The Theory of Evolution What exactly is a theory? A theory is a well tested concept that explains a wide variety of observations. A theory should be able to make predictions about future observations. What is Biological Evolution? Biological evolution is the change that species undergo over time. More precisely, it is the change in the gene pools of living populations of species which occurs over time. What exactly does theory of evolution state? All life forms (species) have developed from other species. All living things are related to one another to varying degrees through common decent (shared common ancestors). All life on Earth has a common origin. In other words, that in the distant past, there once existed an original life form that gave rise to all subsequent life forms. The process by which one species evolves into another involves heritable genetic mutations. How does Natural selection Work? Any Species of animals produces more offspring then the environment can handle. There are individual differences among the offspring (mutations). Because too many offspring are in the environment only some will survive. Those that possess traits to survive best in the environment will survive. Those that do not die pass on their genetic code to their offspring. In this way only the fittest of the species will survive and through this process of Natural Selection evolution or changes occur in the species. What is the Evidence for Evolution? Fossil Record Biogeography Comparative Anatomy Comparative Embryology Comparative Biochemistry Fossil Record Organisms have changed over time. Some present species are not present in the fossil record Some current species are similar, but not identical, to some previous species. Biogeography Organisms evolve to adapt to their particular environment, then spread to other locales. Evidence comes from the distribution of similar species found around the world Biogeography Comparative Anatomy Related organisms share a unity of body plan. The same body structures can perform adaptive functions. Among vertebrates, forelimbs have the same set of bones. Homologous Structures Comparative Embryology Related organisms develop similarly. Early embryos of all vertebrates are very similar Early development reflects evolutionary origins - “Ontogeny recapitulates phylogeny” Do these look Similar? Comparative Biochemistry All living things use the same basic biological molecules for similar functions. - The nitrogen bases in all organism are the same: A T G C. Metabolic systems are similar among species. - Photosynthesis, respiration, fermentation, etc. Basic cell structure is almost universal. Vestigial Organs Hunan appendix is useless yet in other mammals, including primates, it is necessary to aid in digestion of high cellulose diet. Human external ear muscles still present but useless. Humans have tailbones and some babies are occasionally born with tails. Some snakes have skeletal limbs. Misconceptions about Evolution Evolution only progresses forward Reality: There are several species including the crocodile and the shark that have remained virtually unchanged for millions of years Man evolved from monkeys Reality is that man is on different branch of the evolutionary tree than monkeys. Evolution occurs in individuals Reality is that evolution occurs in populations. There are no modern intermediate species Consider the platypus! It is a mammal that lays eggs. Different Model of Evolution Evolution always occurs very slowly Reality: Punctuated evolution can occur over a relatively short time.