The history of the species shows a general tendency towards the development of a greater intelligence. The evolution of racial intelligence differences in homo sapiens is a continuation of the principles developed here.
1. General principles of the evolution of intelligence
Two principles govern the evolution and increase of intelligence in the animal kingdom.
- The first is that from time to time the species occupy new environments or niches that require a greater cognitive capacity. When this happened, these species adapted by developing larger brains to allow for greater intelligence.
- The second principle is that carnivores and herbivores have embarked on an « arms race » in which carnivores had to become smarter to catch herbivores, while herbivores had to become smarter to avoid capture by carnivores. Richard Dawkins and John Krebs (1979) provided a useful account of this process.
Comparisons between species in terms of brain size and intelligence are problematic because there is a strong association between brain size and body size. The reason is that a large part of the brain is devolved body functions, so that large species have a large brain. To control body size and compare brain size of different species, Jerison devised the concept of encephalization quotient (EQ) as a measure of brain size versus body size. He established the QE of live mammals at 1.0 and expresses the EQs of other extinct and living species against this norm. Jerison defines the intelligence of species as their EQ, which determines the brain’s ability to process information
The evolution of higher EQs as new species have evolved is summarized in Table 15.1 below.
These data were compiled from Jerison (1973, 2000), Richard Cutler (1976), and Paul Harvey and Timothy Clutton-Brock (1985). Rows 1, 2 and 3 in the table show that 225 million years ago, fish and reptiles had an EQ of 0.05 and their EQ had not increased to date.
2. Intelligence of mammals
The intelligence in line 4 of Table 15.1 shows that the EQ of the first mammals that evolved about 225 million years ago was 0.25. It was a fivefold increase in the QE of the reptiles from which they evolved and was the first leap forward in terms of increased EQ and intelligence.
The explanation for this development is that reptiles were largely diurnal and relied primarily on vision to obtain information about the world. As with current reptiles, their behavior consisted largely of cabled responses to visual stimuli. The first mammals were small animals the size of a rat and occupied a nocturnal niche, they slept all day and fed at night. This niche was advantageous because it offered protection against predatory reptiles, but it had the disadvantage of making the vision seriously inadequate for gathering information about the outside world. To overcome this problem, very nocturnal mammals have developed their senses of hearing, smell, touch and an integrating processor to obtain and analyze information from all three senses, as well as vision. They were then able to integrate the information obtained from the four senses to identify predators, food and breeding partners.
The development of information processing capabilities such as hearing, smell and touch necessitated the broadening of auditory, olfactory and tactile brain centers and the development of an integrative capacity to combine information obtained from four senses. These new cognitive functions necessitated a five-fold increase in the encephalization quotient from that of the average fish or reptile from 0.05 to 0.25.
Table 5 shows that 60 million years ago, average mammalian EQ increased to 0.75, which is three times higher than the first mammal’s 0.25. Line 6 shows that over the next 60 million years, the average EQ for mammals increased again to 1.0. Thus, during the 225 million years since their first appearance, the average EQ for mammals has increased about fourfold. This increase is largely attributable to the « arms race » between carnivores and herbivores, each exerting selection pressure on the other to obtain greater intelligence (and higher EQs to accommodate it).
3. Intelligence of the birds
Line 7 shows the appearance of the first birds about 150 million years ago. The first bird, Archeopteryx, had an EQ of 0.10, twice the size of the reptiles from which it had evolved. This represented the second leap forward in EQ and intelligence. Rows 8 and 9 show that 60 million years ago, bird EQ increased to about 0.75 and then to 1.0 in the next 60 million years. Thus, birds currently living have approximately the same EQ of 1.0 as current mammals.
The increase in EQ of birds is explained by their lives largely in the air. This had the advantage of being away from predators, but the disadvantage is that hatchlings newly hatched in the nests at the top of the trees had to be fed for several weeks until they had grown sufficiently to fly and to unravel alone. To raise their chicks, parents had to build nests, know the location of their nests on spatial maps of their land, make connections between mother and father birds and cooperate to feed their young and defend their nests against predators. These tasks obviously required more intelligence and learning abilities, as well as a higher EQ than that required by reptiles, who do not care about their young.
