Organisms with 2 copies of each gene.
    • Haploid: Organisms with 1 copy of each gene.
  9. 9Cell StructureAnimals cells share many common structures despite specialisation.
    Ribosomes synthesise substances needed for cell function.
    Mitochondria break down glucose for energy.
    Made of chemical compounds, mostly proteins (12% of body weight; give cells structure; make connecting tissues; work as antibodies, hormones and enzymes). Proteins are chains of amino acids and the order determines properties.
    Phenotypic variation is caused by variants of the same type of protein and amino acids due to differences in DNA bases.
  10. 10Principles of Classical Genetics1. 'Particles of inheritance' (genes) are passed from parents to offspring which determines phenotype.
    2. Genes come in alternate forms (alleles) which is the part that varies (everyone has the same genes but different alleles) due to base order in DNA. Can be denoted using upper and lowercase (A and a) or numbered (a1 a2 a3).
    3. In a sexually reproducing species, individuals have 2 copies of each gene, one from each parent.
  11. 11Functions of Genes and The Central Dogma2 functions of genes: to influence physical characteristics (genotype influences phenotype - function a) and to replicate themselves to produce cells with the same genotype (function b).
    The central dogma - genes affect proteins but proteins don't affect genes. Phenotype cannot influence genotype.
  12. 12Somatic and Germ Cell LinesSomatic cells make up most of the body and can only make more of the current phenotype (e.g. skin cells). Reproduce through mitosis (split into identical copies).
    Germ cells (gametes) make more genotypes and are produced through meiosis.
  13. 13Properties of DNA and BasesDNA winds round histone proteins. At various points in its life, DNA will assemble into linear chromosomes (Diploids have 23 pairs which are similar).
    DNA is a polymer (long-chain molecule) and consists of the sense and anti-sense strands bound to each other and twisted around a double helix. Backbone of sugar phosphate and 4 bases (ACGT) occurring in any order.
    Bonds in each strand are very strong but they are weak between strands.
    As pair with Ts and Cs with Gs.
  14. 14DNA: Self-Replication, Transcription and TranslationCan complete function b (self-replication) when two strands are split in the right conditions. Free-floating As will join with free-floating Ts and Cs with Gs to make a new strand.
    Can complete function a (making phenotypes) through transcription. When strands are split in different conditions, messenger RNA forms along the anti-sense strand. RNA is similar to DNA but T is replaced by U.
    RNA creates a negative copy of the DNA sequence (transcription) and when formed, separates from the DNA (which closes itself) and is transported to ribosomes to build protein chains (translation).
  15. 15Codons, Genetic Code and Substitutions4 bases make 20 amino acids by coming together to make a triplet of bases that code for an amino acid (known as codons). Mapping of codons in mRNA to amino acid is called genetic code.
    64 possible codons, so some make the same amino acid.
    Synonymous substitutions are changes in sequence that make no difference (e.g. CCA to CCC). Errors in transcription often make little difference. 3rd base changes often cause no change and 1st base changes make a similar acid.
  16. 16Genomics - Non-Coding DNAHuman genome has 6.4 billion base pairs across 23 chromosome pairs. Recently discovered that genes only take up a small fraction of the genome.
    About 25,000 genes with average length of 27,000 base pairs, though 60% of genes are not transcribed (known as non-coding DNA).
    Within a gene, not even all bases code for proteins. Exons are codons that get translated into protein, introns are transcribed but deleted from mRNA and not translated (non-coding). Much more introns than exons meaning average coding length is only 1,340 base pairs.
  17. 17Pseudogenes and Transposable ElementsSome non-coded DNA thought to be remains of sequences no longer used (pseudogenes), thought to be vestigial, though most non-coding DNA is not pseudogenic and about 43% of the genome consists of multiple near-identical copies of a particular sequence (transposable elements). TEs can copy themselves into different parts of the genome over evolution.
  18. 18Simple Sequence Repeats and Functions of Non-Coding SequencesSSRs - shorter sequences that are internally repetitive. Very prone to mutations which increase or decrease number of repetitions.
    Some non-coding sequences are identical across many organisms, suggesting an unknown, naturally selected function.
    More than coding genes are transcribed into RNA, some non-coding genes are thought to have regulatory functions for transcription and translation.
  19. 19Purpose of Repetitive DNARepetitive DNA may enhance evolvability. SSRs provide small changes in gene products over generations and TEs promote reshuffling of genetic material in meiosis, as well as moving parts of genetic sequence about the genome.
  20. 20Phenotypic Complexity and Number of Genes/DNAAmount of DNA in different organisms varies greatly and cannot be explained by phenotypic complexity. Polyploidy (having more than 2 copies of the genome) cannot even explain all cases.
    Number of genes tends to rise with phenotypic complexity but the rise is slower than that of DNA. Complex phenotypes may require more regulatory sequences, explaining rise of introns in complex organisms.
  21. 21Parasites in DNATEs could be considered parasites as they may be functionless but still aim to replicate themselves. Example of parasite is HIV - a human endogenous retrovirus that copies itself into the host's DNA.
    Parasitic sequences may have some cost but it may be so small that it is not uncovered by selection for many years.
    Parasites do better in complex organisms like mammals as they have smaller populations (than bacteria) which are less efficient at selection.
  22. 22Mitochondrial DNAMitochondria also have some of the human genome, 16,500 base pairs. Widely accepted that this is because the mitochondria was previously a separate bacterial organism that later incorporated into eukaryotic cells.
    Mitochondrial DNA has special features, mutates quickly and is haploid as it is only passed through the maternal line in eggs.
  23. 23Definitions: Locus Polymorphism• Locus: A particular site in the genome.
    • Polymorphism: A locus where there is more than 1 allele for a trait in the population (e.g. hair colour).
  24. 24Meiosis and RecombinationGametes can only have 1 set of chromosomes so that when they combine at fertilisation, the 2 sets make 46 chromosomes. Happens through meiosis.
    Progenitor cell (cell making the gametes) has one copy of chromosomes from each parent and it is random which chromosome is chosen with equal odds. Chromosomes also chosen independently of one another.
    Sometimes paired chromosomes will exchange DNA (recombination). Occurs at every gamete formation so the outcome of every recombination is different.
  25. 25Meiosis and Genetic LinkageChromosomes segregate independently, meaning genes on separate chromosomes also do this. Genes on the same chromosome will be transmitted together (Genetic Linkage).
    This can only be disrupted by recombination. Linkage and likelihood of recombination is influenced by how close the two genes are on the chromosome.
  26. 26Mutations - Single-Base SubstitutionsMutations are the ultimate origin of variation.
    Substitution of one base pair to another, usually a copying error.
    Changes between C & T, and A & G (chemically similar) are transitions. Changes between dissimilar bases (e.g. C to A/G) are transversions.
    Base deletion can also occur but it less frequent. Rate of mutation is higher when C follows G in the sequence.
    Only a 1 in 4m chance of substitution but every individual will carry some changes due to large volume of the genome.
  27. 27Mutations - Simple Sequence Repeat Expansions and ContractionsLarger and more common. And extra copy of a simple sequence repeat is added or lost when the RNA bonds to the wrong repeat.
    Rate of 1 in 1000 per locus per generation.
  28. 28Mutations - Transposable Element InsertionInvolves a TE copying itself from one part of the genome to another. Can be just between many base pairs or from one chromosome to another.
    Occurs once in every 10-100 births and may have a phenotypic effect if it disrupts the coding for a protein.
  29. 29Mutations - Segmental DuplicationsWhere a chunk of sequence copies itself during replication (deletions and inversions can also occur).
    SDs thought to be significant in evolutionary change. Once a gene is evolved to serve a purpose, selection keeps it the same as mutants are unlikely to be better. Having 2 copies of a gene means the second copy can form new mutations and functions without taking away from the organism (can create new genes).
    Humans often belong to gene families (multiple genes descending from a common ancestor through duplication). Members in a gene family make similar products with subtle functional differences.
    Sometimes an SD can happen to an entire chromosome (trisomy) e.g. Down's Syndrome.
  30. 30Mutations - Whole-Genome DuplicationVery rare. The whole genome can duplicate itself, meaning one has 4 copies as opposed to 2. Acts like a huge SD.
    Accounts for polyploidy in plants and amphibians and can contribute to the origins of gene families.
  31. 31Genetic DiversityProbabilities of mutation mean each individual likely has a new mutation.
    1 in every 1000 bases will vary from individual to individual (known as single nucleotide polymorphism).
    SSRs very polymorphic due to high mutation rate, meaning everyone is unique (also the basis of DNA fingerprinting).
    12% of human genome consists of sequences due to SDs.
  32. 32Effects of MutationsMost genetic variation has no effect on phenotype as it happens in non-coding DNA. Polymorphisms in exons may make no difference due to redundancy of genetic code.
    Most mutations that do have a phenotypic effect will be deleterious (e.g. genetic diseases). Mutation is undirected and unrelated to needs and functions of the phenotype. Undirected modification of the well-functioning phenotype is unlikely to cause improvement, though if a mutation improves the phenotype it will be spread by selection.
  33. 33How Genotypic Variation Leads to Phenotypic VariationDNA sequence change creates a distinct allele, which is transcribed and translated to produce a different amino acid/protein.
    New protein will either be integral to a body system, making it differ from the usual, or will act as an enzyme that catalyses another bodily reaction, leading to a different phenotype.
  34. 34Single-Gene CharacteristicsMost genes have many functions and most functions are a result of many genes. Single-gene characteristics are a difference in phenotype determined by a differing allele at just one locus, e.g. Mendelian diseases (like cystic fibrosis) and blood type.
