"Humans apparently share with most primates a tendency to increase the proportion of dietary animal matter whenever it is economical to do so... Only religious beliefs or perception of the health hazards of high meat diets will inhibit those with access to luxury diets from developing and maintaining meat consumption at health-hazard levels briefly attainable by our primate predecessors and hominid ancestors."

The popularity of the Atkins Diet is easily understood from the perspective of this little known publication from 1978 conceived by my mentor at the University of California at Davis, Bill Hamilton. Drawing heavily from our own observations of baboons and chimpanzees eating insects and meat, Bill and I concluded that the strong preference of humans for meat and other animal products is a legacy of our omnivorous primate heritage. The Atkins Diet, and others emphasizing animal products as opposed to plant products, was a stroke of genius: encourage people to eat the foods that we and our ancestors have savored for the past many millions of years.

The problem, at least for chimpanzees and baboons, is that their favorite insect foods are available in outbreak quantities for only a few days per year. Another favorite food, infant antelope, is also available only seasonally. Other prey animals, like young colobus monkeys for chimpanzees, are not easily captured and are not available in substantial numbers. Thus, insects and meat - although highly-desired food items for chimpanzees and baboons - typically account for less than 5% of their diets.

One of Bill's many insights was that the potential for primates like baboons to expand their consumption of meat is constrained by their very social organization. These monkeys live in groups averaging from 50 to 75 individuals that have consistant dominance relationships in terms of who has priority of access to resources. Any subordinate individual who captures an infant impala, for example, would almost certainly have it taken away by a higher-ranking group member. Thus, the benefits of hunting are minimal except for the highest ranking group members.

Humans, on the other hand, have overcome the physical, economical, and social limitations that constrain the capacity of our close primate relatives to eat meat. According to a 1971 United Nations report that Bill and I cited, humans get an average of 14.8.% of their calories from animal products. This value shoots up to 40% in the United States and to over 50% in New Zealand, which has an almost limitless supply of inexpensive meat.

To what extent, if any, has the human physiology adapted to the relatively recent surge in meat consumption that probably coincided with the domestication of animals? Unfortunately, epidemiologic and biomedical studies suggest that the human body is not ideally suited to diets high in animal products. Even in 1978 high-meat diets had been linked to cancer of the colon as well as to atherosclerosis. More recently, reseachers have also suggested ties between cholesterol and diseases as diverse as prostate cancer and Alzheimer's.

So what is an ideal diet for humans? Bill calls it the "evolutionarily-relevant diet," one that resembles that of our early ancestors and to which our digestive tracts are adapted. Studies of nonhuman primates, hominid archeological sites, and contemporary human hunter-gatherer societies converge on a diet high in grains, tubers, fruits, and vegetables - and also the occasional eggs and portions of meat.

Several of my friends swear by the Atkins Diet. Yes, they have lost weight, but I often wonder at what long-term risk to their health? I too enjoy a medium-rare steak, but I try to follow Bill Hamilton's guidelines for an "evolutionarily-relevant diet," which calls for eating meat and other animal products in moderation, as do the baboons and chimpanzees that we watched in Africa.