The consequence of this evolutionary adaptation is that newborn human babies are more vulnerable and undeveloped. The bones of the skull grow and fuse together during the first year of life, which means that human babies are extremely vulnerable during this time and in need of a lot of protection and nurturing.
ACTIVITY
Summarize the benefits and disadvantages of bipedalism for humans.
Hairless bodies and sweating
Another way in which humans are different from other primates is in having a largely hairless body, along with a very efficient set of sweat glands that allow the regulation of body temperature, as opposed to panting, like many other mammals. Humans are the only primate species that has mostly naked skin. However, scientists are still trying to find out which hominins were the first to have lost their body hair. If the advantage of naked skin was the ability to regulate body temperature in the open environment of the savannah, in contrast to the more shaded forests where apes live, then our naked skin may have evolved million years ago.
The brain
One of the most significant differences between humans and other primates is that humans have a much larger brain. The modern human brain is three times larger in volume than that of the great ape. But it is not just the size of the human brain that is significant; it is the complex functional and cognitive abilities the brain engenders. However, a larger brain is also a more expensive brain. The human brain to body size ratio is significantly greater than in other species, and as a result the human brain requires 20 per cent of the energy used by the body, which is more than any other organ. The evolution of a larger brain suggests that a higher energy diet had also to evolve as a condition. Although the hominin lineage is over 6 million years old, brain size shows significant increases only from the time of Homo erectus, less than 2 million years ago. It was also around that time that we find evidence of a dramatic change in diet towards increased meat eating, more extensive use and manufacture of stone tools, and reduction in jaw and tooth size.
Large, complex brains can process and store a lot of information. This was a big advantage to early humans in their social interactions and encounters with unfamiliar habitats. Having a larger brain enabled modern humans to have much more complex forms of verbal communication than any other primate species. Humans are the only animal to create and use symbols as a means of communication. Humans also have more varied and complex social organizations. The most distinctive feature of humans is our mental ability to create new ideas and complex technologies, which has proved to be invaluable in the competition for survival. Another striking capability that derives from a larger and more effective brain is the ability to know what others might be thinking. In psychology, this is known as having a ‘theory of mind’.
Steven Mithen, an archaeologist, suggests that human forms of intelligence fall into four categories – social, technical, linguistic and natural history – which, once combined, led to the creation of consciousness. Having consciousness means having self-awareness, a sense of past and present.
However, the great apes are also surprisingly intelligent, having mental levels equivalent to a 3–4-year-old human child. This is sufficient to allow them to learn and use the sign language of deaf humans in at least a simplistic way. But, despite this, they do not have the capability of producing human speech and language.
Females live beyond the menopause
There is one additional interesting difference between humans and all other primates that is worth noting. At around the age of 50, human females go through the menopause and become sterile. Even in societies where life expectancy is low on account of the absence of medical care, such as those of hunter-gatherers, women often live for decades after ceasing to reproduce in their late forties or early fifties. In contrast, female chimpanzees, gorillas and other nonhuman primates usually remain capable of conception and giving birth even when they are older.
One explanation for this difference in humans is that living for some years following the menopause has proved to have natural selection value for our species. Having raised their own children, post-menopausal women around the world often take care of their grandchildren while their daughters are working. It is argued that this additional experienced and caring attention increases the chances that the grandchildren will survive to adulthood. The role of grandmothers in human societies is another example of cooperation in our species.
Cultural Evolution
Despite the many physiological and behavioural features that differentiate humans from apes, it is culture that separates us from all other species. Since culture allowed humans to transform the surrounding environment, we have to a large extent ceased to evolve any further physically. While some other animals show evidence of some form of culture, no species other than humans has such a complex and well-developed culture.
Cooking
There is evidence that the human brain became larger as a result of increased nutrition. One interesting argument put forward by Richard Wrangham (2009) is that cooking food – behaviour unique to humans – played a large role in our evolution. Around 800,000 years ago, early humans gathered around campfires that they made and controlled. There may have been lots of different reasons for this, including socialization, comfort and warmth, to share food and information, and to find safety from predators. Wrangham argued that the habit of eating cooked rather than raw meat permitted the digestive tract to shrink and the human brain to grow, since cooked meat is easier to digest and gives out more calories.
ACTIVITY
Give three reasons why cooking was so significant in human evolution.
Language
Spoken language is essential to modern human cultures. We use language to communicate in a complex, ever-changing world. It is very difficult to assess when language developed, as there is little fossil evidence relating to language. It is currently believed that language first appeared in the form of gestures around the time of Homo erectus, in association with our larger brains and the higher cognitive requirements of hunting in groups. Spoken language, on the other hand, may be a much more recent adaptation. There are various theories about why and how language developed (some will be discussed later in the book). However, anthropologists estimate that spoken language developed around 100,000 years ago. This is because objects involving complex behaviours that probably required language began to be made. Being able to use a language undoubtedly contributed to, and was a result of, greater self-awareness in human beings.
Symbols
Language is only possible because humans are able to think symbolically. Malinowski (1939: 955) pointed out that ‘symbolism must make its appearance with the earliest appearance of human culture’. The use of symbols (something used to represent an idea or object) changed the way that humans lived and provided new means of communicating and coping in an unpredictable world. The ability to use symbols and communicate helped humans to pass on information, cooperate and generally become more efficient and survive.
symbol Something which is used to represent an idea or object