  35. 35Gene Hunting - Linkage StudiesExamine a large family with multiple members having a characteristic and establish the genotype for each member at marker loci (chromosomal locations). Search data for marker alleles shared by affected family members but not by unaffected members. Useful when looking for single-gene characteristics using a small number of markers.
  36. 36Gene Hunting - Association StudiesUse large groups of individuals with and without a characteristic to compare frequency of different alleles. Powerful but require hundreds of markers per chromosome. Two Approaches:
    1. Candidate gene approach - focuses in on a few genes where prior research suggests involvement in the trait.
    2. Genome-wide approach - covers the entire genome using thousands of marker loci. Easier now with technological advances.
  37. 37Identifying Alleles for Polygenic TraitsPolygenic traits have multiple alleles involved, meaning there is lots of room for genetic variation and trait is normally distributed. Some individuals with the same characteristic (e.g. average height) may share no alleles as there are so many (e.g. ABCdef and abcDEF).
    Polygenic characteristic genes are much harder to detect in gene hunting studies because of this. Requires much larger samples to be reliable.
  38. 38Genes for Physical Characteristics - Huntington's DiseaseAn incurable Mendelian disease causing gradual loss of coordination and cognitive ability. Caused by an allele on chromosome 4 which codes for Huntingtin (active in the CNS).
    Gene contains a SSR of CAG (glutamine), normal copies have 11-34 copies. Disease allele has over 40 copies, leading to different reactive properties in the strain meaning neurons do not survive as well, causing symptoms.
  39. 39Genes for BehaviourGenotypic changes can change behaviour as all behaviour has neural underlying mechanisms, making behaviour part of the phenotype.
    This can affect long-term mating (Young et al.) and mood regulation in the MAOA gene (Brunner et al.).
  40. 40Definitions: Heredity Homozygous Heterozygous• Heredity: Offspring resemble their parents.
    • Homozygous: Having 2 copies of the same allele.
    • Heterozygous: Having different copies of 2 alleles.
  41. 41Mendelian GeneticsOriginal paper was rejected until the 1930s.
    First generation (F1) of hand-pollinated pea plants were all yellow and not green. Second generation (F2) were 75% yellow 25% green, suggests heredity is not a blending process.
    Assumed that each individual carries 2 genes to lead to either result (yellow or green). Possible outcomes can be worked out in Punnett squares.
    Genetic material is passed on in all diploid, sexual organisms. 50-50 chance of inheriting each gene in plant breeding.
  42. 42Determining Dominant and Recessive AllelesGenes often code for enzymes. As long as some of the enzyme is present it is enough to produce the phenotype (dominant).
    Recessive alleles cannot make the enzyme and so only causes effects when homozygous (e.g. albinism).
    Co-dominance can occur when heterozygous alleles are equally dominant (e.g. blood type AB).
    Incomplete dominance is where the phenotype is an intermediate form of the 2 alleles (e.g. pink carnations from red and white parents). Not the same as blending as the alleles are still separate.
  43. 43Independent SegregationGenes segregate independently (e.g. pod colour does not influence texture).
    This means novel phenotypic combinations can arise from sexual reproduction.
    Natural selection can also change frequency of characteristics without changing that of others (i.e. focusing only on an adaptive quality).
    Independent segregation occurs during meiosis.
  44. 44Mendelian DiseasesSerious disease are very rare as sufferers tend to die before reproducing. 2 ways a disease can survive:
    1. Dominant lethal genes (e.g. Huntington's) only have phenotypic effects after reproduction occurs (starts in later life).
    2. Disease alleles may be recessive so heterozygotes can be carriers (e.g. haemophilia).
    Lethal recessives are a reason not to inbreed as having a homozygous child is more likely.
  45. 45Allele Frequency and the Hardy-Weinberg Theorem.Explains how a genotype will be distributed over generations.
    Frequency of genotypes is p^2, 2pq, q^2 with p being frequency of the dominant and q being frequency of the recessive.
    HWT allows us to see frequency of a trait no matter the likelihood of gaining each allele.
    Recessive alleles can still have equal chance of occurring with the right frequencies.
  46. 46Genetic DriftHWT is limited as it models an infinite population size (larger populations will have more similar outcomes to the model).
    Genetic drift - the concept that smaller populations will have more dramatic fluctuations in allele frequency over generations.
    GD is important for evolution as allele frequencies fluctuate a little over generations even when they have no phenotypic effect.
    Occasionally new mutations fluctuate until fixation but the probability of this is 1/2N (N being population size).
  47. 47Neutral Theory and the Molecular ClockNeutral theory - Two populations that are isolated from one another will diverge over time in their DNA due to neutral fixations caused by genetic drift.
    Rate of divergence is not dependent on size as fixation is more likely in small populations but new mutations are also more common (the two cancel out).
    Molecular clock - neutral changes occur at an approximately constant rate, so molecular divergence can be used to estimate the date of divergence and family trees between lineages (more different non-coding DNA means an older common ancestor).
    NT and MC can be used within and across species to track evolutionary descent.
  48. 48Quantitative GeneticsInvestigates continuously variable traits (e.g. height, IQ) with many genetic loci. Difficult to isolate genes locus by locus when using traditional experiments.
    QG investigates relationships in genotypic and phenotypic similarity.
    Some phenotypic variance is environmental (e.g. nutrition) and some genetic.
    Relies on the fact that close relatives share more genetic material than distant relatives. Genotype is important if the phenotype is more similar in close relatives than distant relatives or strangers.
  49. 49Estimating HeritabilityResemblance to relatives can be calculated by calculating phenotypic correlations (e.g. father-son height).
    Heritability (h^2) - the proportion of observed phenotypic variation that is accounted for by genetic variation.
    To estimate heritability, calculate how much variation in the trait is due to one parent's genes, then double it for both parents.
    Estimates assume all correlation is due to shared genetics as opposed to shared environment (e.g. affluent = tall kids), may be overestimating genetic contributions.
  50. 50Coefficient of RelatednessKnown as 'r', the probability that any allele in relative A is identical by descent to relative B. r for each parent is 1/2 (each gives half the genetic material), and 1/2 for each sibling (each parent contributes 1/4) and 1/4 for half-siblings.
    r is a measure of how much more similarity there is between relatives than there is between strangers (i.e. it increases frequency to above that of the population e.g. 0.7 to 0.9).
  51. 51Twin Studies and ACE ModelsMost estimates use twin studies (species without twin births are studied using full and half siblings).
    MZ and DZ twins share an environment and have a non-shared environment (e.g. disease, accidents). r in MZ = 1, in DZ = 0.5. Any difference in phenotypic correlation is due to the extra 0.5.
    ACE models measure heritability (A/G), shared environment (C) and non-shared environment (E). Allows quantification of the 3 determinants.
    Typical pattern of twin studies is that A is almost always much greater than 0 and C is less important than E.
  52. 52How to Measure A, C and EA: Falconer's estimate of heritability:
    2 x (MZ correlation - DZ correlation)
    C: MZ correlation - heritability (A)
    E: 1 - MZ correlation
  53. 53Adoption StudiesAdoption = one set of parents provide genetic and another provide environment.
    Correlations between adopted children and biological/social parents show strength of A and C. Can also investigate biological siblings adopted into different households and unrelated adoptive siblings.
  54. 54Issues with Twin StudiesStudies assume equal shared environment for MZ and DZ twins while studies show MZ twins are treated more similarly, though studies of MZ twins reared apart or together always show greater MZ influence and even when zygosity is mistaken MZ twins are more similar (Munsinger & Douglass).
    2/3 of MZ twins share a placenta meaning there is more shared environment, though this leads to competition, usually with unequal results and dissimilar birth weight. So environment may be less similar for MZ than thought.
  55. 55Issues with Adoption StudiesSelective placement of children (children are only adopted into good homes) meaning there is more likely to be a greater shared environment.
    Adoption agencies may also place children in homes similar to the birth family or to the child, meaning C is inflated (though most studies show C is unimportant so this is a small issue).
    Prenatal environment of the child is provided by the biological mother, meaning C is underestimated (resolve by correlating child with father phenotypes).
  56. 56Issues with ACE ModelsAssume that genetic effects are additive and so MZ twin genes have twice the genetic effect than DZ. This is not the case, e.g. homozygous recessive genes require 2 copies to take effect so having r=1 is more/less than twice the effect of r = 0.5.
    Relationship between genetic and phenotype similarity non-linear due to non-additive effects.
    Most studies still use ACE models as they are interested in A (additive genetic effects a.k.a. narrow-sense heritabilities).
  57. 57Dominance and Epistasis ModelsDominance effects: effects that happen due to the interactions between a pair of alleles at the SAME locus.
    Epistatic effects: effects that happen due to interactions between alleles at DIFFERENT loci.
    Estimates of heritability using dominance and epistasis are called broad-sense heritabilities.
  58. 58Heritability vs Genetic DeterminationHeritability is not genetic determination. 100% of variation in arm number is environmental but limb development is genetically determined.
    Reading is not genetically determined but ability is heritable (Stromswold).
  59. 59Heritability and Environmental VariationHeritability is specific to particular environments and can fluctuate as environment changes. Heritability does not explain population differences and cannot predict effects of environmental change.
    E.g. uniform soil quality makes difference in height very heritable, but non-uniform soil quality makes environmental factors more influential.
    Some geneticists prefer to use coefficient of additive genetic variance (CVA) - estimate of genetic variation in a population that is independent of environmental variation.
    Highly heritable traits can still be heavily influenced by the environment (Turkheimer et al.)
