mammals that sleep more have more immune cells and fewer parasites.

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Living World / Infectious Diseases
The New Theory About Why Animals Sleep: to Maintain the Immune System
New study shows that mammals that sleep more have more immune cells and fewer parasites.

by Amy Barth
From the April 2009 issue, published online March 22, 2009

Why do we sleep? An international team of researchers recently published evidence that slumber may have evolved to protect animals from dis*ease. They examined sleep patterns of more than 30 mammalian species—including hedgehogs, baboons, seals, and elephants—along with the strength of their immune systems and levels of parasite infection. Some animals, such as giraffes, doze for just a few hours a day; others, such as armadillos, snooze for 20 hours.

The study found that animals that sleep the longest had six times as many immune cells as those that take short siestas. Additionally, critters catching the fewest z’s had 24 times as many parasites as the best-rested species. “Maintaining the immune system may be the reason sleep has evolved,” says lead researcher Brian Preston, an evolutionary ecologist at the Max Planck Institute for Evolutionary Anthropology in Germany.

The New Theory About Why Animals Sleep: to Maintain the Immune System | Infectious Diseases | DISCOVER Magazine