Darwin • Argued that living things have been evolving on Earth for millions of years
The Fossil Record • Darwin saw fossils as a record of history on Earth • By comparing fossils from older rock layers (lower layers) to fossils from younger layers (upper layers), scientists could document that fact that life on Earth has changed over time.
Geographic Distribution of Living Species • Many times, animals on different islands or continents were this way due to climate. • Remember however, that some continents had similar environments but different organisms
Homologous Body Structures • Scientists noticed anatomical similarities between existing organisms • Many have different functions but are constructed from similar bones • Each of these limbs has adapted in ways that enable organisms to survive in different environments • These similarities and differences help biologists group animals according to how recently they last shared a common ancestor
Homologous Structures • Structures that have different mature forms but develop from the same embryonic tissue • Ex: bones in the flipper of a whale and bones in the arms of humans
Analogous Structures • Serve the same function in different species but evolved independently. • Ex: wings of butterfly, bat, and bird
Vestigial Organs • An organ that serves no useful function in organisms. • Ex: appendix, tonsils
Similarities in Embryology • The embryos of many organisms are very similar (vertebrates)