  60. 60Heritability and Natural SelectionHeritability is important to selection as heritability of a trait determines how easily selection can change it.
    Selection requires some amount of heritability to work or else there would be no way to pass on useful traits.
    High heritability = faster natural selection
  61. 61MalthusWrote a paper whose main principles inspired Darwin. Main claim made was that populations would grow exponentially if left unchecked.
    Exponential growth is prevented by finite resources limiting survival and reproduction.
    Competition for reproductive success occurs in each generation and phenotype can affect success. Even if survival for one trait is only marginally better, it will still increase in frequency over time.
  62. 62FitnessFitness: The number of copies that an allele will leave in the next generation and the change in allele frequency over generations.
    Calculated by the weighted average of relative reproductive successes of all phenotypes the allele affects, meaning sometimes alleles with a harmful effect can persist if it also has benefits.
    When trying to predict evolutionary outcomes, always calculate the relative fitness of alleles and not organisms/species.
  63. 63Natural Selection at a Phenotypic and Genotypic LevelEnvironmental conditions do not cause phenotypic mutations, but rather selects from the current variation in the population. Individual organisms cannot produce many phenotypic changes (apart from muscle growth, height, etc.) over their lifetime.
    Natural selection changes allele frequencies. The speed that an advantageous allele will increase in frequency is influenced by whether it is dominant (fast) or recessive (slow).
    Disadvantageous recessive traits take longer to eliminate as they only appear when homozygous..
  64. 64Natural Selection of Polygenic CharacteristicsWhen considering alleles contributing to polygenic traits (e.g. height), it is more complex as an allele that increases the trait may be present in those without it.
    On average, phenotypes with that allele have more advantage and so it will gradually increase in frequency, and so will the average level of the trait, over time.
  65. 65Group Selection and Wynne-EdwardsWynne-Edwards - some birds practice reproductive restraint (laying less eggs) when food is low. Believed that this reduces stress to prevent extinction and was therefore adaptive. Incorrect as members of the population who do practice RR (altruists) have less offspring (lower reproductive success) and so altruism will decrease over generations.
    Even in only-altruistic populations, a mutation may cause selfishness or a selfish bird may migrate into the colony.
    Therefore, behaviours promoting the collective advantage of the group at the expense of the individual are not likely to evolve.
  66. 66Evolutionarily Stable StrategiesBehaviour that, once common in populations, cannot be out-competed by alternative behaviours. E.g. infanticide in male lions puts the female back into oestrous, or height of trees (wastes energy but needed to gain sunlight). Could be described as an arms race as cooperation would be easier but is not possible as it would never reach fixation.
    Natural selection operates on immediate allelic advantage rather than long-term viability. Once an ESS is found selection keeps the population near to it.
  67. 67Kin Selection and Hamilton's RuleCollateral kin - siblings and cousins, sideways relations.
    Organisms will put themselves first apart from some exceptions, mainly parenthood. This is because children represent the future of the genome and parental protection is an investment in genotypic future. Also applies to collateral kin and is known as kin selection.
    Central component of this is coefficient of relatedness r. Hamilton's rule: behaviour that costs the individual but benefits relatives will only evolve if c < rb. E.g. foregoing 1 child so your brother (r = .5) can have 5 more children (c < rb = 1 < 2.5). Reproductive success should also include any reproduction done by siblings because of the individual's actions (inclusive fitness).
  68. 68Applications of Kin SelectionAlloparenting (helping individuals who are not offspring), e.g. bush babies will bring food to their younger siblings.
    Multi-cellular organisms - organ cells cannot reproduce so instead keep the organism alive so that it can pass on sperm/eggs (r between cells in the same body = 1).
    Kin-directed helping (helping kin by risking your own safety) shown in black-tailed prairie dogs. More likely to call and alert the pack to predators when there are kin present
  69. 69Constraints of Hamilton's RuleBehaviours will not evolve if c is too large in absolute terms (e.g. if makes all bearers sterile). Only works if the individual is only foregoing SOME offspring.
    r alone is insufficient to predict behaviour, e.g. offspring are less likely to protect parents than parents to protect offspring as b is lower (parents cannot reproduce again).
    r to collateral kin is always less than r to oneself and so kin selection can work against some kin (e.g. prairie dog mothers will kill nieces/nephews when they have their own offspring as r is greater).
  70. 70The Price EquationExpected evolutionary change for a trait depends on covariance with the fitness of the allele responsible (similar to correlation). Covariance is positive when increasing the level of the trait increases fitness. Positively covarying traits will increase over time.
  71. 71Suppression of Within-Group CompetitionThe only way for genes to replicate themselves is for the entire genome to be replicated (through reproduction). This allows the genome to function as a whole as all genes have the same interest.
    Meiosis works by making it a fair lottery so each chromosome has equal chance of being passed on, so all genes are still working together.
  72. 72Evolutionary TransitionsIn a number of points, separate free-living elements joined together to work as a collective: dna combined into genomes, which turned into eukaryotic cells, which became multi-cellular organisms. The next step is to become a eusocial multi-individual colony like bees and naked mole rats. Colonies could also be considered as only one individual.
    Eusociality is difficult to accomplish as most cooperation is disrupted by in-group competition.
  73. 73Intra-genomic ConflictThere can be some competition even in functional collectives (e.g. genes within an individual organism), often when one is slightly more fit than the other. Examples:
    • Transposable elements will replicate themselves without benefit to the collective organism (favouring their own interests).
    • Segregation distorters - alleles found in mice that distort meiosis to give them a better chance of going into gametes (90% chance). Work by disabling other sperms, even when the allele is bad for the carrier's health. Still low in frequency as the homozygote is lethal in males and causes bad health in females (low fitness).
    • Cytoplasmic male sterility in plants (mostly hermaphrodites) prevents ability to pollinate in the plant (the male behaviour), making the plant female so that it is able to also provide the cellular environment as well as a gamete.
  74. 74Modes of Selection• Stabilising selection: occurs in quantitative traits where selection leaves the average value the same as the average value is the optimum. An active force that creates no change.
    • Purifying selection: conserving an individual gene because mutations impair functioning (mutations being weeded out).
    • Directional selection: changes the average value because highest reproductive success is above the average.
    • Frequency-dependent selection: results in a mix of two variants as each only has an advantage when rare, e.g. Bluegill sunfish can be parentals (make nests) or cuckolders (infiltrate and fertilise nests). Cuckoldry cannot die out but is low in fitness when common.
  75. 75Mutation-Selection BalanceMutation introduces new variation into the population while selection aims to reduce it.
    Sustained selection can deplete variation and drive heritability to 0 (e.g. number of hearts in a human has strong selection and no variation).
    Mutation-selection balance - genetic diversity in a population depends on the relative strengths of selection and mutation.
    Frequency-dependent selection can help to maintain substantial variation.
  76. 76Maintaining Genetic Variation: Heterozygote AdvantageWhere fitness is higher for individuals with one copy of the allele than 0 or 2.
    E.g. heterzygotes of the sickle cell disease allele have some blood abnormalities that make them resistant to Malaria but not enough to cause illness. Homozygotes have deformed blood cells causing strokes, anaemia and lowered life expectancy.
    Selection will increase the allele in high-malaria environments until it becomes so common that there are many homozygotes, meaning that selection will reduce it.
  77. 77Maintaining Genetic Variation: Force of MutationVariation will persist if mutation is strengthened/selection is weakened.
    In polygenic traits, strength of mutation is directly proportional to number of genes involved as each gene has a chance of mutation.
  78. 78Maintaining Genetic Variation: Inconsistent SelectionVariation can persist if selection is inconsistent. If environment changes then the optimum will change, meaning that selection is weaker because it is changing directions often.
  79. 79Maintaining Genetic Variation: Sexually Antagonistic SelectionWhen traits have different optimums for males and females.
    Optimum height for men is taller than average (directional selection) and for women it is average height (stabilising selection).
    All genes apart from X and Y chromosomes spend equal amount of time in both males and females - fitness in both sexes affects selection.
  80. 80Selection and Adaptation: Nilsson & PelgerDirectional selection produces adaptation but it is not always as simple as a single-gene trait or mutation and sometimes many mutations are needed.
    Nilsson & Pelger used mathematical models observing 1% changes to the original eye layout and produced something very similar to the aquatic eye over 350,000 generations.
  81. 81Adaptationist Hypotheses and the Phenotypic Gambit• Adaptationist Hypotheses: If a feature is commonly found in an organism, it is probably an efficient design solution to previous issues. If not, then it would have been out-competed by something else.
    • Phenotypic Gambit - the process of forming AHs about phenotypic designs while being agnostic about the underlying genetic mechanisms. Useful but cannot be taken for granted due to many genes affecting multiple factors.
  82. 82Ultimate Explanation and Proximate MechanismUE - the explanation of how a design increased ancestral fitness.
    PM - an account of the genetic/developmental mechanisms causing formation of said characteristic.
    Natural selection favours the PM that produces the optimal phenotype with highest reliability and smallest cost.
  83. 83Constraints on Optimality: Time LagsEvolution has time lags (vestigial structures) and evolution does not always produce optimal design as structures cannot be erased instantaneously, e.g. Sickle Cell allele in African Americans is unnecessary as there is no Malaria in North America.
  84. 84Constraints on Optimality: Inconsistent SelectionIn an oscillating environment (e.g. yellow savannah some years, black others due to fires) can cause inconsistent selection. Usually resolved with phenotypic plasticity but this takes time to develop.
  85. 85Constraints on Optimality: PleiotropyChanges to one gene can affect multiple characteristics. Genetically correlated traits can hitch-hike (e.g. selective breeding for tame foxes ended with floppy-eared, curly-tailed, piebald foxes along with tameness).
