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Unformatted text preview: SEQ CHAPTER \h \r 1 Biology 1107 Lecture #40 Monday 04-19-10 Outline of todays lecture 1. Finish Evidences of Evolution (concept 22.3) 2. Human/Chimp relationship 3. Begin chapter 23 Evolution of Populations FINISHING UP EVIDENCES OF EVOLUTION Comparative anatomy Vestigial Structures .Some of the most interesting structures are vestigial organs , structures that have marginal, if any, importance to a current organism, but which had important functions in ancestors. For example, the skeletons of some snakes and of fossil whales retain vestiges of the pelvis and leg bones of walking ancestors. Recent discoveries include fossilized whales that link these aquatic mammals to their terrestrial ancestors. In addition to those cases in which we can observe evolution directly, we see evidence of evolution by natural selection in the much grander changes in biological diversity documented by the fossil record. homologous structures . Similarity in characteristics resulting from common ancestry is known as homology . Descent with modification is indeed evident in anatomical similarities between species grouped in the same taxonomic category. For example, the forelimbs of human, cats, whales, and bats share the same skeletal elements, but different functions because they diverged from the ancestral tetrapod forelimb. They are homologous structures . Comparative anatomy confirms that evolution is a remodeling process an alteration of existing structures. Comparative embryology. Sometimes, homologies that are not obvious in adult organisms become evident when we look at embryonic development. For example, all vertebrate embryos have structures called pharyngeal pouches in their throat at some stage in their development. These embryonic structures develop into very different, but still homologous, adult structures, such as the gills of fish or the Eustacean tubes that connect the middle ear with the throat in mammals. Molecular Biology The concept of homology also applies at the molecular level (molecular homology) and allows links between organisms that have no macroscopic anatomy in common (e.g., plants and animals). For example, all species of life have the same basic genetic machinery of RNA and DNA and the genetic code is essentially universal. Evidently, the language of the genetic code has been passed along through all the branches of the tree of life ever since the codes inception in an early life-form. Homologies mirror the taxonomic hierarchy of the tree of life. Some homologies, such as the genetic code, are shared by all life because they date to the deep ancestral past....
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