What Make us Singularly Humans?

Silvia Helena Cardoso & Renato M.E. Sabbatini


Since 1860, when Charles Darwin, the English naturalist, proposed his well-known theory of natural selection, we do not doubt that the modern human species,  Homo sapiens sapiens, has evolved in a continuum that relates to a primate, which, in a distant past, constituted the "lost link" between the anthropoid primates (a word which means "resembling humans") and the first hominid ("the human genre"). Throughout the 20th century, several paleoanthropological discoveries demonstrated the existence of many species of hominids, such as Australopithecus, all of them originated in Africa, in a period spanning the last 5.5 million years. The gradual development of cranial capacity and brain volume, the appearance of permanent upright position, the invention of tools, symbolic culture, the control of technologies such as fire and the building of shelters, hunting and so on become evident due to the archeological remains of hominids, until the appearance 2 million years ago of  Homo habilis ("handy human")  and Homo erectus ("standing human"), the first species the we may consider as "human" in the modern sense, since they developed complex spoken language, manufacturing of tools, clothes, fire, cooking and so on. Skull capacity increased from 500 to 1,200 cm3 between the first  Homo habilis and Homo erectus, just over one million years, although the facial appearance remained that of an anthropoid. It was the first human species to acquire a global mobility, having reached  the Middle East, China and Java. Its successors, Homo sapiens neandertalensis, that appeared some 300,000 years ago, and Homo sapiens sapiens, that appeared some 120,000 years, increased the cranial capacity to the present value (1,350 cm3), conquered all the regions of the Earth, no matter how distant or inhospitable, developed symbolic representation such as pictoric art, sculpture and music, corporal paintings, weaponry, medicine, domestication of animals, agriculture, spiritual beliefs such as religions, the cult to the invisible, funereal rites and magical superstitions. All these  characteristics and "inventions" were solely cultural and transmitted from generation to generation by means of learning and they are unique among animal species, including other primates.

It is not too difficult to arrive at the conclusion that indeed we are biologically very similar to our "cousins", the great apes (gorillas, chimpanzees and orangutans). In Darwin's time, one of the events that greatly influenced the acceptance of his theory, was the exhibition, by the first time ever, of live gorillas at the London Zoo.  The many things we have in common with them shook the deep conviction of  contemporary Victorians who held that human beings had been created by God as an species altogether different from all others.   For instance, we inherited from the apes' family some fundamental characteristics such as color vision, frontal eyes, planar face, the great development of the neocortex and high manual dexterity, the latter incomparable with any other mammal. From a behavior point of view, all anthropoids are capable of manipulating symbols, and they demonstrate enormous capacity of adaptation to environment by learning. They are capable of using tools fo ra variety of tasks , they use the telesenses (vision and hearing) to interact with the environment , they posses some degree of cultural transmission of knowledge, they present a well-structured social life based on the tribe, sexual and reproductive behavior and complex forms of intra-specific intercommunication. Genetically, we also are very alike: molecular biology determines, for instance that 98 percent of the chimpanzee's genome is identical to ours. In short, we are the so-called "naked apes", to follow the same title of a very successful book by English biologist Desmond Morris. In comparison to other higher mammals we are extremely unprotected. We do not have claws or fangs, our skin is not thick, and we have few hairs. We have handicap to run, jump and swim.

So, how this amazingly fragile animal has managed to take over the whole planet, surviving even the most extremely harsh conditions and has been able to conquer all kinds of environment, even the outer space?  What makes us different from other living creatures? What make us so singularly humans? This has been an anguishing quest since Darwin "took away" our status of dominant species of in the universe...

In fact, humankind possesses several attributes that distinguish it from other species. The upright position, walking with the lower limbs, allowed that higher limbs became free to other functions: the prehensile hand act as a tool, allowing the development of technology; the development of speech and language allowed more adaptable forms of communication; the enlargement of the brain in relation to the size of the body; the development of social and cultural interactions: childhood and youth that last longer, so allowing the basis of a social and cultural interactions as well as the division of tasks in society, control over sex and aggression, etc. Finally, human beings express themselves as individuals. The characteristics involved in this include emotion, motivation and artistic and spiritual expression.