    Genetically correlated traits can have opposing effects on fitness. Ornamentation (attractiveness) in male guppies associated with shorter lifespan. Organism will possibly never reach optimality unless selection can remove the correlation between traits (would take a long time).
  86. 86Constraints on Optimality: Shape of the Adaptive LandscapeSelection may not have been able to work in a way that cannot reach optimality. E.g. the human eye is sub-optimal due to the blindspot but any mutations removing the blindspot would not wire up neurally (leading to no eyesight and reduced fitness), so the eye is stuck beneath optimality.
  87. 87Testing Adaptationist Hypotheses and Function of MelaninAHs are easier to test than non-adaptive (e.g. genetic drift, adaptive landscapes) and if the AH doesn't work you can then think non-adaptively.
    Melanin absorbs UV light to protect tissues (UV radiation burns the skin, causes cancerous mutations and destroys folate (prevents NTDs like spina bifida)). Must be balanced to allow enough vitamin D synthesis to prevent rickets and osteoporosis.
  88. 88Testing Adaptationist Hypotheses: Reverse Engineering and Optimality ModellingReverse engineering examines possible purposes for a trait (e.g. melanin/skin pigment could balance UV light but could also act as camouflage). Accompanied by optimality modelling - looking at the expected design features for each purpose, e.g. women need more vitamin D due to pregnancy, so skin should have less melanin. Skin colour should be able to change with weather as well (Jablonski & Chaplin).
  89. 89Testing Adaptationist Hypotheses: ExperimentsExperimenters can manipulate a variable (Tinbergen et al.) or investigate natural variations to compare fitness.
    E.g. albinism (no melanin) is a rare mutation. Study of 1,000 Nigerian albinos found no one over age 20 without cancerous mutations or short life expectancy.
    White people with green/blue eyes and blonde/red hair also have a 60% increased risk of skin cancer.
    Children of white women have higher rates of NTDs and children of African Americans have more cases of rickets and osteoporosis.
  90. 90Testing Adaptationist Hypotheses: Comparative EvidenceComparing species or populations with differing conditions of selection, e.g. gannets live on cliffs and cannot be reached by predators so will not dispose of their eggshells from nests while other species do (Tinbergen et al.)
  91. 91Correcting Misunderstandings of Natural SelectionNatural selection is not 'for the good of the species', it benefits the individual. Group selection behaviours (improve the species at an individual cost) go extinct.
    Offspring can only be suited to an environment if they have the right genes (e.g. a black cat cannot have yellow offspring, even if the yellow fur is more adaptive).
    Mutation cannot be directed, it is totally random. Heredity also cannot be directed, it relies on allele frequency.
    Acquired characteristics cannot be passed on. Phenotype cannot affect genotype (the central dogma).
  92. 92Types of Reproductive SystemAsexual - making an identical copy of the self (common in single-celled organisms and fungi).
    Obligate/facultative sexual - organism is capable of both asexual and sexual. Sex is more common when cost is low/benefit is high (e.g. starfish).
    Isogamous - organisms are not male or female (have similar sized gametes). Gametes only fuse with gametes that have a different marker to their own.
    Anisogamous - there are males (small gamete) and females (large gamete) and they come in different forms:
    • Simultaneous hermaphrodites - have both male and female gametes/organs e.g. hamlet fish.
    • Sequential hermaphrodites - individual begins life as one sex and turns into the other later e.g. clownfish.
    • Dioecious - two sexes remain this way throughout the lifespan e.g. humans. Sex determination can be genetic or environmental.
  93. 93The Two-Fold Cost of SexCost of 50% of the genome when sexually reproducing compared to asexual. In isogamy, fertilisation is external and there is no gestation (equal cost) but there is risk of mutations or not finding other gametes.
    In anisogamy, female gestates the egg and sperm only provides DNA.
    Two-fold cost of sex is that females do all the work for only 50% of the genome. Endured because sex makes offspring more varied and it is more likely for at least one offspring to survive.
  94. 94Mutation and Efficacy of SelectionAsexual offspring are genetically identical except for when they mutate. Most mutations are deleterious and will be passed on to all offspring in asexual lineages, meaning the entire lineage has reduced fitness.
    Sexual species - only 50% of offspring have a mutation and so lineage is more likely to survive overall as some descendants do not have the mutation. Sex produces variation which increases efficacy of natural selection to remove the least fit.
  95. 95The Red Queen HypothesisIndividuals directly benefit from being different to their parents. Main reason for this is parasites, which can evolve faster in order to infect hosts more effectively.
    Novel combinations of genes/cells make it harder for parasites to win out as there is too much variation to cover. Parasites also reproduce sexually to try and get ahead of evolution.
    MHC (group of genes involved in immune defence) combinations that are unique are more advantageous, and animals tend to prefer partners with a different MHC.
  96. 96The Pluralist ApproachBoth Efficacy of Selection and the Red Queen Hypothesis operate within the role of sex. Asexual species have greater risk of extinction due to failure to evolve (EoS) and their offspring have higher mortality rates due to being more susceptible to parasites (RQH).
  97. 97The Evolution of AnisogamyCommon assumptions in models of evolving anisogamy include:
    • Initially two mating types with equal gamete size, but with some random, heritable variation in gamete size.
    • Larger gametes have some advantage (easily found, more resources, survive longer).
    • Producing larger gametes means the individual produces fewer due to higher energy cost.
    • Other mating type is selected to produce numerous small gametes for little energy.
    • Once specialisation is established it is difficult to reverse.
    Anisogamy is more common in multi-cellular organisms and isogamy in single-celled. Possibly because multi-cellular development requires more energy/resources and selection for larger gametes.
  98. 98Sexual DimorphismThe difference between 2 sexes of the same species, e.g.:
    • Mandrills are 2x larger than females and have bright facial colourings.
    • Male peacocks are brightly coloured and females are drab and have no train.
    This may be because of sexual selection: natural selection of ability to gain mates. If males with a feature get more mates then the feature increases over time, even if detrimental (e.g. makes it harder to avoid predators).
  99. 99Bateman's PrincipleMales reproductive success (given sperm production has little cost) is theoretically limited by the amount of females they mate with. For females, egg production has a cost and limit to number produced. No reproductive advantage to having more partners than necessary (especially true for animals with a gestational period).
    Bateman's Principle: male reproductive success increases with each partner to a greater extent than it does for females (Jones et al.). Also greater variance in reproductive success of males as females almost always find a mate whereas males must compete and be chosen (Clutton-Brock et al.).
    According to B's P, males should always take extra mates due to low cost and high benefit, whereas females should be choosier (high cost, low benefit). Pattern shown in grouses (males compete and are chosen, but accept all offers of mating).
  100. 100Intrasexual Competition and Sexual DimorphismMales tend to fight more than females, a form of intrasexual competition. Stems from Bateman's Principle - fighting is risky but benefit of victory is having more access to mates (more worthwhile for males).
    Consequences for the evolution of body size (advantageous in combat but takes more energy to grow). There is a trade-off where extra growth will not help and therefore they cease growing and start reproducing.
    Combat success is more important in males, so the trade-off point is reached later. Males invest more in body size (explains sexually dimorphic size in e.g. elephant seals). In species with no harems or fighting (e.g. harbour seals), males and females have more similar size.
  101. 101Female Choice and OrnamentationMales can also compete with attractiveness. Highly ornamented traits e.g. peacock trains are likely to have evolved as they make males more attractive. More ornamentation leads to more mates but there is also a trade-off where ornaments begin to impede survival (Møller).
  102. 102Ornamentation: The Sexy Sons HypothesisBegins with a slight female preference for a particular male trait (e.g. long tails).
    Females choose long-tailed mates, leading to birth of long-tailed (sexy) sons. Preference for long tails is also genetically correlated with the long-tailed gene so daughters prefer long tails.
    Selection subsequently favours both long tails and preference for long tails. As preference increases, fitness payoff for having a long tail and vice versa increases.
  103. 103Ornamentation: The Good Genes/Handicap HypothesisSince growing ornamentation has energy costs, those who develop the trait must be healthy (eating well, parasite resistant, healthy genes) to be able to spare enough energy to grow the ornament. Choosing the ornament means choosing a male with good quality genes.
    Ornamentation is invested in to signal quality to female, causing an over-exaggeration because of the implicated costs of a large ornament.
    Can work alongside the sexy sons hypothesis as the inherited preference for the ornament reflects a preference for good quality genes.
  104. 104Sex Role ReversalBateman's Principle states the sex which has the highest cost has least to gain from having more partners.
    Mammals: females lactate, gestate and care for the offspring, males have little cost.
    Species where parents share responsibility (e.g. penguins) there is less sexual dimorphism (costs are relatively equal).
    In species where males provide most of the care for offspring (e.g. pipefish, Jones et al.), females have less costs and more partners.
  105. 105Female Multiple Mating and Extra-Pair CopulationMost birds and some mammals form long-term pair bonds. Females often have multiple mates but only one social pair (extra-pair matings).
    When pair bonding takes place, the best males may already be taken, meaning the female will have to settle. Settling may occur in order to gain help with parenting and territory defence but it is better to be fertilised by the male with the best genes.
  106. 106Alternative Male Reproductive StrategiesBest way to get mates is to be the largest, most dominant, ornamented male, but not every male can have this. Leads to the development of secondary tactics.
    Great-tailed tackle - strong males defend territories and take social partners and extra-pair matings. Smaller mates cannot defend territories, so will either remain in the colony (picking up extra-pair matings and waiting for a territory to become free) or will roam different colonies picking up extra-pair copulations in each one.