The greater intelligence of birds and mammals, such as dogs and rabbits, has been shown in various experimental task examinations by Gregory Razran (1971). The increase in EQs of birds over time was likely due in large part to the « arms race » between predators and non-predatory birds, each exerting selection pressure on the other to obtain more intelligence .
4. Intelligence in primages
Line 10 shows the EQ of 0.75 of the first primates that appeared about 60 million years ago as a result of dinosaur extinction. The EQ of early primates was about the same as that of mammals and birds of that time. Rows 11 to 15 give the EQs of the living representatives of the first primates and mammals closely related to primates: shrew (QE 0.85), Bosmans potto (QE 1.1), galago (QE 1.2), gentle lemur (0.7) and Black lemur (Eulemur macaco) (QE 1.6). The average EQ is 1.1, an increase of about 50% over that of the first primates of 60 million years ago. Row 16 shows the QE of 1.0 of the first monkeys that appeared about 30 million years ago. Rows 17 to 22 show the EQs of six typical live monkey species. Their EQs range from 1.3 for Gray Langur to 3.5 for the Brown-headed Capuchin (Cebus Apella). They therefore have higher EQs than the first monkeys 30 million years ago with an EQ of 1.0. Row 23 indicates a QE of 2.0 for the first species of monkeys that appeared about 16 million years ago.
Rows 24 to 28 give the QE of the five species of living great apes. EQs are 2.0 (for Central African gorillas) 2.1, (Siamang of Southeast Asia and Indonesia) 2.4 (Borneo and Sumatran orangutan) 2, 6 (the Central African Emperor) 2.8 (Southeast Asian gibbon larand and Indonesia). Great apes (excluding humans) do not seem to have evolved to a higher EQ than monkeys. The average EQ of the five species of great apes is 2.4, while that of the six monkey species is 2.3. (It is important to note that some of these EQs are derived from rather weak numbers and may not be strictly accurate due to sampling errors.) The rapid evolution of EQs from apes and apes, from 1.0 at 2.4 out of 30 million years of existence, is far superior to that of other mammals and birds during the same period.
This was the third big leap in the evolution of brain size and intelligence. There are two reasons for this rapid increase in EQ.
1. While primitive primates were nocturnal like the mammals they came from (Byrne, 2002), monkeys became diurnal, living during the day and sleeping at night. Daytime species rely heavily on vision to obtain information about the outside world, and in accordance with this principle, visual cerebral centers have increased in size in monkeys, which has increased visual processing capacity.
2. While the first primates were solitary, they then began to live in social groups.
Community living has the advantages of ensuring the exclusive use of a territory and its resources, as well as cooperating to find food, raise young people and defend against predators. The cost is that individuals must acquire complex social skills to live in harmony with other members of the group, who are also competitors for food and breeding partners. The social system of these animals generally consists of groups of about 30 to 80, in which there are dominance hierarchies in which two or three dominant males have more food, a single access to females when they are in the oestrus and the best places to sleep in the trees. To maintain their position, dominant males usually form alliances to deal with the challenges posed by beta males. These non-dominant men belong to the group, but must take care to respect the position of the superior men, who will drive them out if not from the group. Nevertheless, non-dominant men seem to understand that if they exercise sober social skills, the time will come when the dominant men will grow old, become weak and die, and some of them will be able to replace them. To maintain their position in the group while waiting for this eventuality, non-dominant monkeys must exercise restraint and judgment in order to wait until they have a good chance of successfully defying and replacing a dominant man. At the same time, they form alliances with other non-dominant males to maintain their position in the group and enhance their chances of becoming dominant. The acquisition of these social skills requires quick learning. These social skills are now called « social intelligence » and seem to require a relatively large EQ (encephalisation quotient) to understand and manipulate social relationships, to observe, learn and memorize the characteristics of other members of the group and to prevent impulsive actions. . Males with high social intelligence eventually become dominant and are able to reproduce, reinforcing the social intelligence of the species. Robin Dunbar (1992) developed the theory that highly social animals needed higher EQ. In primates the size of the social group is correlated with EQs, suggesting that primates living in larger groups need higher EQs to manage the more complex social relations between their members. Thus, monkeys occupied a new niche as cooperative social species requiring greater intelligence (and higher EQs).
