Evidence of Evolution

The Fossil Record Darwin saw fossils as a record of the history of life on Earth Darwin proposed that the Earth was many millions of years old Countless species had come into being, lived for a time and then vanished By comparing fossils from older layers with fossils from younger layers you could document that life on Earth has changed over time

Geographic Distribution of Species Similar but unrelated species puzzled Darwin Similar animals in different locations were the product of different lines of evolutionary descent

Homologous Body Structures Anatomical similarities among the body parts of animals with backbones Example: limbs of reptiles, birds, and mammals Vary greatly in form and function Constructed from the same basic bones.

Homologous Body Structures Homologous structures— structures that have different mature forms but develop from the same embryonic tissues These similarities and differences help biologists group animals according to how recently they last shared a common ancestor

Vestigial Organs Not all structures serve important functions Organs of many animals are so reducing size that they are just vestiges, or traces, of homologous organs in other species Why would this happen? One possibility is that the presence of a vestigial organ does not affect an organism’s ability to survive

Embryology Early stages, embryos, of many animals with backbones are very similar Demonstrates that the same groups of embryonic cells develop in the same order of all vertebrates. Common cells and tissues, growing in similar ways, produce homologous structures.