Download Source: Holt Biology textbook, Section: Evidence of Evolution, Ch 13

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Source: Holt Biology textbook, Section: Evidence of Evolution, Ch 13, Sect 2, pg. 283 -­‐ 287 Objectives: • Describe how the fossil record supports evolution. • Summarize how biological molecules such as proteins and DNA are used as evidence of evolution. • Infer how comparing the anatomy and development of living species provides evidence of evolution. Evidence of Evolution The Fossil Record Fossils provide an actual record of Earth’s past life-­‐forms. Change over time (evolution) can be in the fossil record found in newer and older rocks. Fossils referred to as intermediaries are those that link current organisms with past (extinct), organisms. As a result, most scientists agree on the following points: 1. Earth is about 4.5 billion (4,500,000,000) years old. 2. Organisms have inhabited Earth for most of its history. 3. All organisms living today share common ancestry with earlier, simpler life-­‐forms. The fossils record is not complete, so it is believed that there are many animals that have never been known to those who study ancient organism. The conditions for fossil formation have to be just right for fossils to form. Animals with hard outer skeletons (exoskeletons) are more like to become fossils than soft-­‐ bodied animals. After the discovery of a fossil, paleontologists (scientists who study fossils) analyze the sediment around the fossil. Using a process call radiometric dating, they can get an estimate of the age of the fossil. Anatomy and Development When body structures of different types of organisms are compared to one another, we can sometimes see some similarities that may suggest some distant relationship. We call these type of structures homologous structures because when compared they look somewhat the same. Other organisms, like have parts of their anatomy (body structure) that either have no use or function, but may suggest a trait that was once there long ago. These structures are called vestigial structures. An example of this would be the tailbone of humans or the hind limbs of whales. Biological Molecules The nucleotide sequence in genes should change and build up over time as species evolve. So, scientists should be able to make predictions based on the fossil records of what they should expect to find as more fossils are found. With proteins, predicting was first done with the amino acid sequence found in several species. If evolution has taken place, scientists would expect to see less differences in amino acids sequences of species with recent common ancestors. One example of this is by compar-­‐ ing hemoglobin proteins in several species to find recent common ancestry. For example, Gorillas and humans have one amino acid difference in hemoglobin proteins, suggesting a recent ancestry. However, when comparing mice to humans, there is a difference of 27, sug-­‐ gesting a distant past ancestry. Not all proteins follow this pattern. Some protein sequences evolve more rapidly that others, so these predictions aren’t always reliable. The best predictions are made by basing them on large numbers of DNA sequences. SUMMARY: In the space below, write a paragraph summary of the notes. Be sure to incorpo rate as many of the lesson objectives as possible. Use a highlight to point out the most im-­‐ portant concepts of the notes, as they relate to the lesson objectives. Name / Date / Period
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