The monkeys display a high level of intelligence compatible with their high EQ. The most studied species is the chimpanzee. In the 1920s, Wolfgang Kohler (1925) demonstrated that, faced with a difficult problem, such as retrieving a banana hanging from the ceiling and out of reach, chimpanzees can understand how to use boxes to build a platform on which they can climb to catch the banana. Jane Goodall (1986) has shown that chimpanzees in the wild are learning to make and use tools for a variety of purposes. They take sticks from which they dispose of the lateral stems, then lick them to make them sticky, insert them into the holes of termite mounds and ant nests and eat the termites or ants that adhere to them. They make scissors to open the honeycombs; they use stones to form holes, use leaves to quench their thirst and clean themselves, they can also pick up pieces of wood and hit predators and intruders on their territory. They also have a vocabulary of about a dozen cries to transmit information, including the presence of predators, the intrusion on their territory of neighboring groups, the location of a food supply, the willingness or lack of willingness to share food, etc. More recently, it has been discovered that orangutans also make and use tools (Fox, Sitompul and Van Schaik, 1999). In laboratory studies, only monkeys can master single-trial learning sets, in which different objects are presented and the correct choice varies from day to day.
5. The intelligence of hominids
The fourth leap forward in EQ and intelligence took place with the evolution of hominids. It is the series of species that finally led to the appearance of Homo sapiens. This began about four million years ago in Central East Africa, in present-day Kenya and Tanzania, with the appearance of Australopithecus. Then come the three successive species of Homo habilis, Homo erectus and finally Homo sapiens. The times of these species and their EQs are shown in rows 29 to 32 of Table 15.1. The first hominids, Australopithecus, are composed of several species. Australopithicus afarensis was the first to appear. It comes from a monkey very similar to the chimpanzee. Over the next two million years, other Australopithecine species evolved, including Australopithicus africanus, Paranthropus robustus and Paranthropus boisei. The reason for the appearance of Australopithecus is that apes are adapted to live in forests, but in Central and Eastern Africa, the climate has become drier, as a result much of the forest has disappeared and has been replaced by meadows with some scrub and some clumps of trees. As a result, the great apes of central and eastern Asia had to adapt to survive in the new open savannah niche. Their three most distinctive adaptations were (1) bipedalism, while great apes move normally by walking on all fours; (2) their thumb is against the fingers; and (3) their EQs have increased. The main adaptive advantages of the vertical posture were that, firstly, it gave them a better vision to see predators at a greater distance, second, it allows to travel long distances to search for food and, third, it frees hands. The freeing of hands and the development of a thumb opposable to the fingers made it possible to use the hands to transport food to the camp, to make stone tools, to seize more effectively stones and pieces of wood and to use them. EQs for hominids increased threefold over the last four million years, from 2.6 to about 7.5 at homo sapiens. This is a very fast rate of increase compared to about 56 million years for the same rate of increase in primates, from 0.75 in early primates to about 60 million from years to 2.6 in the most encephalated monkeys and apes.
The explanation for this increase is that hominids entered a new open savannah niche in which survival was more cognitively demanding. The cognitive requirements of the new niche consisted mainly in finding a variety of different foods and protecting themselves from predators. Successive Australopithecus and hominids continued to live mainly on plants, such as the great apes from which they evolved, but in the open savannah these plants became more varied and dispersed over a larger area. To obtain these foods, they needed spatial maps of a large area, which required a larger brain. The foods they ate can be determined from the wear of their teeth, which shows that they lived mainly on a diet consisting of leaves and fruits and that they also ate tubers, nuts, seeds , grasses and insects (Isaac 1978, Parker and Gibson 1977, Grine and Kay 1988, Stahl 1984). Some of them lived on the shores of Lakes Baringo and Turkana in present-day Kenya. They could pick up shells and break them by hitting them with a pebble that they were able to grasp between the thumbs and the fingers. Hominids supplemented their diet with plants and insects with a certain amount of meat obtained by the occasional death of animals. Baboons and chimpanzees sometimes kill small animals for food, although meat has never become more than a small part of their diet (Strum, 1981). Perhaps the Australopithecus and the laterhominids, Homo habilis, did the same. They were also scavengers on the remains of animals killed by lions, cheetahs and leopards. The sites of Homo habilis contain the bones of large herbivores with carnivorous tooth marks on which have been superimposed stone marks carved by hominids. This suggests that large herbivores have been killed by lions, cheetahs and leopards; Then, Homo habilis cleaned the bones, which they broke to extract the marrow and the brains, which the feline predators were incapable of (Binford, (Binford, 1985, Blumenschine, 1989). With its increased EQ of 4.3, Homo habilis became the first hominids with the brain power needed to make large-scale stone tools. By making sharp cutting tools in flint, they made spears and knives to iron the carcasses of large mammals killed by lions, cheetahs and leopards.
