Evolution evidence

• Ancient Organism Remains: Darwin found many types of remains of ancient organisms. In addition to fossil layers, he saw other fossils, bones, insects in amber (hardened tree sap), and petrified wood. Another type of preserved organism, which Darwin did not find, is animals such as mammoths frozen and preserved in ice.

• Fossil Layers: Sedimentary rock forms in layers, with the oldest at the bottom and the youngest at the top. Fossils in the bottom layers are very different from the organisms alive today; Darwin didn't even recognize them. As one looks farther up, at younger and younger rock layers, the fossilized plants and animals become more and more familiar until they are a lot like organisms that are around now. The organisms also tend to become more and more complex. From this, Darwin concluded that organisms have not remained the same since earth's beginning, and that they have changed a lot, gradually becoming more and more complex. He also realized that as new species arise, other ones become extinct.
  
  
• Similarities Among Living Organisms: One type of evidence for evolution (evidence that organisms are related, descended from a few common ancestors, and change to adapt to their environments) is that organisms are similar to each other, but not exactly the same. Similar organisms have differences that help them adapt to their environments. Many organisms have similar body plans. Horses', donkeys', and zebras' bodies are set up in pretty much the same way, because they are descended from a common ancestor. As organisms adapt and evolve, not everything about them changes. The differences, such as the zebra's stripes, show that each species adapted to its own environment after branching off from the common ancestor.

• Similarities of Embryos: The study of one type of evidence of evolution is called embryology, the study of embryos. An embryo is an unborn (or unhatched) animal or human young in its earliest phases. Embryos of many different kinds of animals: mammals, birds, reptiles, fish, etc. look very similar and it is often difficult to tell them apart. Many traits of one type of animal appear in the embryo of another type of animal. For example, fish embryos and human embryos both have gill slits. In fish they develop into gills, but in humans they disappear before birth.This shows that the animals are similar and that they develop similarly, implying that they are related, have common ancestors and that they started out the same, gradually evolving different traits, but that the basic plan for a creature's beginning remains the same.