Page "Volcanic winter" Paragraph 14

The causes of the bottleneck phenomenon — i. e., a sharp decrease in a species ' population, immediately followed by a period of great genetic divergence ( differentiation ) among survivors — is attributed to volcanic winters by some researchers.

According to anthropologist Stanley Ambrose, such events diminish populations to " levels low enough for evolutionary changes, which occur much faster in small populations, to produce rapid population differentiation ".

With the Toba bottleneck, many species show massive effects of narrowing of the gene pool, and it is believed Toba nearly exterminated humankind.