6.2 Notes Evidence of Evolution

Interpreting the Evidence Fossils Patterns of early development Similar body structures

Fossils By examining fossils, scientists can infer the structures of ancient organisms. Fossils show that, in many cases, organisms that lived in the past were very different than organisms alive today.

Similarities in Early Development Scientists also comparing the development of different organisms. If you look at a fish, salamander, chicken and opossum, how much do they look like each other?

Now look at then during early development. All four organisms have a tail and a tiny row of gills.

Similarities in Body Structure Fishes, amphibians, reptiles, birds and mammals all have similar body parts. Examples: Back bone Internal skeleton

If you look closely at the structures of their limbs, you can see that they have similar bone structures. We call these similar bones homologous structures.

Inferring Species Relationships Scientists have combined the evidence from DNA, protein structure, fossils, early development, and body structures to determine the evolutionary relationships among species.

Similarities of DNA Why do so many organisms resemble each other? They all have DNA which is made of the same pieces: T, A, C, and G.

Branching Trees Scientists use the combined evidence to create branching trees. A branching tree is a diagram (picture) that helps show how scientists think different groups of organisms are related.

How do New Species form? A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits. Group members can be separated by things like: River Volcanoes Mountain ranges Being on islands

Squirrelly new Species Abert’s squirrel and the Kaibab squirrel both live in forests in the Southwest. These populations are separated by the Grand Canyon.

They both belong to the same species, but have slightly different characteristics. It is possible that someday, these squirrels may become so different from each other that they may become separate species.