1. Evidence of Evolution
Many of you asked what evidence there is for evolution. The short answer is that there is a lot of evidence that supports the theory of evolution. That’s why it is called a theory and not a hypothesis. There is evidence of evolution in homologous structures, embryology, DNA evidence, and fossils. We will examine each of these in more detail today.

2. Review: Natural Selection is the Mechanism of Evolution
Natural selection is what makes evolution happen! Organisms that are more fit are more likely to survive and pass on their genes to their offspring.

3. The Fossil Record
Fossils are the remains of ancient life. Different layers of rock have formed at different times during the Earth’s history. By comparing fossils from older rock layers with fossils from younger layers, scientists documented the fact that life on earth has changed over time.

4. Geographic Distribution of Living Species
The distribution of living things on earth provides information about the past histories of both living things and the surface of the Earth. This evidence is consistent not just with the evolution of life, but also with the movement of continental plates around the world-otherwise known as plate tectonics. Marsupial mammals are found in the Americas as well as Australia and New Guinea, shown in brown on the map at right. They are not found swimming across the Pacific Ocean, nor have they been discovered in Asia. There appear to be no routes of migration between the two populations. How could marsupials have gotten from their place of origin to locations half a world away? Fossils of marsupials have been found in the Antarctic as well as in South America and Australia. During the past few decades scientists have demonstrated that what is now called South America was part of a large land mass called Gondwana, which included Australia and Antarctica. Marsupials didn’t need a migration route from one part of the world to another; they rode the continents to their present positions.

5. Homologous Structures
Homologous structures have different mature forms, but develop from the same cell types in embryos. The limbs of birds, mammals, and reptiles have very different shapes and functions, yet, they are all made up of the same basic bones.

6. Comparative Embryology
The early stages, or embryos, of many vertebrates are very similar. This does not mean that a human embryo is ever identical to a chicken or fish embryo. What do these similarities mean? It is clear that the same groups of cells in embryos develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. These common cells and tissues, growing in similar ways, produce homologous structures.

7. DNA and Protein Sequence Evidence
All cells use on DNA to make protein, suggesting that this has been passed down from an ancient common ancestor. Biologists can study the amino acid sequences in proteins to determine evolutionary relationships among various species. Biologists have found that the more closely related two species are, the more similar the amino acid sequences of their proteins. Such comparisons allow scientists to show evolutionary relationships between different organisms. Since DNA molecules are highly conserved and passed from one generation to the next, base sequence pattern indicates evolutionary relationships. Matches in base sequence between species show how closely related the species are. For example, in the picture you can see that more matches are made between a human and a chimp’s DNA than between a human and a chicken. This indicates that the human and the chimp shared a more recent common ancestor than the human and the chicken, and are closely related.