Retirement can be a jarring transition from a lifetime of extreme busyness. What does our evolutionary history say about which is better for us: working hard or taking it easy?

The Predator-Prey Divide

There is no single rule about how active animals should be for their health and reproductive success. It depends on how they make a living. Predators work little and spend long hours sleeping in the shade. Prey animals are essentially the opposite. If they are grass-eaters, they spend most of their day grazing and chewing the cud (if they are ruminants). The reason is that meat is a high-energy food whereas grass, and other herbs, are low on energy and high on fiber. This translates into long hours of chewing and digesting, leaving little time for sleep.

As hunter-gatherers, humans are both predators and vegetarians. So one might expect our normal activity level to be intermediate between predators like lions and prey like sheep. Lions typically sleep for about 16 hours a day, whereas sheep typically rest for about six to eight hours per day.

As both meat-eating predators and vegetarians, humans have a mixed activity schedule. We sleep for about eight hours, which is more than a sheep but a lot less than a lion.

The (Sad) History of Work

Humans have been extremely busy since the Industrial Revolution. The development of artificial light meant that........

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