1. Evidence of Evolution

2. What proof do scientists have that evolution has occurred?
Scientists compare body structures, development before birth, and DNA sequences to determine the evolutionary relationships among organisms.

3. Evidence of Evolution
The evidence of evolution can be put into three categories:
1. Similarities in body structure
2. Similarities in early development
3. Similarities in DNA

4. Similarities in Body Structure
An organisms body structure is its basic body plan, such as how its bones are arranged.
Scientists believe that organisms that have similar structures inherited these structures from common ancestors and are therefore related.

5. Homologous Structures
Similar structures that related species have inherited from a common ancestor.

6. Vertebrates-animals with a backbone
Fishes, amphibians, reptiles, birds, and mammals all have similar body structures-an internal skeleton with a backbone.
Do all of these animals look the same?
NO! But they are similar on the inside, and because they all have a similar internal structure, they share a common ancestor.

7. Similarities in Early Development
An embryo is the stage of development before an organism is born.
The embryo of many organisms look very similar.
Scientists feel that this is evidence that certain organisms evolved from a common ancestor.

8. Similarities in Early Development
Before birth, these embryos go through similar stages.
For example, all three organisms have a tail and tiny gill slits in their throats.
These similarities suggest that these three vertebrate species are related and share a common ancestor.

9. Similarities in DNA
Scientists have compared the genes of different species to determine how closely related the species are.
Genes are made of DNA.
By comparing the sequences of the nitrogen bases of the DNA (A, T, C, G) of different species, scientists can infer how closely related the species are.
The more similar the sequences, the more closely related the species are.

10. Human DNA and Chimpanzee DNA are 98.77% Identical!!!

11. Combining the Evidence
Scientists have combined evidence from fossils, body structures, early development, and DNA to determine the evolutionary relationships among species.
Branching Tree-a diagram that shows how scientists think different groups of organisms are related. It also shows the order in which specific characteristics may have evolved.
The closer the organisms are on the branching tree diagram, the more closely related they are.

12. Which animal does not have a bony skeleton?
What do rodents, rabbits and primates have in common that the other organisms do not?
Crocodiles are most closely related to which organisms? Why?