Evidence of EvolutionSec 8.2

Biogeography The study of the past and present

geographical distribution of species populations

Many of Darwin’s observations were based on biogeography

Example 1 Geographically close environments are

more likely to be populated by related species than are locations that are geographically separate but environmentally similar.

Desert and forest in South Africa vs. desert in Africa and forest in Australia.

Ie. Cacti are found in North, Central and South America deserts, but not in any other deserts.

Example 2 Animals found on islands often closely

resemble animals found on the closest continent.

Suggests island animals have evolved from mainland migrants with populations adapting over time to their new home.

Ie. Lizards in Canary islands (NW African coast) are similar to those in West Africa

Example 3 Fossils of the same species can be found

on the coastline of neighboring continents.

Continent location is not fixed and continents are slowly moving away from one another.

Africa and south America were once joined.

Example 4 Closely related species are almost never

found in exactly the same location or habitat.

Evidence from Anatomy

Homologous structures Structures that have similar structural

elements and origin but have a different function.

Similar because they were inherited from a common ancestor.

Differ in anatomy based on an organism’s lifestyle and environment.

Can be similar in structure r function or both.

The lower limbs of the human, frog, and horse all perform movement on land.

Hair in mammals is homologous – similar structures but may have different functions.

Analogous structures Structures of organisms that do not

have a common evolutionary origin but perform similar functions.

The wings of insects, birds, bats and pterosaurs (extinct flying reptiles) are similar in function but not structure, which means they do not share a common ancestor with wings.