How do we know evolution has occurred (and still is occurring)?The Fossil Record
Fossils are some of the most important pieces of evidence for evolution. Looking at fossils from the past allows scientists to compare extinct organisms to the organisms still living today. Transitional fossils also help explain the path of the evolution of certain organisms. For example, fossils exist that are intermediates between land mammals and whales. These show how the whale evolved from an ancient land mammal and what the intermediate species looked like. Homologous/Analogous/Vestigial Structures Homologous structures are parts of an organisms body that are similar to other species in structure. These structures are evidence for a common ancestor because they show the relatedness of species through their anatomy and development. Analogous structures are different in that they show how organisms have evolved independently of one another. For example, insects, bats, and birds have all evolved wings for the purpose of flying, but the structures of these wings are very different. Another example of evidence for evolution is the presence of vestigial structures. Vestigial structures are parts of an organism that have no known function. It is hypothesized that these structures were functional in recent ancestors but have lost their function with the process of evolution. An example of a vestigial structure in humans would be the appendix. Comparative Embryology Many organisms show striking similarities in their early development. Examining the development of embryos of multiple organisms resulted in the discovery that embryological development is very similar in a wide variety of organisms. These similarities suggest that many organisms are very closely related. Molecular Homology You can better understand how related two organisms are by looking at their DNA. For example, human DNA is about 99% similar to that of chimpanzees. This fact shows that we are very closely related and most likely diverged from a common ancestor. Real Observed Examples Evolution has been observed in many cases. The easiest way to understand evolution is by thinking about bacteria strains that become resistant. One member of the population can develop a mutation that allows them to be resistant, and because this is a favorable trait, it will result in higher reproductive success. This will cause the population of bacteria to develop resistance over time. |
Information was gathered from these sources:
Biology: The Unity and Diversity of Life, 12th Edition
http://evolution.berkeley.edu/evosite/lines/IAtransitional.shtml
Biology: The Unity and Diversity of Life, 12th Edition
http://evolution.berkeley.edu/evosite/lines/IAtransitional.shtml