    Alternative strategies lead to less reproductive success but it is still better than nothing.
  107. 107Bateman's Principle in HumansEstimates of the ratio of male:female reproductive variance show small ratio (similar variance) in contemporary Britain, slightly bigger in !Kung and Xavante (hunter-gatherers) and very high in the Kipsigis (farmers with multiple wives depending on wealth).
    Though variance is moderated by local social/economic factors, male variance in reproductive success is always higher in males, suggesting males have evolved to compete and females to be choosy.
  108. 108Big Males and Choosy Females in Humans and other PrimatesRate of sexual dimorphism varies with intensity of male-male combat. Gorillas defend harems and are twice the size of females. Gibbons are monogamous and have roughly equal-sized sexes.
    Humans are intermediate but closer to gibbons. Males are about 10% bigger than females and more likely to commit violent crimes and take risks (especially unmarried young men, prime reproductive age of 16-25). Females also tend to be choosier when selecting mates (Clark & Hatfield).
  109. 109Parental Investment in Humans: BussSlight paradox in research about choosiness as both sexes tend to be choosy when selecting long-term partners. This is because humans have long-term pairings and males make large investments in offspring.
    Buss - both sexes are choosy when looking for long-term partners and both value kindness and reliability. In 37 countries, females tended to place importance on material resources (investment and resources needed for childrearing) and men on youth and beauty (indicates fertility).
    Patterns explain human ornamentation as men aim to demonstrate their wealth/status whereas women try to emphasise cues of youth and health in their fashion.
  110. 110Strategic Pluralism in HumansConflicting data between male choosiness and male partner variety is to recognise alternative mating strategies in men and women.
    Mating can be costly for males but does not have to be if they have no post-copulation involvement, explaining desire for partner variety.
    Women may choose social partners that aren't the best genetic match but are prepared to invest. Surveys show a sizeable fraction of women have at least sometimes been unfaithful and a small fraction of children are not fathered by the mother's partner. Shows women seeking better genetic quality as more symmetrical (attractive) men report being a partner in extra-pair matings more often. Women in the fertile stage of the menstrual cycle also fantasise more about other men and are more likely to cheat.
  111. 111Definitions: Extrinsic and Intrinsic MortalityExtrinsic mortality: the risk of an individual dying due to environmental events (e.g. predators/lack of food).
    Intrinsic mortality: mortality due to the organisms own ageing or behaviour of the organism's parents.
  112. 112Post-Reproductive Periods and SenescenceHumans have a post-reproductive period not present in many species.
    Senescence - when function declines in physiology. Starts at 50/55 and gets much worse at 70.
  113. 113The Disposable Soma HypothesisGenes reside in a body that could die from external causes. The gene is potentially immortal (can be passed on) but the body disposable.
    Senescence is not advantageous to individuals but advantageous to the gene. Organisms reproduce to pass on genes in offspring, but both reproduction and self-repair require energy (there is a trade-off).
    The DSH - ageing is an accumulation of unrepaired damage to body cells. This is necessary in order to have energy to reproduce.
    Natural selection chooses a lifespan that maximises reproductive success. By the time the organism reaches senescence, selection is weakened due to the smaller age group size caused by extrinsic mortality.
  114. 114Evolution of Reproductive StrategiesSpecies with a high mortality rate will be selected to live fast and die young for ultimate reproductive success.
    Body size is associated with life history as growing large requires energy which delays sexual maturation and prolongs gestation and lactation. Even when body size is controlled for, mortality rate is still significantly associated with litter size, gestation rate etc.
    Individual differences in lifespan of similar sized mammals (e.g. bats and ground mammals) are likely due to differing vulnerability to predators etc.
  115. 115Human Reproductive StrategiesHumans have a long life history, large body size and sexual maturity occurs at 15yrs 9m. Usual litter size is 1. Estimates of a human baby's survival rate in a hunter-gatherer society is 0.6 (compared to 0.35 in chimpanzees). Due to this, humans have a maximum age roughly twice that of chimpanzees.
    Humans reproduce cooperatively (relatives help care for the child) which allows for faster reproduction.
  116. 116Human Reproductive Strategies: Pygmy Populations (Migliano et al.)Pygmy populations have adult heights below 155cm.
    Migliano et al. - pygmy populations such as the Aeta have shorter height and a faster lifespan as they live in high-disease environments, compared to the Turkana (non-pygmies) who live in the same area but have low mortality. It is more adaptive to stop growing and start reproducing earlier than non-pygmies.
    2 proximate mechanisms involved could be:
    1. Genetic differentiation in selection for timing of growth and puberty
    2. Phenotypic plasticity for the phenotype to alter development in response to the environment.
  117. 117Quality and Quantity of Offspring: Lack's Curve and Extra SiblingsFollowing a faster life history means that offspring will be smaller and receive less investment.
    Lack: if a bird had more offspring, its reproductive success would increase but the infant mortality would also increase due to need to divide and share resources. Trade-off suggests that ideal/expected clutch size is well below the maximum clutch size.
    Other researchers think the parent should also save energy for itself in order to survive until next breeding season (Daan et al.).
    Evidence suggests a trade-off in humans due to long period of dependency. Children with siblings have to share investments and resources (Helle; Nettle)
  118. 118Sex of Offspring: Trivers-Willard HypothesisThere are some mechanisms where women can encourage the offspring of a certain sex. Sex is genetically determined but women can promote differential success of X and Y sperm and differential implantation/survival of male and female embryos.
    T-W Hypothesis - a good quality female would be better off having a son as better-quality males have higher reproductive success, and quality in daughters does not affect reproductive success as much (Bateman's Principle).
    Has not been observed in all species and many studies have failed to find effect.
    Could suggest that women who have better nutritional condition or wealth are more likely to have sons (Gibson & Mace).
  119. 119Parental Care and InputMost organisms, there is no parental input post reproduction (e.g. only a minority of fish are cared for by one of their parents).
    Time and energy lost by parenting could have been used for food gathering or reproducing. Cost of caring must be outweighed by the benefits brought by offspring survival/condition. Benefits will eventually flatten off as care increases. Parents are selected to care until additional benefits do not exceed costs - b < c (facultative).
    Some parental care is universal in mammals (lactation) and birds (incubation & feeding) due to the necessity in order for offspring to survive (obligate).
  120. 120Forms of Parental CareCare can be uniparental or biparental. For biparental to occur then b must be outweighed by c given that there is ALREADY ANOTHER PARENT caring (explains why it is not often met).
    Uniparental is common in mothers in mammals and internally fertilising fish (gestation) and in fathers in externally fertilising fish (father fertilises after eggs are deposited).
    Biparental common in birds as eggs must be incubated and the mother must be fed frequently (large benefits to paternal involvement).
  121. 121Parental Care in Male MammalsMale mammals are facultative carers and often provide no care, females are obligate (gestation and lactation). Males also faced with a degree of paternity uncertainty.
    Benefits of offspring quality must still outweigh costs even when given that the MOTHER already cares for offspring and multiplied by degree of paternal uncertainty. Threshold is not often met and only 10% of mammal species have paternal care. Clearest exceptions to this come when social structure reduces likelihood of promiscuity.
  122. 122Infanticide in AnimalsMales that favour their offspring disfavour the offspring of other males. One of the most common causes of death in mammalian infants is killing by non-related males. Aims to bring mothers back into reproductive condition sooner so they can mate. Mating with a female reduces chances that the male will kill her offspring, therefore females in multi-male groups may mate with several males to discourage infanticide by giving more males the possibility of paternity.
  123. 123Paternal Investment and Uncertainty in HumansFemales tend to provide more care for children but paternal investment is widespread. Humans live in multi-male groups, so males may have evolved sensitivity to genetic relatedness to prevent allocating resources to others' children. Mothers of newborns are more likely to say baby looks like their father (especially in his presence) to reduce uncertainty and promote care.
  124. 124Selection for Paternal Investment in HumansMen would only be selected to care for offspring if there was some benefit but research shows benefit of a father is somewhat uncertain and may even be less than that of maternal grandmothers.
    Care may be so widespread because it is a form of mating effort/guarding - paternal investment increases the chance of reproducing again. Investment can also increase offspring quality (Nettle).
  125. 125Infanticide in HumansThe Ache of Paraguay - mother remarrying someone who is not the biological father doubles the child's risk of dying before 15.
    In Western society, stepfather presence also massively increases chance of child injury/death (Daly & Wilson).
    Children in households with stepfathers are also more stressed than those with biological fathers.
    Despite this, many stepfathers make great investments (likely a form of mating effort).
  126. 126Parent-Offspring ConflictBoth parents and offspring want offspring to do well but the offspring is more interested in this (100% related to the self and only 50% to mother and full siblings, the mother is 50% related to all offspring and so benefits of care are less for the mother). Any energy invested in a sibling is worth only half the benefit of investment in the individual.
    It is better for offspring fitness to be cared for for longer until b < ½c (as opposed to b < c in mothers).
    Evidence shows a battle between mothers and embryos during gestation - embryo will try to take even more resources. Conflicts also occur during weaning/the end of breastfeeding (offspring keep trying to suckle for longer).
  127. 127Selection for Grandparental CareIn most mammals, reproduction goes on until senescence, death closely follows cessation of reproduction. Grandparental care in humans in near-universal and grandmother presence can outweigh benefits of father presence.
    There is no grandparental care in most mammals. Menopause in humans may be selected to occur around age 50 as mortality in childbirth increases with maternal age and offspring are expensive to rear - grandmothers can better enhance reproductive success by caring for their grandchildren.
