Genetic drift

“Curse and Blessing of the Ghetto” by Jared Diamond

This article discusses the possible historical and evolutionary causes behind the modern prevalence of Tay-Sachs disease among Ashkenazim, or Eastern European, Jews. Diamond considers the founder effect, a form of genetic drift, as the cause for relatively high rates of the disease among Ashkenazim Jews, then argues that “it seems unlikely that genetic accidents would have pumped up the same gene not once but twice in the same population” (Diamond 1991:195). Instead, he speculates that the most plausible explanation for Tay-Sachs among the Ashkenazim population is that natural selection worked in favor of these genes because they provided some kind of protection from the strong presence of tuberculosis among the communities from which modern Ashkenazim Jews descend. If his hypothesis were true, then, in terms of natural selection, it would prove most advantageous to be heterozygous for Tay-Sachs. In other words, the risk of death posed by Tay-Sachs was smaller than the risk of death posed by tuberculosis for these populations at the time when this genetic disease increased in incidence.


Explain genetic drift and the founder effect. Site at least one example from the textbook that mirrors the example of Tay-Sachs, and elaborate on how it works to enhance survival for heterozygous individuals.


At the end of his article, Diamond points out the United States is in some ways a melting pot and in some ways it is not because “each ethnic group has some characteristic genes of its own” (Diamond 1991:197). Furthermore, sometimes these “characteristic genes” appear as genetic diseases that once worked to improve the survival rates among certain ethnic groups, but now, with the eradication (or near eradication) of many lethal diseases, they may cause more harm than good. How might the study of evolution intersect with modern medicine to assist us in diminishing the occurrence of devastating genetic diseases such as Tay-Sachs? What do you think the evolutionary implications might be of working to reduce or eliminate such diseases?

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