Species Preservation and Population Size: When Eight Is Not Enough

Scientists estimate that about 1000 nesting Kemp’s Ridley sea turtles (below left), 300 right whales (below middle), and 65 northern hairy-nosed wombats (below right) survive in the wild, to name just a few of the world’s endangered species.1 But what do those numbers mean? Are 65 hairy-nosed wombats enough to save a species teetering on the edge of extinction? Ignoring evolutionary history, one might answer, “Sure; as long as they can breed, we only need a few individuals to start a new population.” But evolutionary theory tells a different story.

According to evolutionary theory, very small populations face two dangers—inbreeding depression and low genetic variation—that might keep them from recovering, despite our best efforts to preserve them.

Sea Turtle Right Whale Hairy-nosed wombat
Kemp's Ridley sea turtle Right whale Hairy-nosed wombat


• Sea turtle photo courtesy of US Geological Survey
• Right whale photo courtesy of NOAA
• Hairy-nosed wombat photo courtesy of Government of South Australia, South Australia Central Team
1 According to US Fish and Wildlife Service, 2002.

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Inbreeding Depression

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