Anatomy

Human body types vary substantially. Although body size is largely determined by genes, it is also significantly influenced by environmental factors such as diet and exercise. The average height of an adult human is about 1.5 to 1.8 m (5 to 6 feet) tall, although this varies significantly from place to place and depending on ethnic origin. The average mass of an adult human is 54–64 kg (120–140 lbs) for females and 76–83 kg (168–183 lbs) for males. Weight can also vary greatly (e.g. obesity). Unlike most other primates, humans are capable of fully bipedallocomotion, thus leaving their arms available for manipulating objects using their hands, aided especially by opposable thumbs.

Although humans appear hairless compared to other primates, with notable hair growth occurring chiefly on the top of the head, underarms and pubic area, the average human has more hair follicles on his or her body than the average chimpanzee. The main distinction is that human hairs are shorter, finer, and less heavily pigmented than the average chimpanzee's, thus making them harder to see.

The hue of human skin and hair is determined by the presence of pigments called melanins. Human skin hues can range from very dark brown to very pale pink. Human hair ranges from white to brown to red to most commonly black. This depends on the amount of melanin (an effective sun blocking pigment) in the skin and hair, with hair melanin concentrations in hair fading with increased age, leading to grey or even white hair. Most researchers believe that skin darkening was an adaptation that evolved as a protection against ultraviolet solar radiation. However, more recently it has been argued that particular skin colors are an adaptation to balance folate, which is destroyed by ultraviolet radiation, and vitamin D, which requires sunlight to form.The skin pigmentation of contemporary humans is geographically stratified, and in general correlates with the level of ultraviolet radiation. Human skin also has a capacity to darken (sun tanning) in response to exposure to ultraviolet radiation. Humans tend to be physically weaker than other similarly sized primates, with young, conditioned male humans having been shown to be unable to match the strength of female orangutanswhich are at least three times stronger.

The construction of the human pelvis differs from other primates, as do the toes. As a result, humans are slower for short distances than most other animals, but are among the best long-distance runners in the animal kingdom. Humans' thinner body hair and more productive sweat glands also helps avoid heat exhaustion while running for long distances. For this reason persistence hunting was most likely a very successful strategy for early humans - in this method, prey is chased until it is literally exhausted. This may have also helped the early human Cro-Magnon population out-compete theNeanderthal population for food. The otherwise physically stronger Neanderthal would have much greater difficulty hunting in this way, and much more likely hunted larger game in close quarters. A trade-off for these advantages of the modern human pelvis is that childbirth is more difficult and dangerous.

The construction of modern human shoulders enable throwing weapons, which also were much more difficult or even impossible for Neanderthal competitors to use effectively