In addition to obtaining food, the other main problem of hominids living in open grassland areas has been to protect themselves from feline predators. Monkeys escape danger by climbing trees and swaying or jumping to each other. For Australopithecus and later hominids in open grasslands, this was no longer possible. They had to repel lions, leopards and cheetahs by throwing stones at them and hitting them with sticks made from pieces of wood collected from the few remaining trees. For this, their newly developed thumbs, which have increased their grip, have been a great benefit. Chimpanzees sometimes use sticks to protect themselves from predators, but they do not collect an arsenal of sticks and stones for this purpose. Three additional selection pressures have been proposed to increase the EQs of hominids. First, at one point, inter-group wars developed, during which victorious groups usually killed the men of the vanquished groups and took back their wives and territories. Winning groups tend to have higher IQs than defeated groups, which increases the intelligence of survivors. Second, Richard Alexander (1989) suggested that smarter individuals were more effective as tool makers and hunters, and had increased social intelligence, which allowed them to increase their fertility. Third, Jessica Ash and Gordon Gallup (2007) showed that brain size, from Homo habilis to archaic Homo sapiens, increased in colder and more variable climates away from the equator; they argue that they required greater intelligence to survive in these new conditions. It is also the climate, and especially the main ice age, that is responsible for increasing cranial capacity and intelligence among Europeans and East Asians, compared to breeds that have not been subject to selection of harsh winters. See Evolution of racial differences.
6. IQ monkeys and pre-human hominids
A number of attempts have been made to evaluate the intelligence of monkeys and pre-human hominids using Piaget’s theory of intelligence development in children. Piaget’s theory states that children progress through four stages of cognitive development. The first is the sensorimotor stage of early childhood in which the child learns the properties of objects, space, time and causality. Around the age of two, children move to the « pre-operational » stage, in which they acquire abstract language and concepts but are not yet able to understand logical principles. This stage lasts until the age of about six. In Western societies, children around the age of seven head for the « concrete operations » stage when they can understand logical principles, but only in concrete terms. Around the age of twelve, children enter the fourth and final stage, that of « formal operations, » when they become able to think logically in terms of general principles dissociated from concrete examples. The applications of this theory to the intelligence of apes and pre-humans have been summarized by Parker and McKinney (1999). Their conclusion is that most monkey species do not progress beyond the first stage of Piaget, so they remain at the cognitive level of humans for about two years. On the ladder of human intelligence, their IQ would be about twelve (12). The most encephalated monkeys reach the stage of pre-surgery in Piaget, which corresponds to the cognitive level of the average European aged from three to four years. Their IQ is about 22. Wynn (1989) attempted to estimate the cognitive level reached by successive hominid species on the Piaget scale. His conclusion is that Homo habilis, who lived in East Africa about 2.4 million years ago and made simple tools had to reach an early stage of pre-operational abilities, almost identical to that of monkeys. (IQ of 22). Homo erectus, which appeared around 1.7 million years ago with a slightly larger brain, was able to create more sophisticated stone tools, including bifaceous hand axes, which required concrete operational thinking such as than that produced by contemporary Europeans aged 7 to 8 years. It can be deduced that their IQ was about 50.
We have traced the evolution of intelligence throughout the animal world and arrived at homo sapiens (summary diagram below).
We will now analyze the evolution of intellectual differences between large populations or races of homo sapiens.
Evolution of the intelligence in the animal kingdom, the 4 big quantitative jumps (click to enlarge).