When did we humans become intelligent, how did our intelligence appear, what made it emerge, did it emerge gradually from the potentialities of the subject, as Darwin suggested, or was it an act of divine creation, as Wallace claimed? This old discussion is still relevant today.

Scavenging and intelligence

The discussion question of how human intelligence originated, far from being resolved, continues to be a source of controversy today. From the late 1980s onwards, but especially in the 1990s, a naturalistic emergentist explanation began to take shape, in which some scientists suggested that a change in the hominid per diem expenses , introducing relatively abundant meat consumption, would have given rise to larger brains in which intelligence could have begun to emerge. Prominent among these scientists are Leslie C. Aiello and Peter Wheeler, who have been drawing attention to this point for years. According to them, individuals with relatively large brains would have the minimum intelligence to be the first to make tools with which to break the shafts of bones in order to access the marrow, where the most energetic nutrients are found. Thus a diet rich in animal fats and protein allowed for a progressive increase in brain volume. And with this increase, a progressive increase in intelligence development .

In Spain, this thesis has reached the field of popular science with the latest book by Juan Luis Arsuaga: Los aborígenes. Food in human evolution. In this work, Arsuaga insists on the idea of the natural emergence of human intelligence from the restructuring and expansion of the brain made possible by the energetic contribution provided by the consumption of meat. The famous co-director of the Atapuerca sites in Burgos describes the finding of carrion as source as: "the fundamental event in our evolution *(1).

The fiction of the accidental finding of a young Australopithecus afarensis serves as the main thread of the first part of the play. By accidentally hitting an antelope's tibia with a stone and breaking it, thus making it possible to feed on the substances inside, this strand of afarensis opened the way to humanisation. The story is based on the assumption that Australopithecus cracked nuts with stones just as chimpanzees do today. Recent studies in this field include those being carried out in the Ivory Coast jungle by a Spanish archaeologist, Julio Mercader. His research focuses on the study of how chimpanzees in that area crack nuts. For this scientist, it is possible that some of the sites from two million years ago were places where the predecessors of the human lineage carried out this activity. The fact that the bone architecture of the hands of Australopithecus does not present any anatomical impediment for this skill makes something like the one Arsuaga narrates very plausible; however, we must not forget that we have no firm evidence to confirm that Australopithecus cracked nuts with stones and much less that they did so with the bones of deceased animals. Such an assertion, although possible, whether we like it or not, is no more than conjecture. Even the data from the Bouri site in Ethiopia that would point to something of this style 3.5 million years ago have yet to be confirmed, and are not free from conflicting interpretations.

Undoubtedly, the incorporation of a significant amount of animal products in the hominid per diem expenses was the first major change in the history of human nutrition. Did Australopithecus eat meat? It is possible that more recent specimens were already scavenging. In fact Pickford and Senut suggest that Orrorin tugenensis, an alleged six-million-year-old hominin, was already doing so. Two and a half million years ago Homo habilisy and Homo rudolfensis are the first hominins known to have consumed animal flesh from scavenging.

The brain is a very expensive organ to maintain as, in an anatomically modern adult male, it requires 20 % of the total body energy expense , at birth the brain consumes up to 60 % of the body's energy. The digestive system, including very long intestines, as is common in herbivores, is also very expensive to maintain in terms of energy consumption. So: a very large brain and a very bulky digestive system do not usually occur simultaneously in the same living creature. The replacement of an almost exclusively vegetable per diem expenses , very rich in cellulose, by one in which meat, rich in protein, played an essential role, allowed the volume of the brain to increase and the length of the intestines to decrease.