All these characteristic, directly or indirectly, are related to the development of our brain. Thus, we can say that our uniqueness lies in our brain. The enormous brain developed, especially in the brain cortex area, has endowed us with properties that do not exist or exist only in a primitive form in other anthropoids. It is by means of this huge cortex that we possess high levels of synthetic analysis. It is there that our worldview is analyzed, planned and programmed to carry out actions and thoughts.

The large development of the brain, therefore, lead to the birth of what the American cognitive scholars calls the "symbolic species". We develop, by means of lingual symbols, symbolic names for the objects perceived from reality (e.g., "tree"), as well as for abstract concepts (e.g., "love"). Besides the verbal capacity of the brain, we developed the capacity of emitting sounds of high precision, that, manipulated by the symbolic brain, enabled for the first time in the animal scale the extragenic evolution: cultural evolution, or the transmission of knowledge from one human being to another. Thanks to this knowledge thinking and consciousness were developed, which constitutes a unique property of human being (which certainly could exist in other non-human primate, but which nonetheless differ hugely from the human species).

On the other hand, the symbolic capacity of the brain generated remarkable things, such as the genetically determined ability to learn any language or even to create a new one, such as Esperanto, computer languages, etc. It generated also the special ability to invent and to appreciate melodies, harmonic sound, dance, i.e., all those symbolic elements that probably make use of the same brain structures which responsible for speech, for the control and mastery of movements and their overall integration.

Among our unique cultural characteristics, art is probably the noblest human invention. Imagine, for instance, what is required in terms of recruiting billions of neurons, millions of muscle fibers, a huge sensorial, visual and aural capacity, the amazing capacity of memory involved in learning by heart and perform in the piano a Chopin's serenade. For this task, there are billions and billions of neurons trained by long years of practice, spread in all regions of the brain and yet working together in harmony to produce a result of unimaginable complexity.

When man became a tribal animal, at the time it begun walking upright, some 4 million years ago, it became also a hunter and tribal warrior, where social cooperation was an important factor for survival. For sure, all social instincts in human beings were developed well before any intellectual capabilities: maternal instinct, cooperation, curiosity, creativity, compassion, altruism, competitiveness, and so on, are very ancient, and can be observed in some degree in anthropoids, too. Again, human beings distinguish themselves thanks to a strong mental characteristic: we gradually developed self-control, that is, the capacity to modify any social behavior, even an instinctive one, in order to make it more useful to our survival. The more disciplined we are, the more capable of self-control and of planning, the more our rational mind will be able to dominate the emotional and instinctive minds, the more humans we will be.

Therefore, human species also has the singular capacity of controlling the emotional brain by means of the rational brain. This, coupled with the ability to plan, engendered an animal capable of winning through intelligence. All the limits and physical weakness were supplanted, and we became the dominating species, destroying those who opposed us, or using for its own sake other animals, such as the beast of burden, laboratory guinea pigs, or even for food.

What does the future reserve for us? How the human species will be in an environment that we have learned to shape and reconstruct?

It is too early for an answer. We need, no doubt, to understand ourselves better. There are motives to doubt that in the next 50 years we would be able to grasp the inner workings of higher intellectual functions, due to the enormous complexity of the nervous system, for which there are still no adequate study methods. Many philosophers even doubt the possibility of one day the brain understanding itself. Maybe the structural and functional complexity of our brain is so huge that we may never be able to grasp it: it would require a more developed brain to achieve it!  It is possible that our intellect has not been built to understand atoms or to understand itself, but rather to promote the existence of human genes. A person who ponders about this knows that somehow, life is incomprehensible. Eventually, we might understand the complexity of a toad's brain but never our own...

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Illustration: reconstruction of the skull of Homo habilis, the first human being.

The Editors
Silvia Helena Cardoso, PhD. Psychobiologist, master and doctor in Sciences, Founder and editor-in-chief, Brain and Mind Magazine, State University of Campinas. 
Renato M.E. Sabbatini, PhD. Doctor in Sciences (Neurophysiology) by the State University of São Paulo Associate Director of the Center for Biomedical Informatics of the State University of Campinas, Brazil, and president of the Editorial Board, Brain & Mind Magazine. 

Copyright (c) 2000 State University of Campinas, Brazil
An initiative: Center for Biomedical Informatics
Published: 15.Jan.2000