Biology Evolution (Natural selection, Proof of Evolution, Human evolution)

Evolution:

  • Bottleneck effect (Small population due to a sudden change in environment or mass hunting) - Exacterbates genetic drift - Genetic variation is reduced - Greater risk of extinction

  • Non-random mating - Inbreeding, Assortative mating (sexual bias toward individuals with certain phenotypes)

  • Inbreeding = less heterozygous genotypes, negative and positive effects

  • Assortative mating = 

  • Positive mating with other individuals with similar genotypes/phenotypes

  • Negative mating (dissociative) individuals avoid other individuals with similar traits (less than expected)

  • Mutations (such as insecticide resistance)- introduces new alleles/ genes into the gene pool

  • Gene flow - The transfer of alleles into or out of a population due to the movement of fertile individuals.

Speciation:

  • The evolution of a new species 

  • A species is a group of organisms that can mate naturally and produce fertile offspring. Different breeds of horse can interbreed.

  • Does not apply to asexually reproducing species.

  • New species can be produced through Geographical (allopatric separation) and Reproductive (sympatric separation) Isolation.


Allopatric Separation

  • The interbreeding population of one species (population then becomes divided due to migration, dispersion or when geography changes drastically through time or disaster)

  • Populations will then experience selection pressures differently & evolve separately. If environments are similar - the population may still evolve differently due to genetic drift.

  • Even if populations are re-introduced, they are now so different they cannot interbreed (are now reproductively isolated & are two diff species)


Sympatric Separation

  • Can be caused by physical, behavioural or genetic differences. (can take place in the same geographical area)

  • Evolved by polyploidy, founder effect and genetic drift

  • If meiosis fails, the gametes remain diploid.

  • If two diploid gametes produce a fertilised ovum, the resulting offspring will be tetraploid.

  • These offspring will then produce gametes with 4 chromosomes that cannot pair up with the gametes from the original species (2 chromosomes).

  • Various strawberry species evolved through polyploidy. Diploids, tetraploids, hexaploids and octaploids.

Evidence of Evolution:

  • Fossils provide evidence (older layers are more primitive)

  • Some fossils resemble modern animals (common ancestry)

  • Dating fossils: relative dating- estimates the time the organism lived. (Law of superposition, older layers = more primitive, newer layers = more modern)

  • Analogous structures (e.g. bird and bat wings) - are evidence of common evolutionary pressures producing similar solutions, i.e. convergent evolution.

  • Comparative anatomy (Vestigial structures: organs/functions early ancestor had)

E.g. Wisdom teeth, Whale/snake hind legs, Python femurs

  • Molecular and Genetic evidence (Biochemical Evidence) Two closely related species will have similar DNA, RNA and Protein (amino acid) sequences. Evidence of common ancestor’

Glossary:

Genetic drift is the change in frequency of an existing gene variant in the population due to random chance.


Founder effect is when a few individuals become isolated from a larger population and form a new one with a smaller gene pool (If an early founder had a recessive allele e.g. dwarfism, then many descendants would inherit this allele)


Polyploid is an individual/species whose chromosome number is a multiple instead of the usual doubling of the haploid number, e.g. triploid, tetraploid, or hexaploid. Common in plants.


Allopolypoid is a common type of polyploid where two different species interbreed and produce a hybrid (if it is sterile, it can propagate asexually)


Autopolyploid is an individual with more than two sets of chromosomes that came from a single species (non-disjunction in cell division)

Primate features:


  • Forward facing eyes

  • 5 fingers

  • Four upper and four lower incisor teeth

  • Nails on fingers and toes (not claws)

  • Large brains for body size

  • Flexible skeleton with arms that rotate in the shoulder socket


Common ancestor? - primates evolved from tree-dwelling, shrew-like insectivores 50 mil years ago. Group split into several divergent lines of evolution, creating modern-day primates.


Hominoids (Gorillas, Gibbons, Chimpanzees, Orangutans, Bonobos and Humans) - most recently evolved. We have the same common ancestor as these hominoids, with out last common ancestor with chimpanzees being 12 mya ago.


Common Ancestor theory: 

Dryopithecus - an ape-like mammal which appeared 25 million years ago. 

Ramapithecus - ape-like mammal, 14-16 million years ago (ancestor of the asian orangutan or apes and humans)

Australopithecus - Human-like ape found in South Africa 4-5 million years ago - bipedal & suited for tree climbing.

  • Their teeth tell us about their diet, many large molars = alot of fruit, seeds, insects & roots.


Homo Habilis (first example of the Homo genus)

Had a brain 50% larger than Australopithecus, probably scavenged meat from kills made by other animals.


Homo Erectus

Lived in caves, used fire, ate alot of meat, could have made rafts, may have communicated,

Cared for each other when ill.

Proof? Charcoal, Fossils found in caves, Disabled homo erectus found buried, 


Link between Homo Erectus and Homo Sapien?

  • Most recent species that is closely related to humans

Two theories: 

  • Homo erectus evolved seperately into homo sapiens, creating unique features in africa & asia.

  • Homo sapiens evolved in africa 200,000 years ago and began to spread out around the globe

Homo Neanderthals: (35,000-100,000 years ago)

Probably became extinct due to climate change or competition with homo sapiens

  • Diverged from h. heidelbergsis 300,000 years ago

  • Cave dwellers

  • Used tools (Blades, Spears) & Fire

  • Buried their dead

  • Communicated using sentences

  • Lived until age ~40