Some have wanted to see in this change of orientation in the per diem expenses of hominids the remote cause of the origin of human intelligence. Thus, in an article graduate: La cuna africana del hombre, published by the magazine Conocer (nº 175, August 1997, p. 55), and signed by Monica Salomone, it can be read: "if the first humans had not complemented the semi-vegetarian per diem expenses of their australopithecine cousins, they would never have been able to afford to be intelligent". William R. Leonard is of a similar opinion and in December 2002 he published an article graduate Food for thought. Dietary change was a driving force in human evolution. The literal translation would be something like: Food for thought. Changes in the per diem expenses were a driving force in human evolution. Next February this article will be published in the journal Investigación y Ciencia (Spanish version of the aforementioned journal), but with an apparently more moderate title: Alimento y mente (Food and mind). Juan Luis Arsuaga is also of this opinion. In an interview granted to the newspaper La Vanguardia, he declared: "The food exploitation of carrion allowed a series of morphological changes to take place in hominids, which ended up making us the way we are. Eating carrion made us intelligent! I already have a headline! (exclaimed the journalist). Let's be clear (Arsuaga clarified): eating carrion did not directly produce this leap, but it allowed it to take place. It allowed a greater brain development : the brain was able to grow..., and it grew. Journalist: Clarify it for me. Meat and intelligence: it sounds like a joke! (...) Did meat make us intelligent? Arsuaga: The per diem expenses with carrion allowed some mutant individual with less intestine to survive (and pass on its genes). And it allowed mutants with bigger brains to sustain it (and pass on their genes). And bigger brains allowed for better technology (stones, blades...)*(2), and better technology made it easier to access more meat. Journalist: A wheel. Arsuaga: The wheel of intelligence! * (3) Eating meat was a cultural change that opened the way to eventual morphological changes, which, once verified, allowed other cultural changes" (La Vanguardia; 24-XI-2002). This is the same argument put forward six years ago by Robert Blumenschine when he stated that: "hominids with relatively large brains were able to make stone tools, and to use them to butcher and butcher the remains of large animals; thus, individuals with large brains could eat better, could have more offspring and, therefore, this characteristic was selected as an adaptive advantage"*(4).

There are even those who think that food played such an important role in human evolution as to be the cause of the appearance of oral language. This is precisely what primatologist Richard Byrne argues when he states that: "language appeared in prehistoric times from the sequences of movements developed to prepare food" (La Vanguardia; 16.X.2002); in other words: manipulating food led, according to Byrne, to the appearance of language. And although this scientist denies that language is the basis of thought, everyone agrees with agreement that language and intelligence are closely related.

Returning to Aiello and Wheeler's central thesis in The Aborigines, which states that hominid meat-eating increased brain size, thus facilitating the gradual emergence of intelligence, leads us to ponder a naïve but pertinent question. If this hypothesis is correct... then why have large carnivores, such as tigers and panthers, which have been eating meat for many millions of years, not developed very large brains, let alone intelligence in the strong sense of the word? Moreover, why have large predators such as the lion or the hyena, the carnivores par excellence, seen their bodies, and hence their brains, shrink by a third over the last couple of million years? One possible answer to the latter would be to say that today's species of lions and hyenas are not direct descendants of the former. Perhaps, but the question remains that their brains are not particularly large despite millions of years of eating meat as an almost exclusive element of their per diem expenses, which is not the case in hominids which, let's not forget, are omnivores and therefore meat consumption is only a part of their per diem expenses.

On the other hand, not all scientists agree with agreement that the human brain has done nothing but grow over the last two and a half million years. Robert D. Martin states: "There is increasing evidence that the brains of the components of our own species Homo sapiens were once larger than they are today. All indications are that there has been a steady reduction in human brain size (without a concomitant decrease in body size) over the last 20,000 years or so. Thus, the size of the human brain has experienced a progressive decline during the same period as the most notable advances in human culture" *(5) , concluding that: "the most significant changes in human society have been accompanied by a progressive decline in our brain size" *(6). Martin accompanies these affirmations with concrete data, stating that Mesolithic humans (some ten thousand years ago) had an encephalisation average of 1593 cc. for males and 1502 cc. for females; in contrast, present-day men have an average of 1436 cc. and women 1241.

Can we know scientifically how human intelligence arose?

