The Evolution of Human Intelligence

Renato M.E. Sabbatini, PhD


One of the most fascinating themes of science is how human intelligence arose in the course of evolution of apes to hominids to modern human. It is fascinating because it gives to us the key to a trove of understanding about ourselves, and how natural selection could produce such a marvel as the human brain and its capacities in such a short time. It is also an explanation about the nature of our uniqueness among the animal kingdom, and why we are so today.

In fact, many facets of human evolution of human intelligence are still a matter of considerable mistery, because it cannot be observed directly in the paleontological record, like a bone, or teeth, for instance. The evidence amassed by scientists about it comes indirectly from the observation of the increase in the size of cranial capacity, of artifacts produced as a result of human intelligence, such as the manufacturing of tools and cooperative hunting and war, the use of fire and cooking, art and burial of the deceased, and a few other things.

The appearance of intelligence, alongside with language (and both are inextricably intertwined, as we shall see later on) has been a spectacular step in animal evolution. It appeared in primates, but it could have developed as well in other advanced mammals, such as dolphins. Why it developed in primates and not in other animal genera? Probably because of the inherent instability of terrestrial environments, when compared with aquatic ones, and almost certainly due to a series of dramatic changes in African climate in a certain point of geological history. Thus, chance phenomena might well be the explanation for why we are now in the position of the most intelligent of all animals in Earth.

This evolutionary step has been spectacular because it gave origin to a increasingly fast circle of positive feedback between cultural evolution (brought about by language) and further development of the brain (by increasing enormously the reproductive success and chances of survival of the organisms  thus "armed" with a brain capable of high flexibility, adaptability and capacity for learning). In a period of one to two million years (practically an eyeblink in terms of geological time), this powerful surge of neural evolution led to what we are today, and to what man has been in the last 100,000 years.

Is intelligence unique to humans? Of course not. Human intelligence seems to be composed of a number of correlated and cooperating neural functions, many of them already present in other primates, such as manual dexterity, highly sophisticated and accurate stereoscopic color vision, recognition and use of complex symbols (abstract things that represent others), long-term memory, etc. In fact, the current scientific view is that there are several degrees of complexity of intelligence present in mammals and that we share with them many features that we previously thought were unique to man (such as symbolic language, which has been proved to occur in apes).

Scientist have hypothesized about the existence of a "critical mass" of neurons as the pre-requisite for the evolutionary "explosion" of intelligence. In other words, below a certain number of neurons (or size of the brain), intelligence is highly limited and does not lead to invention, imagination, symbolic social communication and other things that do not exist in non-human brains. A number of converging evolutionary factors determined a sharp increase in the size and complexity of the brain of hominids and led to the first true Homo species. Critical mass was achieved and afterwards it was a matter of quantitative evolution, only.

Defining intelligence

But what is intelligence? Before embarking on a voyage to the understanding of its evolution, we must know better the object of our quest.

It seems that there are as many definitions of intelligence as there are scientists working in the field. According to Encyclopaedia Britannica, it is the "ability to adapt effectively to the environment, either by making a change in oneself or by changing the environment or finding a new one". This is a clever definition, because it embodies learning (a change in oneself), manufacturing and sheltering (changing the environment) and migration (finding a new environment). Intelligence is a multifactorial entity, involving things such as language, thought, memory, imagination, reasoning, conscience (the perception of self), capacity for learning and integration of several sensory modalities. In order to adapt effectively, the brain must use all these functions. Therefore, "intelligence is not a single mental process, but rather a combination of many mental processes directed toward effective adaptation to the environment.", continues EB.

Recognizing what are the components of intelligence is very important in terms of assembling a "theory of intelligence". One of the most solid and interesting ones has been proposed by Sternberg (see box), and directly relates to what we know about its evolution. He proposes that intelligence is made of three integrated and interdependent aspects: the internal world, the relationships to the external world, and experiences which interrelates the internal and external worlds.

The Components of Intelligence
The internal world: cognition
  1. processes for deciding what to do and for deciding how well it was done
  2. processes for doing what one has decided to do
  3. processes for learning how to do
The external world: perception and action
  1. adaptation to existing environments
  2. the shaping of existing environments into new ones,
  3. the selection of new environments when old ones prove unsatisfactory
The integration of the internal and 
external worlds through experience
  1. the ability to cope with new situations
  2. processes for setting up goals and for planning
  3. the shaping of cognitive processes by external experience

One of the best examples which showcase all three aspects of intelligence is cooperative hunting. The external world is characterized by an extensive three-dimensional landscape with either swift or large or dangerous animals as potential preys. Learning how to stalk prey, to approach it and to strike it with a stone axe are cognitive abilities. Being able to hunt in several different environments, to move over other areas when hunting becomes scarce and to manufacture hunting weapons, animal traps, etc., are examples of processes related to the external world. Finally, being able to communicate and to coordinate hunting with other human beings, to set up a strategy for hunting more effectively, and for developing and sustaining the whole process of hunting by means of cognition, perception and action, are examples of the integration between the external and internal worlds.

How much of human intelligence, though, reasoning, imagination and planning is due to language? Almost everything, we could say. In fact, these processes are a kind of "internal language processing", as they may. One of the foremost experts in human evolution, Ian Tattersall, of England, has proposed that humankind's success has been largely the result of language, in all its richness of syntax and semantics. Language, therefore, is fundamental to our ability to think; and the human intellect and achievements we are going to highlight in this article would be impossible without language. To Tattersal, language is "more or less synonymous with symbolic thought," and this make all the difference.

In this context arises one of the most important properties of human mind, which is conscience, or self-awareness. We don't have much evidence whether they exists in other animals, and when or where they appeared in humans for the first time. Is self-awareness a product of evolution? Is it advantageous for adaptation and survival? The answer is yes. Self-awareness permits one to construct a reality beyond the mere physical senses, as in picturing a situation and the consequences of our actions in our heads, before anything happens.


The Author

Prof. Renato M.E. Sabbatini, PhD is a neuroscientist and a specialist in medical informatics, holding a doctoral degree in neurophysiology by the University of São Paulo, Brazil, and a post-doctoral fellowship at the Max Planck Institute for Psychiatry, in Munich, Germany. He is the director of the Center for Biomedical Informatics and associate professor and chairman of medical informatics at the Faculty of Medical Sciences, both at the State University of Campinas, Brazil.
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Copyright (c) 2001 Renato M.E. Sabbatini
State University of Campinas, Brazil
First published on: February 15th, 2001
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