The evolution of human intelligence refers to a set of theories that attempt to explain how human intelligence has evolved.
These theories are closely tied to the evolution of the human brain and to the emergence of human language. The timeline of human evolution spans approximately 7 million years, from the separation of the Pan genus until the emergence of behavioral modernity by 50,000 years ago. The first 3 million years of this timeline concern Sahelanthropus, the following 2 million concern Australopithecus and the final 2 million span the history of actual human species (the Paleolithic). Many traits of human intelligence, such as empathy, theory of mind, mourning, ritual, and the use of symbols and tools, are already apparent in great apes although in lesser sophistication than in humans.
The great apes show considerable abilities for cognition and empathy. Chimpanzees make tools and use them to acquire foods and for social displays; they have sophisticated hunting strategies requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can learn to use symbols and understand aspects of human language including some relational syntax, concepts of number and numerical sequence.In one study, young chimpanzees outperformed human college students in tasks requiring remembering numbers. This claim was refuted in a later study after it was noted that the chimpanzees had received extensive practice with the task while the students were evaluated on their first attempt. When human subjects were given time to practice, they substantially outperformed the young chimps.
Chimpanzees are capable of empathy, having been observed to feed turtles in the wild, and show curiosity in wildlife (such as pythons).Homininae Around 10 million years ago, the Earth’s climate entered a cooler and drier phase, which led eventually to the ice ages beginning some 2.6 million years ago. One consequence of this was that the north African tropical forest began to retreat, being replaced first by open grasslands and eventually by desert (the modern Sahara). As their environment changed from continuous forest to patches of forest separated by expanses of grassland, some primates adapted to a partly or fully ground-dwelling life. Here they were exposed to predators, such as the big cats, from whom they had previously been safe.
These environmental pressures caused selection to favor bipedalism: walking on hind legs. This gave the Homininae’s eyes greater elevation, the ability to see approaching danger further off, and a more efficient means of locomotion (see main article for details). It also freed the forelimbs (arms) from the task of walking and made the hands available for tasks such as gathering food.
At some point the bipedal primates developed handedness, giving them the ability to pick up sticks, bones and stones and use them as weapons, or as tools for tasks such as killing smaller animals, cracking nuts, or cutting up carcasses. In other words, these primates developed the use of primitive technology. Bipedal tool-using primates form the Hominina subtribe, of which the earliest species, such as Sahelanthropus tchadensis, date to about 7 to 5 million years ago. From about 5 million years ago, the Hominin brain began to develop rapidly in both size and differentiation of function.
It has been shown that Great Ape cooperation and communication is severely impeded by their competitiveness, and thus that the apes would revolutionize their culture-bearing ability if they could just shrug off their competitiveness. It is also well known that even early hominins lacked the size and sharpness of their canine teeth that apes use as a threat signal, suggesting prehumans simply had no use for threat signals. That means they had already transcended ape competitiveness and thus developed superior cooperation and communication.
There has been a gradual increase in brain volume as humans progressed along the timeline of evolution (see Homininae), starting from about 600 cm3 in Homo habilis up to 1500 cm3 in Homo sapiens neanderthalensis. Thus, in general there’s a correlation between brain volume and intelligence.
However, modern Homo sapiens have a brain volume slightly smaller (1250 cm3) than neanderthals, and the Flores hominids (Homo floresiensis), nicknamed hobbits, had a cranial capacity of about 380 cm3 (considered small for a chimpanzee) about a third of that of H. erectus. It is proposed that they evolved from H. erectus as a case of insular dwarfism. With their three times smaller brain the Flores hominids apparently used fire and made tools as sophisticated as those of their ancestor H.erectus. In this case, it seems that for intelligence, the structure of the brain is more important than its volume.
The social brain hypothesis was proposed by British anthropologist Robin Dunbar, who argues that human intelligence did not evolve primarily as a means to solve ecological problems, but rather intelligence evolved as a means of surviving and reproducing in large and complex social groups. Some of the behaviors associated with living in large groups include reciprocal altruism, deception and coalition formation. These group dynamics relate to Theory of Mind or the ability to understand the thoughts and emotions of others, though Dunbar himself admits in the same book that it is not the flocking itself that causes intelligence to evolve (as shown by ruminants).
Dunbar argues that when the size of a social group increases, the number of different relationships in the group may increase by orders of magnitude. Chimpanzees live in groups of about 50 individuals whereas humans typically have a social circle of about 150 people, which is now referred to as Dunbar’s number. According to the social brain hypothesis, when hominids started living in large groups, selection favored greater intelligence.
As evidence, Dunbar cites a relationship between neocortex size and group size of various mammals. However, meerkats have far more social relationships than their small brain capacity would suggest. Another hypothesis is that it is actually intelligence that causes social relationships to become more complex, because intelligent individuals are more difficult to learn to know. There are also studies that show that Dunbar’s number is not the upper limit of the number of social relationships in humans either