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: homologous structures- similar structures derived from a common ancestor embryonic development- young 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: 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: mass extinction isolation of small populations migration to new environments. Called adaptive radiation eg. Finches of the Galapagos islands.