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A Natural Experiment to Test the Hypothesis That Loss of Genetic Variability was Responsible for Mass Extinctions of the Fossil Record

Animals living under "constant" environmental conditions have been hypothesized to lose genetic variability. If so, this would account for a lack of adaptation to changing environments and hence be responsible for the significant mass extinctions of the fossil record. However, eight modern deep-sea species (1,000-2,000 m) in as constant a major environment as exists on earth, have as much genetic variability as do shallow marine and terrestrial species (20%-50% of the loci polymorphic). Accordingly, species do not appear to lose genetic variability as the environment becomes "constant," and this explanation of the cause for mass extinction fails.