Unformatted text preview: Andra Stanley Paper #9, fixed RecitationTuesday, 3:00-3:50 Young, Chapter 7 Microscopial observations showed that cells made up plant and animal tissues; the cell was composed of an outer membrane, the enclosed cell contents, and the nucleus. Rudolph Virchow argued that cells can only come from the division of pre-existing cells. The nucleus contains the basis for heredity to be passed from one generation to the next, with the chromatin as the hereditary substance. The germ cells must be created by division without replication, enabling the germ cell to have only half the normal number of chromosomes, through the process of meiosis. Thus it was determined that the transmission of heritable traits was not related to the growth of the organism, and therefore variation was undirected. Weismann concluded that natural selection could be the only factor that could give direction to hereditary changes through evolution. Spencer disagreed, arguing that evidence was inconclusive and inheritance of acquired characteristics could also give...
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- Fall '06