Hominid intelligence
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The nature and origins of hominid intelligence is a much-studied and much-debated topic[citation needed], of natural interest to humans as the most successful and intelligent hominid species. There is no universally accepted definition of intelligence, one definition is "the ability to reason, plan, solve problems, think abstractly, comprehend ideas and language, and learn" (cf. article on intelligence).
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[edit] Evolutionary perspective
Human's early primate ancestors possessed these characteristics to no greater extent than other mammals such as rodents[citation needed]. Today one hominid species, homo sapiens, has used these abilities to master its natural environment and all other life forms on Earth.
How this came about has been the subject of many theories since Charles Darwin first established the highly corroborated theory that humans are evolved from non-human hominids, and that intelligence, rather than being bestowed on humans by divine providence, must therefore have evolved through a process of natural selection, like any other animal attribute.
As nearly a century of archaeological research has shown, the hominids evolved from earlier primates in eastern Africa. Humans primate ancestors, small mammals resembling lemurs, lived in trees, in the vast tropical forest which then covered all of Africa. Like some non-primate tree-dwelling mammals, such as opossums, they evolved an opposable thumb, which enabled them to grasp tree-branches and creepers as they swung from tree to tree (a method of locomotion called brachiation). The opposable thumb also enabled primates to grasp and manipulate objects, such as fruit: in other words they possessed a true hand, something no other order of mammals possesses. They also possessed front-facing binocular vision.
Around 10 million years ago the earth's climate entered a cooler and drier phase, which led eventually to the ice ages. 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). This forced tree-dwelling animals to adapt to their new environment or die out. 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.
Some primates adapted to this challenge by adopting bipedalism: walking on their hind legs. This gave their eyes greater elevation and the ability to see approaching danger further off. 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 the ability to pick up sticks, bones and stones and use them as weapons, or as tools for tasks such as killing smaller animals or cutting up carcases. In other words, these primates developed the use of technology, an adaptation no other animals have attained. Bipedal tool-using primates became hominids, of which the earliest species, such as Sahelanthropus tchadensis, are dated to about 7 million years ago.
[edit] Development of the brain
Up to this point the hominid brain was no larger or more sophisticated than the brains of other mammals of comparable size. But from about 5 million years ago, the hominid brain began to develop rapidly (in evolutionary terms) in both size and differentiation of function. This was because an evolutionary loop had been established between the hominid hand and brain. The use of tools conferred a crucial evolutionary advantage on those hominids which had this skill - in other words, they were more likely than other species to survive long enough to breed, and thus gradually drove out those species which did not use tools. The use of tools required a larger and more sophisticated brain to co-ordinate the fine hand movements required for this task. Larger-brained species therefore survived and prospered while others did not, and brains got steadily larger. By 2 million years ago Homo habilis had appeared in east Africa: the first hominid to make tools rather than merely use them.
The evolution of a larger brain created a problem for the hominids, 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: still a necessary skill in the dangerous world of 2 million years ago. The solution to this was to give birth at an early stage of foetal development, before the skull grew too large to pass through the birth canal. This is why hominid babies, and especially human babies, are so helpless compared with the babies of other mammals.
This adaptation enabled the hominid brain to continue to grow, but it imposed a new discipline on the hominids. The need to care for helpless infants for long periods of time forced hominids to become less mobile. Hominid bands increasingly stayed in one place for long periods, so that females could care for infants, while males hunted food and fought with other homind bands that competed for food sources. As a result, hominids became even more dependent on tool-making to compete with other animals and each other, and relied less on size and strength. Each successive hominid species had a larger brain relative to its body, and was more gracile (fine-boned) and less physically powerful, than its predecessor.
[edit] Homo erectus, Homo sapiens, and Neanderthal man
These hominids develop language, and the range of non-functional activities we call culture, including art and religion. Homo sapiens, like homo erectus, is a migratory animal. He reached Australia 70,000 years ago, Europe 40,000 years ago (the later date is explained by the Ice Age, which made Europe unsuitable for settlement until the ice retreated), and the Americas 30,000 years ago. Homo sapiens is also an aggressive animal. In the course of his expansion, earlier hominids were exterminated or were out competed for resources. As Colin McEvedy wrote: "If the evidence for man's descent is scanty, we can thank our ancestors, who probably ate most of it."
About 200,000 years ago Europe and the Near East were colonised by hominids known to us as Neanderthal man. Once thought to be a race of homo sapiens, the Neanderthals are now thought to have been a closely related but distinct species. They were larger and stronger than modern humans, and their brains were advanced enough for them to have language and culture. They decorated their tools for aesthetic pleasure and buried their dead in way which suggest spiritual beliefs. Despite these modern characteristics, the Neanderthals were no match for the more numerous homo sapiens when he entered the region about 40,000 years ago, and by 25,000 years ago they were extinct.
[edit] Human culture and civilization
Between 120,000 to 165,000 years ago Homo sapiens had reached his modern physical form in Africa, and was already the unchallenged master of the physical environment, able to hunt and kill any other terrestrial animal and (almost) immune to predators. This dominance allowed a rapid rise in population, which soon reached a point where in some places the human population could no longer be fed by hunting and food gathering. In the fertile river valleys of the Nile, the Euphrates, the Indus and the great rivers of China, this problem was solved by agriculture, which first appeared about 10,000 years ago. The accumulation of food surpluses permitted by agriculture led to the beginnings of urban life and the establishment of the first state, in Egypt in about 2750 BC.
[edit] Discussion
It may be asked whether earlier hominids possessed consciousness as it is experienced and understood by modern humans. Consciousness is an even harder term to define than intelligence. Consciousness is often understood as a quality of the mind comprising subjectivity, self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and one's environment. Thus defined, consciousness can be seen as a by-product of the increasing size and sophistication of the brain, a process driven by the demands of natural selection. The ability to think of oneself as distinct from other humans, to recall the past and speculate about the future, to wonder about things which are not known or which cannot be directly experienced, must all have evolved over the course of hominid history as the brain became larger and its ability to think abstractly more advanced.
In conclusion, the evolution of hominid intelligence can be traced over its course for the past 10 million years, and attributed to specific environmental challenges. It is a misunderstanding of evolutionary theory, however, to see this as a necessary process, and an even greater misunderstanding to see it as one directed to a particular outcome. There are primate species which have not evolved any greater degree of intelligence than they had 10 million years ago: this is because their particular environment has not demanded this particular adaptation of them. Intelligence as an adaptation to the challenge of natural selection is no better or worse than any other adaptation, such as the speed of the cheetah or the venomous bite of the cobra. It is, however, the only adaptation which has allowed a species to establish complete domination over the rest of the natural world. Whether the human species has yet acquired sufficient intelligence to manage this responsibility is a matter for debate.
