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1.4 evolution

Patterns in evolution

  • Convergent evolution - when different organisms independently evolve similar traits
  • Anagenesis - gradual transformation (along branches) of one species into another (one species becomes another species)
  • Cladogenesis - rapid splitting of a species into 2 or more parts (one species splits into ≥2 species)

Processes of evolution

Sources of variation (what kind of progeny are produced?)

  1. Mutation
  2. Recombination
  3. Phenotypic plasticity
  4. Constraints

Modifiers of variation (what kinds of progeny are in the next generation?)

  1. Natural selection
  2. Sexual selection
  3. Genetic drift

Phylogeny

  • Diversification of lineages through evolution
  • Any scale: populations to massive groups
  • Temporal or just relative sequence
  • NOT about gross similarity
  • Emphasises shared novel traits, not primitive traits
  • Animal shares a trait with its neighbour
  • Further down you move the phylogeny tree, the more recent the animal is

How it’s reconstructed:

  • Anatomical, genetic, behavioural, fossil & other data
  • Computer algorithms find patterns (phylogeny) which represents the best estimate of evolutionary patterns (minimising assumptions involved, etc)

Adaptation

“A trait which enhances fitness & arose historically as a result of natural selection for its current biological role”

  • Requires:
    • Feature
    • More offspring production
    • Favoured by natural selection
    • Appeared in conjunction with its current function in its environment (was not previously used for another function)

Key innovations leading to adaptive radiations (both must coincide):

  • Key innovations - novel trait which originated in a particular lineage, providing evolutionary “advantages”, ex. Increased speciations, leading to adaptive radiation
  • Adaptive radiation - explosion of speciation in a lineage, that can be causally linked to its key innovation, involving ecological & phenotypic diversification

why study evolution?

  • Produced biodiversity
  • Harnessed by humans for breeding (artificial selection)
  • Crucial for host-parasite, drug-disease arms races
  • Phylogeny = good predictor of similarity; ex. Similar treatments probably work best on closely related species
  • Good vets should be broad scholars (know biology better, know patients better)
  • Every organism’s past history explains the way it is today & constraints its future
  • Many health problems arise when animals experience environments they did not evolve in (ex. Obesity in zoos)
  • Explains why vets are needed; no organism is truly optimised to even its natural environment