    No evidence that men are selected to grandfather and grandfather presence has much fewer positive effects. Male fertility does not cease as long before senescence as it does in females, so an adaptive value of grandfathering is not needed.
  128. 128Lineage Differences in Grandparental CareMatrilineal relatives have maternal certainty, but patrilineal relatives have at least some degree of uncertainty. Could expect a higher fitness return for matrilineal investment. Number of studies confirm that matrilineal relatives do indeed invest more.
    Greater cultural significance placed on the patriline (surnames, inheritance of land to sons) is likely related to Trivers-Willard as inherited wealth/status gives more benefit to sons' reproduction than daughters'.
    In situations where there is little to pass on or high paternal uncertainty, the matriline tends to become more important. Matrilineal societies tend to have higher paternal uncertainty and little transmissible wealth.
  129. 129Benefits of Group Living - Reducing PredationBeing in a group reduces risk from predators for 2 reasons:
    1. Dilution of predation - less chance of being killed by a predator in a large group due to there being more alternative targets (may be slightly offset by increased group visibility).
    2. Predators may be less effective at attacking groups as there is more chance of early detection. Individuals can also spend less time being personally vigilant.
  130. 130Benefits of Group Living - Joint ForagingPack hunters can take on larger prey. Joint ventures favoured when group return per individual is higher than solitary return. Also raises issues of cooperation as it is better to let others do the killing.
    When food was scarce, lions did better to hunt alone or in 5s/6s. Smaller groups had to hunt the same prey as solitary hunters but are less successful and have to share. Despite this the most common party size was 2/3/4, suggesting other factors controlling group size.
  131. 131Benefits of Group Living - Territory DefenceHaving a resource-rich environment is beneficial but also requires defence. Larger groups would be better at defence. Group defence would push non-social members of a species to sociality in order to compete for territory.
    Group size is limited by the size of resources in a territory - one can predict sociality in resource-rich patches of land.
  132. 132Benefits of Group Living - Care of OffspringWhen parental relationships extend over several reproductive episodes (including biparental care), a social group based around the monogamous couple and their current/recent offspring is formed.
    Lionesses in the same pride will pool their cubs together in creches from 6 weeks to 2 years. More females using the creche = more surviving cubs, involves protection from infanticidal males.
    Creches may also split task of breastfeeding (allomothering) while others gather food. Arises from joint usefulness as opposed to altruism.
  133. 133Benefits of Group Living - Information TransferSeeing the behaviour of others allows for social learning (e.g. in colony-living animals that forage separately and return to a base). Evidence shows that individuals can identify and follow successful foragers and learn other suitable behaviours.
  134. 134Costs of Group Living - Feeding CompetitionMany costs involved (e.g. risk of infection). Most documented is feeding competition - more mouths to feed means food runs out more quickly.
    2 responses to this: live together but forage separately, or retain group integrity and migrate quickly from patch to patch.
  135. 135Optimal Group SizeAs group size increases, benefits of group living level off but amount of food necessary still increases. An intermediate group size will reflect optimal compromise.
    Size is not always optimal because of population dynamics (members dying, member dispersion means they are solitary). Party only definitely splits up when all parties would gain.
    Evidence suggests a mechanism for detecting OGS - offspring may be more/less likely to remain in the natal group depending on original group size.
  136. 136Types of Mating SystemPromiscuity/asociality (multiple mates with no long-term bonds); monogamy (one mate); polygyny (one male, many females); polyandry (one female, many males).
    Monogamy, polygyny and polyandry can be short- or long-term (one or many breeding seasons).
  137. 137Determining Mating SystemCan be determined by ecology when care is uniparental or there is no parental care. Mammalian females distribute themselves for access to resources and male for access to females.
    If females disperse singly = monogamy.
    If females forage in groups = polygynous harems.
    If females are mobile but males would lose out by monopolising females = promiscuity. Females may benefit due to paternal uncertainty. Males will adapt to have larger testicles for larger ejaculates.
  138. 138Trends in Mating SystemsPolygyny is very common due to Bateman’s principle: more beneficial for males to expend energy recruiting multiple mates than it is for females to do so.
    Polyandry is rarer, more often associated with sex-role reversal.
    Monogamy much more common when care is biparental.
  139. 139Solitary Social SystemsCharacterised by a lack of mating pair bonds and a lack of same-sex relationships in adulthood.
    One sex can be solitary while the other forms groups for territory defence etc.
    Solitary species may aggregate temporarily to choose a mate.
  140. 140One Male, One Female Social SystemsStrongly associated with mating monogamy. Often the young delay dispersal and juveniles may help within the small family unit.
  141. 141One Male, Multiple Female Social SystemsOften the case for polygynous harems (associated with strong sexual dimorphism). Other males may be tolerated until they reach sexual maturity where they disperse to found/take over their own group (e.g. gorillas). Leads to many lone, wandering males with no group.
    Females tend to remain in their natal group (female philopatry) even though males disperse. Philopatry enhances benefits of group living as females tend to be related kin selection can lead to collective care.
    Prides of lionesses may be associated with small coalitions of males (most likely brothers) but too-large coalitions are disfavoured due to reduce reproductive success.
  142. 142Multiple Male, Multiple Female Social SystemsOften based on promiscuity but can also be monogamous or contain small harems.
    Though the social group is vast there is still likely to be dispersal of one sex and philopatry of the other. If there is female philopatry/male dispersal, the matriline becomes important. With male philopatry/female dispersal, the patriline is important.
  143. 143Consequences of Group Living - Dominance HierarchiesThere are likely to be conflicts over food and mate access. Dominance hierarchies may emerge to prevent constant lengthy confrontations. Hierarchies mean some individuals can constantly displace others from a resource.
    Rank can depend on size, age, strength, and support, and can be challenged by fighting. Ranks can be either dynamic or stable over time.
    Subordinates will accept low-rank positions in order to survive (cost of contest is higher than the benefit) but it is not adaptive.
    When hierarchies are stable, low-ranking individuals show the most stress and worse health. In unstable hierarchies, high-ranking individuals are more stressed.
  144. 144Consequences of Group Living - Cognitive DemandsThe social brain hypothesis - maintaining social relationships requires brain mechanisms and social animals therefore have bigger brains, especially in monogamy. Possibly due to a selective for greater cognitive capacities to manage a close, long-lasting relationship.
    There is a positive correlation (NOT causal) between primate brain size and social group size. Other factors such as longer life history and more access to resources in large groups may also increase brain growth.
  145. 145Human Groups - General TrendsHumans are social. Lack of social connections is found by most to be unpleasant and a risk factor for stress-related illness and depression.
    Social groups are typically large by primate standards. Multiple males and females with enduring mating bonds.
  146. 146Human Groups - Group SizeHuman neocortex is higher than any other primate. Dunbar predicted a maximum social group size (people we interact with) of 150. Found that hunter-gatherer societies (not constrained by laws/social hierarchy) have a mean social size of 150 and the Hutterites (rural, egalitarian Christians) have a maximum village size of 150.
  147. 147Human Groups - Dominance HierarchiesThere can be clear hierarchies (e.g. in the army) but these are more salient in large social structures where not everyone knows everyone else.
    In small groups there is a preference for egalitarianism and consensus.
    Evidence suggests being at the bottom of the hierarchy increases stress (Marmot et al.).
  148. 148Human Groups - Mating SystemsCross-cultural study in 1967 estimated 82% of human societies are polygynous (can be through serial monogamy as men are more likely to remarry), 17% are monogamous and 1% are polyandrous.
    Though most societies are polygynous, most marriages are monogamous.
    Could be concluded that humans are mildly polygynous.
    When men contribute more to their children, society becomes more monogamous. When there is more variance in male wealth, there is more polygyny (women prefer to be a rich man's second wife than a poor man's first).
  149. 149Human Groups - PhilopatryMost societies, neither sex disperses until marriage and then either the wife will move to the husband's family (virilocality) or the husband to the wife's family (uxorilocality).
    No consistent bias to either in hunter-gatherer societies, but virilocality is more common in subsistence farmers (shift of resources down the patriline).
    Contemporary societies are described as neolocal - couple establishes a new household away from the parents, due to more easily transmissible forms of wealth (money).
  150. 150Definitions and Classes of CooperationBehaviour that is selected to provide benefits to other individuals. 2 types:
    1. Altruism - behaviour affects the recipient positively but negatively affects the actor. Can only evolve through kin selection or some similar mechanism that directs the benefits to those carrying similar alleles.
    2. Mutual-benefit behaviours - positively affects both parties. Sometimes raises issues of cheating (putting in less effort for the same benefit) but mechanisms have evolved to discourage cheating as the behaviour can only be maintained by preventing cheating.
  151. 151Mutual-Benefit Behaviours - By-Product BenefitsNot all MBBs are due to cooperation and can be due to each individual following their own self-interest (e.g. dilution of predation). No cheating because benefit always occurs alongside cost.
  152. 152Mutual-Benefit Behaviours - Direct ReciprocityWhen A helps B, B will later help A. Can only evolve when benefit (b) outweighs the cost (c) and the individuals have a good chance of repeat interaction and reciprocation (w), c < bw. One must also be able to recognise who it is that helped them to prevent cheating. For example, 'live and let live' in WWI (cease fire to collect casualties) had low cost, high benefit, high chance of reciprocity and it was easy to spot cheaters.
  153. 153Mutual-Benefit Behaviours - Indirect ReciprocityHelping someone leads to a good reputation which can have personal benefits. Cheaters get a bad reputation and do not get to participate in future joint ventures.
