Evolution Part 2 Pathways of evolution Speciation Convergent

Evolution Part 2 Pathways of evolution

• • • Speciation Convergent Divergent Gradual change Punctuated equilibrium

Speciation • The origin of a new species in evolution • A species occupies a unique niche (food, shelter, behaviour) in the environment carnivorous Eupithecia (inchworm)

Speciation • Competition for the same niche results in the extinction of the less efficient (fit) species, unless this struggle prompts one group to find a new niche (migrate)

Divergent Evolution • The formation of a new species from common ancestor • Occurs when: – A group becomes reproductively isolated by a physical or behavioral barrier from the rest and 2 gene pools are formed. – Gene pool becomes progressively more different since environments are different so selection pressures are different – Reproductive isolation further enforced and a new species is formed.

Divergent Evolution • Evidence for divergent evolution includes: Ø homologous structuressimilar structures derived from a common ancestor Ø embryonic developmentyoung embryos of various vertebrates look the same

Convergent Evolution • The acquisition of the same biological trait in unrelated lineages • Can be observed if different species evolve similar appearance due to living in similar environments. • Seen as analogous (different species, same function) structures – Eg. Wings of insects, birds and bats

Speed of Evolution Agents: 1. Gradualism – slow and steady change over time as proposed by Darwin

Speed of Evolution Agents: 2. Punctuated Equilibrium: long stable periods interrupted by brief, rapid periods of change. Occurs when niches are opened through: Ø mass extinction Øisolation of small populations Ømigration to new environments. Called adaptive radiation eg. Finches of the Galapagos islands.