Being Human

Although not known for their generosity, chimpanzees do regularly share food. Most chimpanzee food sharing does not involve actively handing food to someone else, but rather passively allowing another individual to take it. Aware of this possibility, chimpanzees often beg for food from those who have it – holding out a hand or even reaching toward another’s mouth as he chews. Foods that are shared are those that are high-value, monopolizable, and rare, such as meat, honey, or large fruits. Food sharing appears to strengthen social bonds in chimpanzees.

Chimpanzees live in rainforest habitats where the rainy season brings regular thunderstorms. But these African apes make little attempt to stay dry in the rain. They often huddle miserably and simply get wet. Sometimes though, chimpanzees perform what researchers call “rain dances”: vigorous yet deliberate physical and auditory displays. Male chimpanzees charge through the forest, rhythmically swaggering, drumming their feet on tree buttresses, slapping the ground, breaking and dragging vegetation, and making loud vocalizations.

You’ve heard of the TV series Arrested Development, but did you know that arrested development is also an evolved reproductive strategy for some male orangutans? Adult males of this red-haired Indonesian ape species typically develop a massive size accompanied by beards, throat sacs, and protruding cheek flanges. A mature male orangutan is the primary mating partner of several females in his home range and is aggressive toward intruder males. This polygynous mating pattern leaves many males without ranges.

Gorillas are the largest-bodied primates living today. Adult male gorillas are called silverbacks, due to the silvery hair that develops across their backs with maturity. Silverbacks in the wild stand 5½ - 6 feet tall when on two legs and weigh more than 350 lbs. Female gorillas are considerably smaller – only about half the size of males. Gorillas typically form polygynous groups, including a dominant silverback and several females with offspring. Because the sex ratio at birth is 50:50, this leaves a lot of males without a group of females.

Since the discovery of Neandertal remains in Europe in 1829, scientists have been fascinated by the relationship of Neandertals to modern humans. One question involves whether they communicated through spoken language. Because language doesn’t fossilize, we rely on indirect data. DNA analysis reveals that Neandertals had the human form of the FOXP2 gene, associated with our ability to comprehend grammar and control the mouth movements used in speech. Another clue comes in the form of the hyoid bone, a small horseshoe-shaped bone that supports the muscles involved in sound production.

Do your children sometimes seem to outgrow their clothes or shoes overnight? Research by anthropologist and physician Michelle Lampl has confirmed this conventional wisdom about growth spurts. Children do not grow continuously but rather get taller in brief, rapid periods, likely while they sleep, sometimes growing more than half an inch in a single night. The growing pains that wake some children at night may occur during such spurts. Infants appear to need extra sleep during their growth spurts, explaining some of the irregularity in infant sleep patterns that often frustrates parents.

In polygynous primate species, males tend to be larger than females, and this sex difference in body size is evident starting very early in life. In humans, for example, boys are (on average) heavier than girls from birth. Anthropologist Katie Hinde thus suspected that nursing mothers may produce milk differently for sons vs. daughters. She investigated this hypothesis by examining the energy density and quantity of milk produced by captive rhesus macaques.