    Indirect reciprocity can be an ESS when cost (c) is smaller than benefit (b) and there is high availability of accurate information about an individual's reputation (q), c < bq.
    Significant in humans as it shows how people can be generous when there is no direct returns to increase reputation (e.g. charity).
    People who feel visible are likely to increase cooperation (Bateson et al.).
    Human language gives high accuracy (q) as we can share info about someone's prior behaviour. Gossip is central to conversation in all culture and can deter cheaters (Sommerfeld et al.).
  154. 154Deterring Cheaters - PunishmentIf cheaters are punished then cheating is less encouraged because of the consequence.
    Presence of punishment sustains cooperation at much higher levels than when it is not present.
    Punishment can be seen as indirect reciprocity as people may punish others (even at their own cost when they were not personally wronged) to bring about reputational benefits.
  155. 155Definition of PlasticityAbility of phenotype to alter in response to experience.
    Nature or nurture cannot be determined but one can tell if a behaviour is robust (develops the same way in all countries) or plastic (form is altered by environmental input). Plasticity has selective advantage as learning provides solutions to adaptive problems e.g. tanning.
  156. 1564 Conditions for Plasticity to be Adaptively Favoured1. Population encounters a range of environmental variation over evolutionary history (through change over time or movement of the population).
    2. There are different optimal phenotypes in different environments.
    3. Mapping between environment and optimal phenotype is consistent (environment A always favours phenotype A).
    4. Reliable cues for the state of the environment in order to trigger phenotypic change. Must be some short-term regularity in the environment.
    Plasticity is useful when the environment changes over the long term but is regular over the short term.
  157. 157When Plasticity Won't Evolve - Costs of Plasticity• Mechanisms needed to produce plasticity are more complex than producing a fixed phenotype.
    • Complex mechanisms are more likely to go wrong.
    • Plastic mechanisms take longer to produce an appropriate phenotype as more stages are involved and it involves environmental cues.
    • Mechanisms can be triggered inappropriately by unreliable cues (e.g. a freak sunny day).
    • Can only expect plasticity to evolve when all conditions are met and also that b > c.
  158. 158Developmental Induction - Definition and Freshwater SnailsExposure to cues in early life induce a permanent phenotypic change.
    E.g. freshwater snails either grow elongated or rotund shells depending on whether they are born near crayfish or pumpkinseed fish. When born near pumpkinseed fish they also crawl out of the water as much as possible. Developmental induction is caused by reading chemical cues in the water.
    Chemical cues induce a permanent change, so it is only useful if early environment predicts later environment.
  159. 159Developmental Induction in HumansAdult phenotypes may be developmentally induced by prenatal resources. Low birth weight (babies light for their length) is a predictor of nutritional scarcity once born. Female babies with LBW reach puberty earlier and LBW babies tend to carry more fat in the middle of the body as adults. Individual is induced by predicted nutritional scarcity into having a fast life history and a metabolism that stores as many resources as possible.
    Early major stress can also induce an earlier menarche and faster life history strategy.
  160. 160Imprinting Definition and Filial ImprintingRelies on a key experience in a critical period (like developmental induction) to provide a template of some aspect of the world (e.g. salmon imprint on the chemical composition of the water in their natal location).
    Some birds have chicks that follow the mother (e.g. geese) and chicks must be able to identify the mother (mothers vary by appearance). Plastic method of filial imprinting allows chicks to imprint on whatever moving object that is nearby in the first 36 hours (only such subject is the mother in most cases but humans can also be imprinted on - Lorenz).
  161. 161Sexual ImprintingOne must identify what potential mates look like, but potential mates vary by appearance. One learns their mother’s/father’s appearance and in adulthood seeks another who looks similar. Usually works as a strategy for identifying a mate (Witte et al.; Bereczkei et al.).
    Sexual imprinting can last for life (Hansen et al.).
  162. 162Associative Learning - Classical ConditioningAdaptive as it allows us to explain regularities of the environment. Evolution cannot build associations so instead provides ability to learn associations in response to experience.
    Possible drawback is the chance of meaningless associations being formed due to coincidences. Best way to deal with this is that learning requires multiple associations and associations can be extinguished.
  163. 163Associative Learning - Instrumental ConditioningAllows individuals to do more of a behaviour that produces a reward in the current environment. Allows for trial-and-error learning about the best way to behave in an environment.
  164. 164Constraints on Associative LearningAnimals cannot learn all things equally well, e.g. taste aversions are more likely to occur and persist for novel foods than familiar ones.
    There is also preparedness, e.g. in fears (Cook & Mineka).
    Dynamics of learning (necessary pairings, timing, length until extinction) differ according to learning type, relationship between cues and outcomes and fitness payoffs of success and failure.
  165. 165Plasticity and Associative Learning in HumansAssociation contributes a lot to human ability to learn from experience.
    Adherence to moral norms like incest taboos may not be a result of conditioning but a form of developmental induction (Lieberman, Tooby & Cosmides).
  166. 166Social Learning Definition and ExamplesSocial animals can copy each others' behaviour. Useful for learning behaviours without risk of costly trial and error (e.g. rats only eat foods seen to be eaten by other rats, smelled on another rat's breath, and tasted in mother's milk - prevents poisoning).
    Mating behaviours can also be socially learned (Galef & White).
  167. 167Evolution of Social LearningOnly available to social animals or animals with at least some post-birth parental interactions.
    Benefits include removal of costly trial and error, but the potential cost is learned behaviours (from older individuals) may be outdated/sub-optimal due to environmental change/individual differences.
    Theoretical models predict social learning is most adaptive when:
    1. Individual learning is costly,
    2. Social learning is rarer (socially learned info will be 'fresher'/newer),
    3. Environment changes at an intermediate rate (slow - no point. Fast - information is outdated).
    Models show we cannot rely on social learning for everything.
  168. 168Cultural TraditionsSocial learning can lead to cultural traditions (e.g. local dialects in bird and whale songs - songs are socially learned).
    Fostering studies show traditions are socially learned and not genetically determined as individuals adopt traditions of the foster species.
    Can also be used to acquire traditions in getting food (e.g. macaques used to rub sand off of their sweet potatoes but learned socially to wash them until fixation).
  169. 169Human Traditions - Cumulative Cultural EvolutionHumans are dependent on social learning and therefore have many persisting traditions.
    Animal traditions tend not to gain complexity over time, while human traditions are added to and improved to yield better results until designs are so sophisticated they could not have been designed from scratch (cumulative cultural evolution). CCE occurs in humans due to their ability to teach, imagine and evaluate. CCE is a large part of how humans became so ecologically dominant.
  170. 170Similarities Between Associative Learning and Natural SelectionIn both systems there is variation in behaviour. If one variant improves performance, then it is increased in frequency and new variants arise from the improved baseline.
    Both will over time improve survival behaviours, they can produce the same behavioural outcomes. Saying something is adaptive can mean it was either socially or individually learned or evolved. Only difference is response speed to environmental change (fastest to slowest: individual, social, evolved).
  171. 171Costs of LearningLearning can produce maladaptive behaviours. Associative learning relies on association with reward but past behaviours may not be adaptive today (e.g. liking sweet foods).
    Costs of social learning is the risk of learning an obsolete behaviour (avoiding previously harmful foods that are fine now).
  172. 172How Learning Guides Evolution and Selection - The Baldwin EffectSome adaptive developments may require multiple independent mechanisms being formed (e.g. ability to signal presence of food and ability to recognise signals). Likelihood of mutations arising simultaneously to produce these is unlikely but each individual behaviour is useless on its own. If one behaviour arises by mutation, learning can provide the second behaviour (e.g. through association), giving it a selective advantage still. Baldwin Effect - the capacity to learn fills in a gap in a genetic system, then (if costs of learning are high) genetic mutations fill the gap and remove necessity for learning (genetic assimilation).
  173. 173The History of LifeCentral claim of evolution is that all living organisms are related to each other in a single phylogeny and there is always a common ancestor.
    History of life is continuous and therefore there is no real clear cut-off point between the human child and the non-human mother. It is difficult to say where a particular organism starts/stops, and it is better to ask when two species diverged or when certain characteristics occurred.
  174. 174The Concept of a SpeciesGenus (pl. genera) - a group of closely related species.
    Species is the first way to classify an organism. Species are identified by their biological name with a system created by Linnaeus. Species name consists of 2 parts, the genus (capitalised) and the species within. Sometimes a third term can identify a subspecies (e.g. Canis lupus signatus).
    Species are defined by reproductive isolation (no interbreeding with other species). Any interbreeding means they are only subspecies. Some discussion as reproductive isolation can be partial - due to physical separation of two interfertile populations, or interfertile species that choose not to breed with each other. Raises issues of cut-offs etc.
  175. 175Grey Areas in Species: The Genus CanisDogs and wolves. At least 6 species of wolf and dozens of subspecies.
    May be only one species of wolf as complete reproductive isolation is not demonstrated (e.g. fertile matings between dogs, wolves, coyotes and golden jackals). Difficult to know where to draw the line.
  176. 176Issues in Determining Species in TimeIt is difficult to draw boundaries between extinct species as we cannot use reproductive isolation as a criterion. Usual solution is to use different names for two organisms that are as phenotypically different as two living species would be (leaves some room for debate still). Beginning of a new species name therefore tends to be a matter of decision, not discovery.
  177. 177Higher Taxonomic UnitsNested, with each unit sitting inside a more inclusive grouping at the above level. Order is genus, family, order, superorder, class, phylum, kingdom, domain (e.g. Canis, Candiae, Carnivora, Laurasiatheria, Mammalia, Chordata, Animalia, Eukaryota).
