lecture 2 evidence for evolution

lecture 2 evidence for evolution - If organisms have...

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Unformatted text preview: If organisms have evolved through descent with modification, as Darwin proposed, which of the following patterns is expected in the fossil record? A. Taxonomic groups should be distributed randomly in time. B. Taxonomic groups should be distributed randomly in space. C. The most ancient fossil assemblages should include all the major groups found in modern faunas. D. Fossils of simple organisms (e.g., bacteria) should appear in the geological record before fossils of complex organisms (e.g., mammals). CLICKER QUESTION Since the beginning of the fossil record, many new life forms have appeared, and most old forms have disappeared. The many traceable sequences of changing anatomical forms, inferred from ages of rock layers, convince scientists that the accumulation of differences from one generation to the next has led eventually to species as different from one another as bacteria are from elephants. Evolution in the News Fossilized orchid pollen on the back of a bee preserved in amber has offered the first evidence that these delicate flowers existed around the time of the dinosaurs, U.S. researchers said on Wednesday. While orchids are the largest and most diverse plant family on Earth, they have been absent from the fossil record. The fossil record lacks evidence of orchids because they bloom infrequently and are concentrated in tropical areas where heat and humidity prevent fossilization. Their pollen is dispersed only by animals, not wind, and disintegrates upon contact with the acid used to extract pollen from rocks. Orchids ambiguous fossil record has fed a longstanding debate over their age, with various scientists pegging the family at anywhere from 26 to 112 million years old. Those arguing for a younger age have often pointed to the lack of a meaningful fossil record as evidence of the familys youth, along with the highly specialized flowers need for a well-developed array of existing pollinators to survive. Proponents of an older age for orchids had cited their ubiquity around the world, their close evolutionary kinship with the ancient asparagus family, and their bewildering diversity: Some 20,000 to 30,000 species strong, the showy plants comprise some 8 percent of all flowering species worldwide. Encased in a block of amber, the remains of an extinct, stingless bee (Proplebeia dominicana) with a clump of orchid pollen stuck to its back indicate the flowering plants arose some 76 million to 84 million years ago, much sooner than many scientists had estimated. The extinct bee they studied, preserved in amber with a mass of orchid pollen on its back, represents some of the only direct evidence of pollination in the fossil record. To estimate the ages of the major branches of the orchid family, they compared DNA from the pollen sample with DNA from other orchid species. The so-called molecular-clock method is based on an idea that differences between the DNA molecules of particular species is a measure of how long the two groups have been evolving independent of one another. Our analysis places orchids far toward the older end of the range that had been...
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This note was uploaded on 03/19/2008 for the course BIOL 101 taught by Professor Annestork during the Fall '08 term at Ithaca College.

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lecture 2 evidence for evolution - If organisms have...

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