Evolution of human intelligence

The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately 7 million years, from the separation of the genus Pan 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 the genus Homo in the Paleolithic era. The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately 7 million years, from the separation of the genus Pan 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 the genus Homo in the Paleolithic era. Many traits of human intelligence, such as empathy, theory of mind, mourning, ritual, and the use of symbols and tools, are apparent in great apes although in less sophisticated forms than found in humans, such as great ape language. The great apes (hominidae) show considerable cognitive and empathic abilities. Chimpanzees can 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. Around 10 million years ago, the Earth's climate entered a cooler and drier phase, which led eventually to the Quaternary glaciation 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. It also freed the 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.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 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. Roughly 2.4 million years ago Homo habilis had appeared in East Africa: the first known human species, and the first known to make stone tools, yet the disputed findings of signs of tool use from even earlier ages and from the vicinity as multiple Australopithecus fossils may put this to question its 'greater intelligence when compared to earlier and more primitive Australopithecus genus'. The use of tools conferred a crucial evolutionary advantage, and required a larger and more sophisticated brain to co-ordinate the fine hand movements required for this task. Our knowledge of the complexity of behaviour of Homo habilis is not limited to stone culture, they also had habitual therapic use of toothpicks.The evolution of a larger brain created a problem for early humans, however. A larger brain requires a larger skull, and thus requires the female to have a wider birth canal for the newborn's larger skull to pass through. But if the female's birth canal grew too wide, her pelvis would be so wide that she would lose the ability to run, which was a necessary skill 2 million years ago. The solution to this was to give birth at an early stage of fetal development, before the skull grew too large to pass through the birth canal. This adaptation enabled the human brain to continue to grow, but it imposed a new discipline. The need to care for helpless infants for long periods of time forced humans to become less mobile. Human bands increasingly stayed in one place for long periods, so that females could care for infants, while males hunted food and fought with other bands that competed for food sources. As a result, humans became even more dependent on tool-making to compete with other animals and other humans, and relied less on body size and strength.