    Taxonomies should reflect phylogeny and not resemblance due to common ancestors. Should also be monophyletic (contains the ancestor and all descendants). E.g. 'reptile' is not monophyletic as crocodiles are closer to birds than turtles. Determining where to define genus/family/etc. is mainly a matter of convention
  178. 178Establishing PhylogeniesCharacteristics used to classify organisms were originally morphological (skeletal or anatomical features). More often nowadays characters are molecular (sequences of genes, transposable elements, amino acids). Molecular characters that are shared by some but not all species under study.
    Characters must be retained from a common ancestor, as opposed to being due to convergent evolution - easier to ensure at a molecular level.
    Modern research can use computer programmes to search for the most parsimonious/likely one (parsimonious phylogenies are most likely to be true as it assumes the smallest amount of mutations) with included confidence statistics.
  179. 179Establishing Phylogeny in Whales - Nikaido et al.Studied 7 mammals and the presence of transposable elements at 20 loci.
    TEs were found at 4 loci in the whale and hippo but no others (whale and hippo are joined), and another 4 TEs in the cow and deer but no others.
    TEs found at loci for cows, deers, whales and hippos but not pigs, setting pigs apart from the rest.    Establishing Phylogeny in Whales - Nikaido et al.
  180. 180Establishing Phylogenies - The Molecular ClockMolecular changes/mutation is mostly neutral and probability of mutation remains about the same each generation. Therefore molecular differences in 2 lineages should occur at a constant, similar rate. More molecular differences = longer time since the lineages diverged. Can be used to estimate how long ago a branching event occurred.
    Issue that there is still variation in rate of change from molecule to molecule. Molecular clock must be calibrated for the lineages and molecules being studied (usually done by establishing evolutionary rate from fossil records).
  181. 181FossilsRemains of once-living organisms, usually preserved in rocks. Extremely rare due to the specific geological conditions needed and it is usually bones and teeth that are fossilised.
    Allow ancient creatures to be placed into phylogenies. Characters are usually morphological but more recently scientists have been able to extract DNA from bones (especially useful in human evolution).
    Fossils can be very accurately dated which allows for time brackets and calibrations of molecular clocks.
  182. 182Fossil Evidence in WhalesWhales are artiodactyls who all have a shared astragalus (a bone in the leg) - ancestral whales may have had this too.
    Fossils discovered from 50m years ago with legs and an astragalus (artiodactyls), and also features in the ear bones only found today in whales, showing them to be ancestral whales.
    Conclusion - whales descend from a legged ancestor and are artiodactyls.
  183. 183Fossil Evidence in FlatfishFossils can demonstrate how phenotypic characteristics developed by showing intermediate states.
    Flatfish lie horizontally in the water, as did their ancestors. Ancestral flatfish had one eye on each side of the head so the fish had to lift its head to see the sea bed. The further the eye migrated, the less head lifting was required and this created a greater selection pressure for greater asymmetry until one eye crossed over the midline.
  184. 184Features of PrimatesHumans are primates – group of mammals. Shared features separating them from other mammals:
    • One of five digits is opposed, can grasp with hands and feet (humans can’t use feet).
    • Relatively highly dependent on vision, not olfaction.
    • Forward facing eyes, binocular vision and some colour vision.
    • Relatively large brains for body size.
    • Ancestral habitat is usually arboreal.
  185. 185The Primate PhylogenyFirst branching is the strepsirrhines and haplorrhines. Strepsirrhines – mostly lemurs in Madagascar, can be large and diurnal (day dwelling) or small and nocturnal.
    First branching of haplorrhines is the tarsiers (single genus resembling lorises and sometimes classed with strepsirrhines as prosimians).
    Monkeys and apes form remainder, branching into platyrrhines (monkeys in the Americas) and catarrhines (Old-World monkeys/apes and humans).
  186. 186Lesser Apes – Gibbons13 species in 4 genera. Located in southeast Asia.
    Form long-term pair bonds and have territorial social groups (monogamous pairs plus dependent offspring).
    Specialised in hand, arm and shoulder for brachiation (swinging from branch to branch using arms).
  187. 187Great Apes – Orang-utansLive in Indonesia, 2 species/subspecies (Bornean and Sumatran).
    Primarily frugivorous (fruit-eating) and arboreal). The only apes to live in a solitary manner most of the time.
    Males defend a large range full of small female ranges – asocial polygyny with sexual dimorphism.
  188. 188Great Apes – Gorillas2 species – Gorilla beringei and Gorilla gorilla (endangered).
    Herbivores living on the ground. Form of locomotion is knuckle-walking.
    Highly sexually dimorphic and live in classic polygynous harems.
  189. 189Great Apes – Chimpanzees2 species – common chimpanzee and the bonobo (pygmy chimpanzee).
    Knuckle-walkers, but are smaller and more arboreal than gorillas. Common chimpanzees are omnivorous and occasionally hunt. Bonobos are more frugivorous.
    Live in multiple male, multiple female, promiscuous social/mating structures.
  190. 190The Ape PhylogenyHumans are great apes. Gibbons diverged from great apes first.
    Molecular phylogenies found humans are strikingly close to chimpanzees (99% resemblance in DNA sequence). Chimpanzees are equally close to humans as they are to orang-utans and gorillas.
    Contemporary ape phylogeny shows the human-chimpanzee divergence about 5-7m years ago (quite late).
  191. 191HomininsNo living animals closer to us than chimpanzees, but fossils show intermediate forms (collectively known as hominins).
    Not a single lineage and many branches are now extinct.
    Early hominins restricted to Africa – fossils in Chad/Kenya/Ethiopa date from near the human-chimp divergence. Generally chimpanzee-like in brain size/facial structure but show signs of bipedal locomotion.
  192. 192The AustralopithecinesDate around 1-4m years ago. Around the size of chimpanzees with unambiguous evidence of bipedal locomotion (in feet, pelvis, legs and spine) but short legs and arms (suggesting some time in trees). Canine teeth are reduced (continued in humans) suggesting omnivorous diet with a lot of fruit.
    Evolved when Africa was cooling/drying and forest depleting – provided advantage of bipedalism (more efficient and absorbs less heat due to depleted forest).
    Later diverged into the robust (stronger teeth and jaws with enlarged molars for chewing coarse plants) and gracile (ancestral to modern humans) forms.
  193. 193Origins of the Genus HomoFirst fossils to be given genus Homo were 2.5m years old, given names like Homo erectus.
    Genus is significant as this is where relative brain size moved away from chimpanzees and towards humans. Around time of emergence, stone tools appeared alongside animal bones (greater dependence on meat).
    Early Homo are the first hominins to migrate outside of Africa. Full bipedalism in place at this point making mobility higher.
  194. 194The Archaic Homo SapiensAppeared around 0.8m years ago. Larger overall with brains expanded so that body and brain size is within range of living humans. Associated with more complex stone tools than H. erectus.
    Often referred to as archaic H. sapiens but with some specific species names too like H. neanderthalensis – robust and cold-adapted, appearing in Europe 300k years ago and going extinct 30k years ago.
  195. 195Homo FloresiensisFossils from the last 20k years found on the Indonesian Island of Flores (well after arrival of modern humans). Thought to be a separate species - H. floresiensis.
    Much smaller than modern humans and H. erectus. Possess many erectus-like features like smaller brains, suggesting they may be a dwarf species of erectus (common on islands).
  196. 196Origins of Homo Sapiens/Anatomically Modern HumansFossils indistinguishable from modern humans found within last 200k years, oldest in Africa. Named as H. sapiens or anatomically modern humans (AMH).
    Dates show Neanderthals (Europe) and H. erectus (Asia) were around when AMH appeared in their area (likely to have been expanding during this time. Dates raise questions of whether species interbred or not and whether or not they are separate species or regional variants.
    Most popular model is the ‘out of Africa’ model (no interbreeding).
  197. 197Evidence for the Out of Africa Model – MorphologyIf there was continuity between H. erectus and contemporary Asians, or Neanderthals and contemporary Europeans, there would be shared morphological features.
    This has not been convincingly demonstrated but modern humans across the world tend to look like each other and resemble AMH fossils.
  198. 198Evidence for the Out of Africa Model – Genetics of Living HumansMolecular phylogenies constructed using human genome and human mtDNA (useful due to being passed on by mothers only and a high mutation rate making it good for even short time spans).
    Sequencing of the complete mitochondrial genome from 53 individuals over the world found that one can trace the phylogeny of humans (Africans, non-Africans, Europeans, Asians). Suggests all current humans can be traced to a small set of common ancestors.
  199. 199Evidence for the Out of Africa Model – Neanderthal DNAExtraction of Neanderthal mtDNA from bones showed that they were more like living humans than chimpanzees, but also outside the range of human variation. Evidence suggests that AMH replaced Neanderthals with little/no interbreeding.
  200. 200The History of Modern Humans – Colonisation and EpochsSmall population of AMH in Africa gave rise to colonisers, peopled all continents by 40k years ago. Around the same time stone tools became more complex/varied.
    Most colonisation took place in the Pleistocene epoch – characterised by quickly oscillating wet, warm interglacials and glacial periods of ice ages and arid tropics. Most recent glacial maximum was 19k years ago and after melting AMH entered the Americas.
    Current relatively warm period began 10k years ago and is called the Holocene – when agriculture, metalworking and towns appeared. 95% of AMH’s history was living as hunter-gatherers.

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Psychology (Stage 1) FlashCards sobre Evolution and Genetics Part 1, criado por Daniel Kirkbride em 25-04-2019.
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