En primer lugar hay que decir que nos encontramos ante una explicación materialista del origen de la inteligencia humana que apostaría por un emergentismo gradual, algo que científicamente no está demostrado *(7) ; es más, desde un punto de vista estrictamente científico todavía no se ha podido definir de una forma unívoca el concepto de 'inteligencia', algunos científicos incluso creen que esto jamás podrá lograrse, al menos ese es el parecer de William H. Calvin cuando declara que: "Nunca habrá acuerdo universal sobre una definición de la inteligencia, porque es un vocablo abierto, lo mismo que conciencia" *(8) . Por su parte Arsuaga sostiene que: "eso que llamamos <<inteligencia>> es un concepto de difícil definición y muy problemática medida"*(9) . Esta dificultad facilita la confusión, de ahí que algunos científicos sostengan que ciertas especies de animales tienen inteligencia, mientras que otros la restringen exclusivamente al género humano.

As if this were not enough, the argument represents a circular reasoning, something that in logic is not usually well regarded. According to this hypothesis, it is claimed that the consumption of large quantities of meat is possible thanks to the fact of having voluminous brains that make it possible to have the minimum of intelligence to be able to manufacture the tools that make it possible to butcher and dismember the remains of large animals. But it should not be forgotten that the basic budget of this hypothesis is that big brains are obtained after consuming meat. In final: the conclusion of the hypothesis is also the premise from which it starts. In The Chosen Species, Arsuaga had already realised this when he stated that this topic is like the fish that bites its own tail; in effect: "The brain expansion of Homo could only have been possible in exchange for a variation in the per diem expenses, which in turn translates into a reduction in the size of the digestive tract and, correlatively, of the chewing apparatus. Aiello and Wheeler insist that this does not mean that the change in per diem expenses automatically produced an increase in brain size; they only insist that it was necessary for us to become carnivorous in order to be intelligent (although this is a biting fish in a barrel because high-quality food requires greater mental capacities to be located)". *(10).

We are free to speculate and guess all we want, but we must be aware that we must distinguish between what is a hypothetical evolutionary scenario and what is firmly established scientific truth, and the fact is that science cannot determine with empiriometric accuracy how human intelligence arose.

On the other hand, if human intelligence had been educated by the gradual emergence of the potentialities of the subject, then it would be possible that animals also have intelligence in a lower degree. This is precisely Arsuaga's opinion, when he states that: "human beings are characterised by possessing a much more developed intelligence than the rest of the animals" *(11). Thus, on this point, Arsuaga agrees with Darwin, who was of the opinion that animals also have intelligence, the difference between their intelligence and that of humans being a question of Degree, but not of essence. Strictly speaking, this is not the case, since animals do not have intelligence, as they are not capable of elaborating concepts. What they do have is sensory knowledge . So, with Schools such as imagination, report and others, proper to sensory cognition, they are capable of elaborating "percepts"; that is, they have perceptions that allow them to have an adequate vision of their environment, enabling them to survive; without forgetting the importance that genetic inheritance has in animals in everything that is related to adaptation to the environment. The intellectual knowledge , the elaboration of abstract and universal concepts, is unique to humans. An animal can perceive (and eat) two pieces of meat; but only a human knows what the number two, duality, is. In fact Arsuaga, in The Neanderthal's Necklace, alludes to this topic when he states that: "Jerry Fodor, an influential contemporary psychologist, proposes a division of the mind into perception and cognition. Perception is obtained through a series of modules, independent of each other and innate.... Cognition, on the other hand, is produced in a central system that performs the mental operations we commonly call thinking. This central system is inaccessible to research and remains mysterious". (12) Why doesn't Arsuaga delve deeper into this path? The answer is given in another of his works, specifically in The Chosen Species, when he states that: "the aim of science is to explain natural phenomena (...) by means of natural causes" *(13). (13) The position is entirely permissible; and, in fact, this is what has allowed science to progress as spectacularly as it has in the last four centuries. What is no longer so permissible is to claim that since my way of knowing is based exclusively on a cognition of empirical causality, there is no subject meta-empirical causality. Immanuel Kant criticised this way of arguing with elegance and finesse, not without harshness, when he asked: "Who can prove the non-existence of a cause by means of experience, when experience teaches us nothing else but that we do not perceive a cause? *(14).

