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Evidence for Evolution Macroevolution Large scale changes that take place over a long period of time that create and eliminate species. Microevolution Short time scale events (generation-togeneration) that change the genotypes and Evidence for Macroevolution Fossils Record Comparative Biochemistry & Molecular Biology Comparative Morphology Vestigial Structures Comparative Embryology Evidence for Evolution – The Fossil Record Fossil Record Fossils are the remains of ancient life. When fossils are arranged according to their age, a progressive series of changes are seen. The Law of Superposition states that a layer of rock is older than the layer above it. Radioactive Dating can be used to date rocks layers rocks in which fossils occur, we can get a very accurate idea of how old the fossils are. This allows fossils to be arranged by their relative age to each other. This allows for a time frame for when fossils formed. Transitional forms are evidence for evolutionary change. Fossil Gaps Gaps remain in the in the fossil records of many species, although a lot of them shrink each year as new fossils are discovered. These gaps do not indicate weakness in the theory of evolution; they point out uncertainties in our understanding of exactly how some species evolved. Dinosaur tracks are common occurrences in the southern and eastern U.S. Here is a section of tracks that were recently uncovered. Can you answer the following questions? •What is the size and nature of the organisms? •Were the tracks made at the same time? •How many animals were involved? •Can you reconstruct the events that occurred? •In what direction did the animals move? •Did they change speed or direction? •Was the soil moist or dry? The following summer some more digging revealed more of the track. What additional information have you gained that allows you to refine your answers? •Were the tracks made at the same time? •How many animals were involved? •Can you reconstruct the events that occurred? •In what direction did the animals move? •Did they change speed or direction? In the final summer of the excavation one last part of the footprint trail was uncovered. Does this section provide additional information to refine your hypothesis? So what happened? Who’s explanation is right? The fossil record provides us with the facts of what organisms were present but not how they interacted with one another or their environment. Evidence of Evolution –Comparative Biochemistry & Molecular Biology Comparative Biochemistry & Molecular Biology All organisms from bacteria to humans share many of the same biochemical details. The genetic code for protein-coding genes is nearly universal in eukaryotes and prokaryotes. All organisms use ATP as an important energy carrier. Similarly, the plasma membranes of all organisms, eukaryotic and prokaryotic, are structurally similar, consisting of a phospholipid bi-layer. # of amino acid differences between human hemoglobin and other organisms. Human DNA Compared to other Primates If humans and chimps are more closely related (=have had a common ancestor more recently), then we would expect the DNA sequences of humans and chimps to be more similar as well. Three phylogenetic trees were reconstructed based on the DNA sequences of: (a) 4700 bp of mitochondrial DNA, (b) the testis specific protein on the Y chromosome, (c) noncoding regions of the -globin gene. Evidence for Evolution - Comparative Morphology Homologous Structures Homologous structures are parts of different organisms, often quite dissimilar, that develop from the same ancestral part. All vertebrates contain a similar pattern of organs, suggesting that they are related to each other. The forelimbs of all mammals contain the same pattern of bones, although the bones now carry out a variety of functions. Ex: horse leg, bat wing, human arm, whale flipper Homologous structures teach us an important lesson about evolution: Evolution works primarily by modifying pre-existing structures. Even when two species function in completely different ways, they often use homologous structures to carry out those functions. All tetrapods (four legged) have limbs with five digits, at least at some stage in development. Certain tetrapods lose some of these digits during development, as in the bird wing shown here. But if the bird wing does not need five digits, why do five initially develop in the growing embryo? The most plausible explanation is that while the five digits are not functionally necessary, they represent a genetic artifact inherited from the ancestors of birds. Analogous Structures Analogous structures have similar form & function, but are structurally quite different Evidence for Evolution – Vestigial Structures Vestigial Structures Many organisms contain structures that have no function but that resemble functional structures of other organisms. This suggests that the structures are inherited from a common ancestor. Humans posses a complete web of muscles for wiggling their ears just as a coyote does. Humans have an appendix that seems to have no apparent function (although we may have needed it in the past to digest food). Whales & snakes contain pelvic bones just as humans do, but they serve no function. Evidence for Evolution - Comparative Embryology Embryo Development During development, organisms may exhibit characteristics of other organisms. This suggests that these organisms are related to other forms. The human embryo exhibits characteristics of the embryos of its ancestors. Early in their development, embryos posses gill slits like those of fish. Later in development, the embryos develop a tail. Human fetuses have a fine fur (lanugo) during the fifth month of development Evidence for Microevolution Evolution Observed Evolution of pesticide resistance in response to selection. Evidence for Evolution – Evolution Observed Evolution of drug-resistance in HIV