Nutritional ecology

Humans are omnivorous. Humans were eating wild plant foods from the origins of the subfamily Homininae about 6 mya until the inception of agriculture 11,000 years ago. Comparisons with omnivorous, widespread non-human primates such as baboons make it likely that the earliest hominins consumed a variety of plants and plant parts, and also consumed insects, eggs, and small animals like birds and hares. Bone chemistry analyzing stable carbon isotopes shows that South African australopithecines were omnivores. This is true even for the species Australopithecus robustus, which had been considered highly vegetarian since the mid-1950s. Neanderthal bone chemistry shows that these fossil humans were highly carnivorous, as one might expect, given that they lived in

Humans have domesticated other mammals, such as the cow (Bos taurus). (Photo by Paul Gun/Corbis. Reproduced by permission.)

A seven-week-old human embryo. (Photo by © Garvis Kerimian/Peter Arnold, Inc. Reproduced by permission.)

highly seasonal environments where carbohydrates were impoverished during certain periods. Humans lack the high complex molar teeth or ruminant stomachs that allow ungulates to process grass, and they lack the ability to detoxify secondary compounds in mature leaves or other plant parts. Only the advent of food processing or cooking technology allows humans to compensate for these biological restrictions, and to incorporate certain plants into their diets.

Cut-marks and percussion marks made by stone tools on animal bones show that vertebrate meat, fat, and marrow were incorporated into the hominin diet beginning at 2.5-2.6 mya. Tools are necessary to cut through the tough skin of a carcass, sever tendons and dismember a carcass, remove meat from bones, and break open bones to extract marrow. It is likely that hominins first acquired meat, fat, and marrow by scavenging carcasses brought down by large mammalian carnivores. By 1.8-1.6 mya, however, some archaeologists argue for the definite presence of either confrontational scavenging (where hominins displace large carnivores at a fresh and relatively intact carcass) or the hunting of vertebrate prey.

In 1968, the social anthropologist Marshall Sahlins famously described living hunter-gatherers as having the "Original Affluent Society." The depiction of hunter-gatherers as experiencing a leisurely and affluent lifestyle is no longer considered accurate. Detailed information on living hunter-gatherer groups shows that nutritional intake can be extremely variable between groups. Seasonal variation in total caloric intake or nutrient quality can be quite marked.

The domestication of animals and plants is a milestone in human history, and represents a fundamental difference in the human ability to alter ecosystems on a global scale. Animal and plant domestication occurs when humans intervene in the reproduction of other species. This intervention gradually becomes deliberate, and humans consciously select for certain phenotypic traits in the domesticated species. Dogs are the first domesticated species. Unequivocally domesticated dogs appear in the Natufian of the Middle East at 14,000 years ago. Goats, sheep, pigs, cattle, and donkeys follow. Evidence of farming first appears in the Middle East, about 11,000 years ago. Food crops have multiple centers of origin in both the New and Old Worlds.

The body mass index is widely used to study human body build and the relationship between nutrient intake and activity levels. This index is weight divided by height (BMI = kg/m2). A BMI of less than 18.5 indicates a chronic energy deficiency. Harsh environments increase the probability of insufficient calories, at least seasonally. The body mass index is rising in nearly all populations that are experiencing industrialization. This is caused by an ever more sedentary lifestyle, in which decreased physical activity is accompanied by an abundance of readily available, high calorie foods. As of 2003, this trend is becoming so pronounced, and has such deleterious health consequences, that many medical and governmental agencies are investigating ways to halt the increase in human obesity.

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