The Story of the Human Body

Hominin eating habits underwent significant change during the evolution of australopiths. Fossil evidence shows that australopiths lived in Africa from 4 to 1 million years ago, and several species have been identified. They are divided into two groups: gracile and robust. Gracile australopiths include Au. afarensis, Au. africanus, Au. sediba, Au. anamensis, and Au. garhi, and robust include Au. boisei, Au. robustus, and Au. aethiopicus. Lucy, a 3.2-million-year-old Au. afarensis found in Ethiopia, is the best-known representative.

Australopiths looked like bipedal chimps; they had small brains, long snouts, thick brow ridges, short legs, long and powerful arms, and they reproduced similar to modern apes, taking 12 years to mature and reproducing every 5 years. Australopiths likely relied on tougher foods, like tubers, stems, and seeds, explaining their larger teeth, jaws, faces, and chewing muscles. They had wide hips, arched feet, and short big toes, suggesting their gaits were more similar to humans’ gaits; however, some species, like Au. sediba, retained traits beneficial for climbing.

The climate changed during the australopiths’ reign, and Africa became cooler and drier with more woodland and savanna habitats, limiting the amount of available fruit and increasing australopiths’ reliance on fallback foods, or less desirable foods. Australopiths learned to dig for underground foods, or underground storage organs (USOs), like tubers. Eating USOs, which are nutrient- and energy-dense, may have allowed australopiths to expand their populations. This is extrapolated though australopiths’ physical features like their flat molars and the bony ridges in their skulls which are thought to accommodate powerful jaw muscles.

Australopiths lived in woodlands and grasslands, and they traveled long distances in their daily foraging. While some experts think australopiths walked similarly to chimpanzees, Lieberman argues that australopiths show signs of human-like pendular walking—a pattern of walking that conserves energy by creating pendular forces while walking. Such evidence includes short, in-line big toes, a partial foot arch, large, flat heel bones, straighter legs, large hip and knee joints, stable ankles, and adaptations suggesting they could stabilize their upper bodies while walking. These traits, along with fossilized footprints in Laetoli, Tanzania, suggest australopiths were relatively efficient walkers. Australopiths may have had the ability to sweat, which would have helped them travel during the heat of the day when predators were less active.

Although distant ancestors, australopiths offer insight into modern human biology as humans would not exist without these early ancestors, and modern humans possess several traits in common with australopiths.

While modern humans should be concerned about human-caused climate change, hominins have survived multiple bouts of natural climate change. Climate change spurs evolution by making food more challenging to obtain. Hominins became more human-like 2 million years ago at the start of the Ice Age. African hominins were subject to drastic environmental and geological changes, which encouraged adaptations for traveling longer distances, eating tougher foods, hunting and gathering, and tool-making.

Homo erectus, discovered in 1890 in Indonesia and later found in China, Tanzania, Morocco, and Algeria, provides insight into the emergence of hunter-gatherer lifestyles. The species evolved 1.9 million years ago in Africa, then dispersed into other areas. It was variable in height and weight and similar in appearance to Homo sapiens. Other species in the Homo genus include H. habilis, H. rudolfensis, and H. neanderthalensis.

Two critical stages of evolution occurred in early Homo: H. habilis evolved larger brains and smaller snouts, and H. erectus evolved human-like legs, feet, arms, and teeth and larger brains than H. habilis. H. erectus had human-like behaviors, including hunter-gatherer social systems, defined by four behaviors: “gathering plant foods, hunting for meat, intensive cooperation, and food processing” (72).

By studying living hunter-gatherers, researchers infer that earlier species, particularly mothers, could not obtain enough calories through gathering. Hominins became omnivorous 2.6 million years ago, marking the sex-division of labor, as mothers could not hunt while caring for young offspring. Dividing labor requires food-sharing behaviors; modern hunter-gatherers practice marriage, and men hunt while women gather. Food sharing behaviors occur between extended family and community members, and such societies are egalitarian. Early hominins processed foods to make them easier to eat. The oldest food-processing tools were knife-like stones called Oldowan tools. Food processing reduced the time and energy spent eating and increased the amounts of calories and nutrition extracted during digestion. Food sharing and processing is unique to hominins.

Experts assume early Homo traveled about as much as modern hunter-gatherers—five to nine miles a day. This need to travel prompted adaptations like longer legs, arched feet, strong leg bones and joints, less surface area exposed to the sun while walking, the ability to sweat, and projecting noses that regulate the humidity and temperature of inhaled air. Researchers speculate that early Homo relied on endurance to persistent hunt, or to chase prey over long distances. This is inferred through fossilized traits—nuchal ligament, gyroscopic inner ear canals, short toes, narrow waists, and wide shoulders. Experts also infer early Homo had little or no fur and could sweat, but this cannot be confirmed through fossil records.

Hand adaptations, including increased flexibility and movement, allowed early Homo to make and use tools for obtaining and processing food. Processing foods may have led to the development of smaller molars and “snoutless” faces. Hunting and gathering led to gut adaptations. The human gut uses about as much energy as the brain and is sometimes called the “second brain.” Compared to other mammals, humans have small guts, which may be because hominins adopted more nutrient-dense diets, increasing the efficiency of digestion and allowing energy to be diverted to the brain.

Lieberman asserts that his speculations are reliable because they are based on fossil evidence and living humans. He cites examples of people—Alexander Selkirk and Marguerite de La Rocque—becoming stranded on desert islands, which emphasizes humans’ evolved survival capabilities.