toli, Ta toli, Ta

Longgupo, China?

Java, Indonesia

Sterkfontein, Swartkrans,'. South Africa 08 South Africa

Java, Indonesia

O Homo erectus o Homo habilis OAustralopithecines

AFRICAN EXODUS began as soon as H. erectus evolved, around 1.8 million years ago, probably in part because it needed a larger home range than that of its smaller-bodied predecessors.

mands for as long as they did speaks to their skills as foragers [see box on preceding page].

Modern Quandaries

JUST AS pressures to improve dietary quality influenced early human evolution, so, too, have these factors played a crucial role in the more recent increases in population size. Innovations such as cooking, agriculture and even aspects of modern food technology can all be considered tactics for boosting the quality of the human diet. Cooking, for one, augmented the energy available in wild plant foods [see box on page 68]. With the advent of agriculture, humans began to manipulate marginal plant species to increase their productivity, digestibility and nutritional content—essentially making plants more like animal foods. This kind of tinkering continues today, with genetic modification of crop species to make "better" fruits, vegetables

VARIOUS DIETS can satisfy human nutritional requirements. Some populations subsist almost entirely on plant foods; others eat mostly animal foods. Although Americans consume less meat than do a number of the traditionally living people described here, they have on average higher cholesterol levels and higher levels of obesity (as indicated by body mass index) because they consume more energy than they expend and eat meat that is higher in fat.

and grains. Similarly, the development of liquid nutritional supplements and meal replacement bars is a continuation of the trend that our ancient ancestors started: gaining as much nutritional return from our food in as little volume and with as little physical effort as possible.

Overall, that strategy has evidently worked: humans are here today and in record numbers to boot. But perhaps the strongest testament to the importance of energy- and nutrient-rich foods in human evolution lies in the observation that so many health concerns facing societies around the globe stem from deviations from the energy dynamic that our ancestors established. For children in rural populations of the developing world, low-quality diets lead to poor physical growth and high rates of mortality during early life. In these cases, the foods fed to youngsters during and after weaning are often not sufficiently dense in energy and nutrients to meet the high nutritional needs associated with this period of rapid growth and development. Although these children are typically similar in length and weight to their U.S. counterparts at birth, they are much shorter and lighter by the age of three, often resembling the smallest 2 to 3 percent of American children of the same age and sex.

In the industrial world, we are facing the opposite problem: rates of childhood and adult obesity are rising because the energy-rich foods we crave—notably those packed with fat and sugar—have become widely available and relatively in-


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