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Light at 38 M.P.H. - Another Fine Mess - Sleuthing the Genes - Paleolithic Fast Food - E-mail and Web Information


Paleolithic Fast Food

Hayonim Cave, Israel, which sheltered early humans for 200,000 years, opens onto an inland valley in the Western Galilee. The Mediterranean Sea is visible in the background. Photograph by Ofer Bar-Yosef

To a cave-dwelling human 50,000 years ago, "fast food" meant just the opposite: something slow-moving and easy to catch. Now archaeologists have devised a clever way to extrapolate from the detritus of ancient meals a measure of prehistoric population size and its growth rate. Their findings suggest early human populations were much smaller than had previously been supposed.

Since 1982, MacCurdy professor of prehistoric archaeology Ofer Bar-Yosef and his colleagues have been excavating three caves in north coastal Israel--Kebara, Qafzeh, and Hayonim. Taken together, the caves yield data covering the period from 200,000 to 10,000 years ago. Recently, zooarchaeologist Mary Stiner of the University of Arizona, working with Bar-Yosef and others, has gleaned fresh insights from the shells and bones found in early human trash heaps.

The archaeologists made two important discoveries. First, they found that as they dug deeper into the past, slow-moving prey like tortoises and shellfish constituted a greater proportion of the human diet. Not until the Upper Paleolithic period (44,000 to 19,000 years ago) did the consumption of fast-moving prey like hares and birds begin to increase steadily.

Excavations inside Hayonim Cave. The three-dimensional grid lets archaeologists place objects in time. Photograph by Ofer Bar-Yosef

Because capturing hares and birds requires the use of snares or other technological innovations, humans probably did not hunt such creatures until slow prey became hard to find. The growth of fast prey in the human diet over time therefore suggests that groups of hunter-gatherers competing for resources had proliferated to the point that they could no longer simply move on to another site, expecting to find untapped sources of easily captured food. Their subsistence territories would instead begin to infringe on those of other human groups who were competing for the same nutritional resources. "As you increase the numbers in your social groups, you may cross some kind of threshold," says Bar-Yosef. "Increasing population might have led to the development of the snare."

The second, related discovery made by the archaeologists was that the average size of the slow-moving prey was much smaller in more recent strata. A one-tortoise lunch 150,000 years ago would have been 50 percent larger than one 20,000 years ago. It's like the swordfish problem in New England today, Bar-Yosef says. "More people want fish, and so you deplete your resources. If the size is constantly decreasing, it means that you are eating too many of them. It's a constant problem in human evolution."

Chart by Stephen Anderson

Yet the archaeologists were surprised to find that for 100,000 years, human hunting did not noticeably diminish either the size or the relative abundance of slow prey at the cave sites. Tortoise populations plummet when a mere 7 percent have been eaten, due to a threshold effect. Yet half the animal remains from the early Middle Paleolithic (200,000 to 100,000 years ago) found at Hayonim were tortoises. At Kebara, a significant drop in tortoise size didn't occur until 30,000 years ago. The comparatively recent reductions in both size and relative abundance of slow prey in prehistoric diets serve to strengthen the hypothesis that early human populations were still small and mobile, spending little time foraging in any one area.

The findings support estimates made by geneticists, whose analysis of DNA from living peoples around the world indicates that prehistoric populations were small. Genetics-based data suggest that fewer than 10,000 people--not 100,000, as generally cited--inhabited sub-Saharan Africa 100,000 to 200,000 years ago, and that as few as 500 people, by one estimate, departed their homeland to colonize Eurasia.

~ Jonathan Shaw

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