A study of the position and shape of the bones in the forelimbs of a flying squirrel, a bat, and a beaver showed that the beaver and the flying squirrel appear to be most closely related. The diagram below shows undisturbed sedimentary strata at the bottom of an ocean. Two nucleotide sequences found in two different species are almost exactly the same. The diagrams below represent stages in the embryonic development of four organisns. Evolution is a predictable change from simple to complex organisms.
Evolution is a process of change through time.
Evolution often proceeds from complex to simpler organisms. Evolution causes organisms to develop characteristics they need. In Yellowstone National Part, some species of algae and bacteria can survive and reproduce in hot springs at temperatures near the boiling point of water. The diagrams below show embryos of three different vertebrate species. According to one theory, similarities in these embryos suggest common ancestry.