EVOLUTION - L3,P2

EVOLUTION - L3,P2

1. how we behave today and how our brain performs is due to what our ancestors have had to go through

   • until 200 years ago, it was believed that species were created separately
   • naturalists (students of animal life and structure) doubted this
   • fossils of extinct species provided evidence for evolution - gradual change of species
     • FOSSILS
       • record to date how old they are
       • DNA analysis can quantify the differences between species and also estimate their divergence from a common ancestry, through the rate of DNA change

2. HOMOLOGY

   • similarity based on common ancestry as with forelimbs - human arm, dog foreleg, seal flipper, bat wing
   • different on surface but the structure and ways bone are put together, there is a similarity
   • DARWIN AND WALLANCE
     • produced evolution by natural selection - evolution proceeds by differential success in reproduction
     • DARWIN AND FINCHES
       • In every island there was a sub species of the finch - modification due to food needed - beaks changed to feed more efficiently
         • reproduction will increase a population, individuals of species are not identical, some variation is inherited, not all offspring survive to reproduce
           • inferred that variations affect the probability that they will survive to reproduce - adaptions increase the likelihood of offspring
       • SEXUAL SELECTION - each sex has anatomical and behavioural features that flavour reproductive success
         • CONVERGENT EVOLUTION
           • Similarities in behaviour or structure among unrelated animals due to adaptations to similar environments
           • seal, tuna fish have evolved fins - learned to adapt to their environment in a similar way despite being completely different species
           • HOMOPLASY is the resemblance between features such as body shape due to convergent evolution

3. HOW DO THESE VARIATIONS OCCUR?

   • DARWIN - evolution is a continuing process
   • HUGO de VRIES - mutation theory
   • the genotype or genome is all the genetic information of an individual
     • the phenotype is all of the physical characteristics that make up the being from the genome (of an individual at one particular time)
       • can account for evolution of even complex structures (over enough generations)
   • a mutation are spontaneous changes in genes, a rapid form of evolution. Spontaneous and random mutations in plants and animals results from changes in genes
     • unfavourable - selected against/beneficial - inherited

4. HOW DO YOU CLASSIFY

   • In Linnaeus's system of classification each species has two names:
     • Genus: a group of species that resemble each other
     • Species: a group of individuals that can interbreed and produce fertile offspring
     • example: homo sapien

5. FAMILY TREES

   • phylogeny - evolutionary history of a particular group of organisms and may be represented as a family tree
   • different species show different solutions to environmental changes (city rats vs country rats)
   • living animals, along with fossils, allow study of the body and brain

6. EVOLUTION OF THE NS

   • structures range from nerve nets, radial nerves, neural rings and simple ganglia in invertebrates to CNS and PNS in vertebrates
   • All vertebrate brains share the same basic structures ------ Relative sizes, proportions, and anatomical locations of these brian structures have been subject to evolutionary modification as the species have adapte to their unique ecological niches

7. HUMAN VS RAT BRAIN

   • each of the main structures in the human brain has a counterpart in the rat brain
     • differences: size, weight, amount of cortex, size of olfactory bulb (smell)
     • similarities: development from a hollow dorsal neural tube, bilateral symmetry, regional segmentation, hierarchical control, separate PNS and CNS, localisation of function (memory, visual, attention)
     • all vertebrate brains share the same basic structures
       • have all of these features in common because they descended from a common ancestor that possessed them
       • in general, vertebrate species with larger bodies tend to possess larger brains, larger neurons and dendritic trees

8. HOMINID EVOLUTION

   • hominid brains enlarged rapidly in our recent evolution
     • the use of tools reduced the necessity for large jaws and teeth, so they become smaller
       • as homo erectus evolved, brains became larger and faces got smaller
       • they also expanded their area over three continents
       • with homo sapiens, brain volume evolved rapidly and had reached modern levels about 150,000 years ago

9. many factors led to rapid evolution of a large cortex in primates

   • costs and benefits of large brain
     • prolonged dependence on parents, high metabolic cost, complex genes vulnerable to mutation
   • adaptive advantages:
     • increased survival and ability for group interaction in humans
     • innovative behaviour, use of tools and social learning in all primates