Natural selection

Natural selection

1. Evolution

   • The ceatetor, if he exist, has an inordinate fondness of beetles - Haldane - 3-30 million animal sepcec - 99% of all species are now extinct - species are not immutable 0 evidence can be seen in fossils and in action (e.g Galapagos finches)
     • why are there so many species and why do they seem so perfectly adapted to their environments? adaptation - function of a trait that has been evolved by natural selection - the scala naturae (the great chain of being) is wrong - humans are not at the top of a linear chain - evolution is a branch, not a chain - we are one primate among many
       • Darwin was not the first person to suggest that species evolved - his grandfather wrote. poem about evolution - Alfred Russel Wallace and Darwin came up with the first plausible mechanism - Thomas hugely. how extremely stupid of me not to have thought of it
         • Darwin drew a powerful analogy between artificial selection and natural selection - e.g the wolf to the dog - natural selection works in same way - struggle for existence, those who have certain trait will have better chance of surviving and thus will be naturally selected
           • "Multiply, vary, let the strongest live and the weakest die" Dawrin 1859

2. `Core principles

   • Variability, heritability, surplus offspring, nonrandom survival and reproduction
     • Variability - individuals differ - gives natural selection something to act on - variability within species can be so great that it can be hard to determine what distinguishes species - species can be hard to define -bio species concept = mating can produce viable offspring
       • Heritabiity - variability has to be transmitted from generation to generation (vertical transmission) - contrast this with Lamarkianism = the inheritance of acquired traits e.g if you dye your hair purple, your kids won't be born with purple hair - problem for Darwin if traits are heritable = blending inheritance - variability would be lost each generation - the main source of heritable variability comes from genes and genes done blend
         • Surpluss offspring - darwin and walliace were inspired by rev. Thomas Malthus who wrote essay on principle of population (the Irish were reproducing too quickly) - more offspring are produced than can be supported by the environment (carrying capacity) - things limit how fast things can grow - selection
           • Nonrandom survival - the blind watch maker - William pale - complexity could not arise by chance (e.g the eye) - the eye has actually evolved multiple times - survival and reproduction are not random - individuals with better suited traits are more likely to survive and produce offspring

3. Fitness

   • the 4 Fs - fighting, feeding, fleeing and reproduction - witness refers to the differential survival and reproduction of individuals - darwin never used the term fitness - fitness can be absolute and relative - humans don't have to outrun a bear - just have to outrun others
     • Adaptive landscape - the optimum solution can change - getting from one to the other would involve a reduction in fitness - organisms therefore do not always seem perfectly adapted to their environments
       • other sources of evolution - genetic drift - random - change due to chance - population bottlenecks and founder effects - small pop. go to new area

4. Genetics

   • Mendelian inheritance - Gregor Mendel - showed that genes are inherited without blending - work unknown to darwin - cross bred garden peas, focussing on simple variants - green/yellow seeds, smooth/wrinkled seeds
     • traits are controlled by discrete particles (now known as genes) - dominance - some particles can mark the expression of others - recessive - traits that are not expressed when paired with dominant
       • Phentoype = observable traits - genotype - genetic basis - law of segregation - Mendels first law - every individual has two copies for genes of a trait - pairs of these particles separate and get passed into different sex cells - they unite with another particle after fertilisation to form zygote - law of independent assortment - particles for different traits assort independently
         • some traits appear blended - some traits are polygenic - more than one gene codes for it - codominance and incomplete dominance - recessive traits can be hard to eliminate (hidden from natural selection) - this maintains variability

5. Molecular genetics

   • chromosome theory explained Mendel's laws - particles inherited from each parent jointly determine traits - particles are genes - genes are carried on chromosomes - gametes carry single copies of parental chromosomes - when gametes are formed, variants of genes equally likely to be transmitted
     • alleles are variants of genes - genes occupy unique positions on chromosomes (locus) - homozygotes have 2 copies of each allele, heterol only one
       • From genotype to phenotype - one gene, one effect - or polygenic, many genes, one effect - or pleiotropic, one gene, many effects
         • Crick, Watson and Franklin - helical structure - structural genes - code for proteins - gene - segment of DNA specifying the sequence of amino acids in protein - proteins function - structure, enzymes, hormones and regulatory proteins
           • Around 20000 genes in human genome - about 2% of the genome - noncoding elements can regulate gene expression - epigenetic - non genetic changes in gene expression - e.g montane voles are promiscuous but can become monogamous like prairie voles when non-coding gene sswapped

6. The modern synthesis

   • neo-Dawrinism (the modern synthesis) is the fusion of darwinian evolution by natural selection and mendelian inheritance - populations evolve, not individuals - natural selection is one force for changing allele frequencies in populations - others are - mutation, gene flow, genetic drift, non-random mating, meiotic drive
     • The selfish gene - selection ultimately acts on genes, not individuals - we are all gene machines - an organisms is just a genes way of making more genes

7. Population genetics

   • Evolution to a population geneticist - change in allele frequencies over time

8. Evolutionary histories

   • Analogies - convergent evolution - independent evolution produces analogous traits (e.g flying) - homologies - traits that look different but have same history - adaptive radiation - similarity by descent - produces homologous traits - com parties method - phlyoggenetic history and similar ecological pressures - vestigial traits. - have lost their function through evolution -