Do catastrophic events have any affect on human populations?

Something like the recent Earthquake in China, or for a more extreme example the Black Death in Europe, kill off a large number of the population. Are such events selective enough about who lives and dies that they can alter the genetics of the population?

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995