Types and Models of Evolution

1. Types and Models of Evolution Biology 11

2. Speciation The process of how new species evolve from old ones Two individuals are of the same species if they are able to interbreed and produce fertile offspring

3. Process of Speciation • Often due to reproductive isolation • when two populations are separated so they can no longer reproduce • Reproductive isolation can occur due to geographic barriers such as rivers, mountains, roads…

4. Once populations are separated, natural selection increases the differences between them As populations become better adapted to different environments, gene pools become more dissimilar Over a long period of time gene pools become so different they are separate species

5. Types of Evolution Divergent evolution Process in which one species gives rise to many species Also known as adaptive radiation: a number of different species diverge from a common ancestor Usually have homologous structures

6. Homologous structures

7. Example of divergent evolution and adaptive radiation: Darwin Finch Start with one type of beak and the species evolves many different beak types to fit each niche

8. Convergent Evolution Structures from different species become similar (analogous) in order to deal with similar situations Analogous structures have different origins and internal structures but similar purposes

9. Example: Bat wing and Butterfly wing

10. What similar structures do you notice?

11. Sisters separated by 135 million years

12. Speciation Rates • How fast does this happen? Theory 1: Gradualism • Gradual adaptations over time • Fossil records support this for some species (million year scale)

13. Theory 2: Punctuated Equilibrium Model • Long periods of stability punctuated by burst of change (10 000) years or less to evolve • Some fossil evidence supports this as well