The brain as an organ of understanding

It is now almost a cultural a priori of science to consider, without further critical analysis, the brain as the organ of understanding. Thus, from statements such as: "the higher functions related to intelligence are carried out in the brain" *(15) or that: "the part of the brain that is responsible for what we call intelligence is the brain" *(16), it can be inferred that the brain is considered to be the organ of intelligence, of understanding to be more precise, since intelligence is nothing but the act of this power.

Despite how widespread this idea may be, it is not shared by all scientists, and the award Nobel Prize winner in medicine Sir John Eccles disagrees with this view and maintains that intelligence is an immaterial School exclusive to human beings. In fact, Arsuaga himself acknowledges that: "the mind has no seat in any specific region of the brain (...) The mind does not correspond to any material structure"*(17). But... But isn't intelligence something that is part of the human mind?

The topic is not unimportant, for if the brain is the organ of understanding, then the human soul can be neither spiritual nor immortal, but would be a substantial form that would be exhausted in communicating being to the subject and, as happens to all substantial forms of this subject, would be annihilated (or what is the same: nihilised, in the sense of falling into nothingness), with the disappearance of the concrete individual it informs. If this were the case with the human soul, the existence of religion would be meaningless, for there would be no way to have an enduring relationship with God. If the understanding, on the other hand, were a School or power of the soul that did not need the subject as an organ, but as an object in order to elaborate concepts, then the human soul could be spiritual and immortal, and man's openness to transcendence would be founded.

Darwin or Wallace?

What is the origin of human intelligence? In the field of evolutionary scientists, from the beginning there were two positions, that of Darwin and that of Wallace. Arsuaga describes this dichotomy in the following terms: "For Darwin, the evolution of the human mind did not differ substantially from the evolution of the body. It was, therefore, a slow and continuous process, an advance based on small steps and a long time ahead to cover the long evolutionary road that separates the ape from man.... Wallace, on the other hand, simply could not admit that man's lofty intellectual and moral Schools were a product of gradual evolution, and that we had become human beings little by little: he saw a single great qualitative leap, which could not be explained by a slow accumulation of multiple small changes. Wallace thought of a supernatural cause". Following the *(18) of Ian Tattersall, the co-director of Atapuerca, he considers that human intelligence may have arisen by a never-before-experienced readjustment of the elements of the brain, giving rise to an absolutely revolutionary and radically different property: intelligence, an emergent property. And this "is science and not magic, but it is very much like a miracle" *(19) , the truth is that it is. However, although he admits to being a supporter of emergentist materialism, he recognises that there are not many options, so that: "I am afraid (that) we will be forced to choose between Darwin and Wallace" *(20).

Supernatural or natural origin of human intelligence? Divine creation or emergence from the subject? Wallace or Darwin? Although Arsuaga favours Darwin, and his work The Enigma of the Sphinx is a good testimony of this, he recognises with great honesty that it is a topic that, from a scientific point of view, may never be conclusively settled, and that is that: "the question of whether the human mind arose suddenly with Homo sapiens, or whether it is the product of gradual evolution, is an old discussion that has already pitted Darwin and Wallace against each other, and for which it is not known whether an answer will ever be reached final " *(21). What we must not forget is that the scientific knowledge is not the only objectively valid form of knowledge that we humans have. Although positivism as such has lost its force as an official philosophical doctrine, its ballast still makes its effects felt; so that it can be affirmed that the old scientistic spirit of nineteenth-century positivism is still present in the field of science, hence statements like this can still be heard: "science (....) only elaborates hypotheses, hesitant approximations to the truth (...), but it is the best that the human spirit is capable of creating" *(22). Best? In what sense? In absolute or relative terms? We fully agree with agreement that science is the best product that the human spirit can create to solve the scientific problems posed by reality. But, of course, science is not the best thing that the spirit can create to solve the metaphysical questions that challenge man. The epistemological thesis that postulates the scientific knowledge as the supreme form of objectively valid knowledge can only be true if we accompany it with the postulation of another thesis, this time of an ontological character, which maintains that the only existing reality is of subject material. But both theses are no longer scientific but philosophical assertions, so the elucidation of the veracity of their assertions will not be determined by scientific but by philosophical reasoning.

