Diet and the evolution of modern human form in the Middle East.

Fully modern human form more gracile than the antecedent archaic modern form was evident by 30,000 years ago. One hypothesis to explain this decrease in skeletal robustness is that change occurred in human diet and that this change was associated with a decrease in activity levels required in both individual and group behavior. It is possible to study dietary change directly using trace element analysis of strontium levels in bone. The amount of strontium in bone reflects the amount of strontium in diet. Since plants contain higher levels of strontium than do animal soft tissues, the level of bone strontium will differ between individuals according to the proportion of plant and animal products in their diets. In this study the ratio of strontium:calcium in human bone to strontium:calcium in faunal bone is compared for samples of archaic modern humans (from Mugharet et Tabun, Mugharet es-Skhul, and Jebel Qafzeh) and fully modrn humans from Mugharet el-Kebara and Mugharet el-Wad) from Israel. The use of a ratio controls for potentially unequal strontium levels in soils at different sites and for different diagenetic histories between sites. The results of the analysis are internally reliable, reflecting bone strontium levels rather than technique error; therefore, they reflect diet. It appears that a change occurred in the amount of animal protein in the diet of humans but that this change occurred almost 20,000 years after the first appearance of skeletally modern humans. These results refute the hypothesis that the morphological transformation to modern human form occurred as a result of behavioral changes involved in obtaining previously unused foods. If any decrease in human activity level occurred between archaic modern and fully modern humans, this decrease probably was due to alterations in the means of procuring or processing the same kinds of foods that had been utilized earlier in time.