Transcript Part 1
UNIT 5 PART 1: EVIDENCE OF EVOLUTION Evolution is a gradual change over time. There are two kinds: Geological – a change in the earth over time Organic – a change in species over time “Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light, it becomes a pile of sundry facts, some of them interesting or curious, but making no meaningful picture as a whole.” --Theodosius Dobzhansky, "Nothing in Biology Makes Sense Except In The Light of Evolution," 1973 Evidence from the Past - Fossils A fossil is any trace or remains of an organism that has been preserved by a natural process. Scientists can compare these to living organisms to see if evolution has occurred. Special circumstances are needed for fossils to form and then usually only the hard parts are left. Relative Dating of Fossils Most fossils are in sedimentary rock which forms layers. If the layers are undisturbed the oldest is on the bottom and the youngest on top. Therefore, the oldest fossils are found in the bottom layer. This tells you which fossils are older. Determining the order of the fossils results in the fossil record. Absolute Dating of Fossils This will tell the actual age of the fossil. Radioactive Dating is the most accurate. Matching layers in the same region are the same age. This is called correlation. These are fossils that appeared around the same time all around the world. They can be used to match ages of rock layers in different parts of the world. Index Fossils Patterns of Evolution Earliest organisms were simple, later ones more complex. Unicellular organisms appeared before multicellular. Aquatic organisms appeared before land animals. There are sequences in the fossil record that indicate that later species developed from earlier ones through a series of gradual changes passed on from generation to generation. These occurred over millions of years in the species. The fossil record is considered the strongest evidence of evolution. Extinction Of all the species that ever lived less than one percent exist today. When the last of a species dies that species is said to be extinct. Extinction is forever. Quagga 1883 Golden Toad 1989 Tasmanian Tiger or Tasmanian Wolf 1936, 1986 Passenger Pigeon 1914 Evidence from Living Organisms The classification system that we use is based on similarities and differences in anatomy, embryological development, and biochemistry. Similarities indicate a common ancestor. The more similarities between organisms the more closely related they are. Anatomical Similarities Vestigial structures – parts that are reduced in size and have little or no function. Human appendix, tail bone, wisdom teeth and muscles that move the ears and nose Whale hip and leg bones Homologous Structures Parts that have similar structures and development (are built the same way) but have different functions: Human arm Cat leg Whale flipper Bat wing Indicates a common ancestor Analogous Structures Parts that have the same function but a different structure and development (they are made differently): Bird wing Insect wing Indicates evolution along different lines Embryological Similarities The embryos of closely related species show similar patterns of development. As development continues the embryo resembles the adult. The longer the embryos resemble each other, the closer related they are. Molecular Similarities The ability to read the amino acid sequence of proteins and the DNA of an organism letter by letter has enabled biologists to confirm evolutionary relationships. The more closely related organisms are, the greater the biochemical similarities will be in the sequences of DNA, proteins, and enzymes. The Origins of Life – Modern Hypothesis Biogenesis – living things come only from other living things. So where did the first living things come from? The most widely accepted view is the heterotroph hypothesis. Heterotroph Hypothesis Early conditions on Earth were different: Higher temperature Different atmospheric composition The oceans were a hot, thin soup where chemical reactions were likely to occur. An experiment by Miller showed that organic compounds could be formed under these conditions. cont’d. These organic compounds then formed structures that had some of the characteristics of life and began to grow and divide. They were called heterotrophs. Eventually organisms developed that could use light for energy and produce oxygen - autotrophs. This changed the makeup of the atmosphere which led to the development of organisms that could use oxygen for respiration. Because aerobic respiration is more efficient than anaerobic, organisms using aerobic respiration became dominant.