Questions about the origin of man inevitably involve a series of unavoidable ideological debates. And, of course, the same is true of the origin of human intelligence, one of the most important questions for human beings. agreement We fully agree with Arsuaga when he states that: "From the so-called scientific revolution of the Baroque (in the 17th century), science set out to eliminate all emotion and all ideology (religious or political) from its work, with the aim of reaching knowledge goal . Despite this good intention, scientists are human beings and we are conditioned by our environment and our education. We do our best not to be influenced by our surroundings, but we have to recognise that it is easier to do objective science by studying the atom, butterflies or volcanoes than by tackling the thorny question of the human condition" *(23). Precisely for this reason we believe that this effort at objectivity, this seriousness and honesty that must place scientific research above subjective ideological desires is more necessary today than ever, so much so that we believe that the great social prestige that science has attained must necessarily imply greater responsibility on the part of scientists when it comes to making it clear what is certain knowledge and what hypotheses are more or less plausible.

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Notes

1. Juan Luis Arsuaga: The Aborigines. La alimentación en la evolución humana; RBA Libros, Barcelona, 2002, p. 52.
2. In his latest publication, Arsuaga sets out this idea on pages 87-88.
3. In The Aborigines Arsuaga expresses this same idea in the following terms: "The habit of eating carrion created new selection pressures that have led evolution directly to us. That is to say, for once, at least, in the history of life, someone did something that was of enormous significance, because the wheel that it set in motion later produced reason" (op. cit., p. 53).
4. R. Blumenschine: The African Cradle of Man; Conocer Magazine, No. 175, August 1997, p. 55.
5. Robert. D. Martin: Brain Capacity and Human Evolution; in The Origins of Humanity, Research and Science, Issues 19, first quarter 2000, p. 61.
6. Ibid.
7. In fact, Arsuaga describes this theory as "respectable" (Los aborígenes; p. 16), but not absolutely true; and, as he points out elsewhere, "whoever wants absolute truths, unquestionable and immovable dogmas, must look elsewhere, which is not science" (El collar del neandertal. In search of the first thinkers; Ed. Temas de Hoy, Madrid, 1999; p. 40).
8.  W. H. Calvin: The emergence of intelligence; Research and Science; n 219, December 1994, p. 79.
9. J. L. Arsuaga and Ignacio Martínez: La especie elegida. La larga marcha de la evolución humana; Ed. Temas de Hoy, Madrid, 1999, p. 151.
10.  J. L. Arsuaga and I. Martínez; op. cit., p. 185.
11. Ibidem; p. 151. Italics added.
12. J. L. Arsuaga: The Neanderthal Necklace; p. 240.
13. The chosen species; p. 31.
14.  I. Kant: Fundamentación de la metafísica de las costumbres; Ed. Aguilar, Buenos Aires, 1973, p. 98.
15.  The Chosen Species, p. 151.
16.  Ibidem; p. 160.
17. The Neanderthal's Necklace; op. cit., p. 240.
18. The Neanderthal's Necklace; pp. 246-247.
19. Ibidem, p. 247.
20. Ibidem, p. 250.
21.  J. L. Arsuaga: El enigma de la esfinge; place & Janés Editores; Barcelona, 2001, p. 312.
22.  J. L. Arsuaga: The Neanderthal Necklace; p. 40.
23. J. L. Arsuaga: The Aborigines, pp. 129-130.