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 seven million years, from the separation of the genus Pan until the emergence of behavioral modernity by 50,000 years ago. The first three million years of this timeline concern Sahelanthropus, the following two million concern Australopithecus and the final two 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 somewhat apparent in other great apes, although they are observed in much less sophisticated forms than what is found in humans.

History

Hominidae

The great apes show some cognitive and empathic abilities. Chimpanzees can make tools and use them to acquire foods and for social displays; they have mildly complex 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. One common characteristic that is present in species of "high degree intelligence" is a brain of enlarged size. Additionally, these species have a more developed neocortex, a folding of the cerebral cortex, and von Economo neurons. Said neurons are linked to social intelligence and the ability to gauge what another is thinking or feeling and are also present in bottlenose dolphins.

Homininae

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. 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 where 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 their 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 from the subtribe Hominina date back to as far as about 5 to 7 million years ago, such as one of the earliest species, Sahelanthropus tchadensis.
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, starting from about 600 cm³ in Homo habilis up to 1500 cm³ in Homo neanderthalensis. Thus, in general there's a positive correlation between brain volume and intelligence. However, modern Homo sapiens have a brain volume slightly smaller than neanderthals, and the Flores hominids, nicknamed hobbits, had a cranial capacity of about 380 cm³ about a third of that of Homo 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.

''Homo''

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 same vicinity as multiple Australopithecus fossils may put to question how much more intelligent than its predecessors H. habilis was.
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 therapeutic use of toothpicks.
A larger brain requires a larger skull, and thus is accompanied by other morphological and biological evolutionary changes. One such change required for the female to have a wider birth canal for the newborn's larger skull to pass through. 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. Other accompanying adaptations were the smaller maxillary and mandibular bones, smaller and weaker facial muscles, and shortening and flattening of the face resulting in modern-human's complex cognitive and linguistic capabilities as well as the ability to create facial expressions and smile. Consequentially, dental issues in modern humans arise from these morphological changes that are exacerbated by a shift from nomadic to sedentary lifestyles.
Humans' increasingly sedentary lifestyle to protect their more vulnerable offspring led them to grow even more dependent on tool-making to compete with other animals and other humans, and rely less on body size and strength.
About 200,000 years ago Europe and the Middle East were colonized by Neanderthals, extinct by 39,000 years ago following the appearance of modern humans in the region from 40,000 to 45,000 years ago.
History of humans
In the Late Pliocene, hominins were set apart from modern great apes and other closely related organisms by the anatomical evolutionary changes resulting in bipedalism, or the ability to walk upright. Characteristics such as a supraorbital torus, or prominent eyebrow ridge, and flat face also makes Homo erectus distinguishable. Their brain size substantially sets them apart from closely related species, such as H. habilis, as seen by an increase in average cranial capacity of 1000 cc. Compared to earlier species, H. erectus developed keels and small crests in the skull showing morphological changes of the skull to support increased brain capacity. It is believed that Homo erectus were, anatomically, modern humans as they are very similar in size, weight, bone structure, and nutritional habits. Over time, however, human intelligence developed in phases that is interrelated with brain physiology, cranial anatomy and morphology, and rapidly changing climate and environments.

Tool-use

The study of the evolution of cognition relies on the archaeological record made up of assemblages of material culture, particularly from the Paleolithic Period, to make inferences about our ancestors' cognition. Paleo-anthropologists from the past half-century have had the tendency of reducing stone tool artifacts to physical products of the metaphysical activity taking place in the brains of hominins. Recently, a new approach called 4E cognition has been developed by cognitive archaeologists Lambros Malafouris, Thomas G. Wynn, and Karenleigh A. Overmann, to move past the "internal" and "external" dichotomy by treating stone tools as objects with agency in both providing insight to hominin cognition and having a role in the development of early hominin cognition. The 4E cognition approach describes cognition as embodied, embedded, enactive, and extended, to understand the interconnected nature between the mind, body, and environment.
There are four major categories of tools created and used throughout human evolution that are associated with the corresponding evolution of the brain and intelligence. Stone tools such as flakes and cores used by Homo habilis for cracking bones to extract marrow, known as the Oldowan culture, make up the oldest major category of tools from about 2.5 and 1.6 million years ago. The development of stone tool technology suggests that our ancestors had the ability to hit cores with precision, taking into account the force and angle of the strike, and the cognitive planning and capacity to envision a desired outcome.
Acheulean culture, associated with Homo erectus, is composed of bifacial, or double-sided, hand-axes, that "requires more planning and skill on the part of the toolmaker; he or she would need to be aware of principles of symmetry". In addition, some sites show evidence that selection of raw materials involved travel, advanced planning, cooperation, and thus communication with other hominins.
The third major category of tool industry marked by its innovation in tool-making technique and use is the Mousterian culture. Compared to previous tool cultures, in which tools were regularly discarded after use, Mousterian tools, associated with Neanderthals, were specialized, built to last, and "formed a true toolkit". The making of these tools, called the Levallois technique, involves a multi-step process which yields several tools. In combination with other data, the formation of this tool culture for hunting large mammals in groups evidences the development of speech for communication and complex planning capabilities.
While previous tool cultures did not show great variation, the tools of early modern Homo sapiens are robust in the amount of artifacts and diversity in utility. There are several styles associated with this category of the Upper Paleolithic, such as blades, boomerangs, atlatls, and archery made from varying materials of stone, bone, teeth, and shell. Beyond use, some tools have been shown to have served as signifiers of status and group membership. The role of tools for social uses signal cognitive advancements such as complex language and abstract relations to things.