BIOLOGY 11

Types and Models of Evolution

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

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…

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

Types of Evolution

Divergent evolutionProcess 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

Homologous structures

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

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

Example: Bat wing and Butterfly wing

What similar structures do you notice?

Sisters separated by 135 million years

Speciation Rates

How fast does this happen?Theory 1: Gradualism

Gradual adaptations over time Fossil records support this for some species (million

year scale)

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