The intelligence that characterizes our species has allowed us to perform incredible feats and never before seen in the animal world: build civilizations, use language, create very broad social networks, be aware and even be able to read the mind.
However, there are reasons to think that having a privileged brain has cost us dearly.
The price of a great brain
From the point of view of biology, intelligence has a price. And it is also a price that in certain situations could be very expensive. The use of technology and the use of knowledge given by past generations can make us forget this and, however, since Darwin included us in the evolutionary tree and as science unravels the relationship between the brain and our behavior, the border that separates us from the rest of animals has been collapsing.
Homo sapiens, as life forms subject to natural selection, we have some characteristics that may be useful, useless or harmful depending on the context. Our main feature as human beings is not intelligence, which one is it? Is it possible that language, memory or the ability to plan are only strategies that have been developed in our body as a result of natural selection?
The answer to both questions is “yes”. Greater intelligence is based on drastic anatomical changes; our cognitive capacity is not a gift granted by the spirits, but it is explained, at least in part, by drastic changes at the neuroanatomical level compared to our ancestors.
This idea, which was so difficult to admit in Darwin’s time, implies that even the use of our brain, a set of organs that seems to us so clearly advantageous in all senses, can be a drag on some occasions.
One could argue at length about whether the cognitive advances available to us have caused more fortune or more pain. But, going to the simple and the immediate, the main drawback of having a brain like ours is, in biological terms, its very high energy consumption.
Energy consumption in the brain
Over the last few million years, the evolutionary line that goes from the extinction of our last common ancestor with chimpanzees to the appearance of our species has been characterized, among other things, by seeing how the brain of our ancestors was going enlarging more and more. With the appearance of the genus Homo, something more than 2 million years ago, this brain size in proportion to the body rose sharply, and since then this set of organs has been enlarged with the passage of millennia.
The result was that inside our head there was a lot of neurons, glia and brain structures that were “freed” from having to dedicate themselves to routine tasks such as controlling muscles or maintaining vital signs. This meant that they could devote themselves to processing the information already processed by other groups of neurons, making for the first time the thought of a primate had the “layers” of complexity enough to allow the appearance of abstract ideas, the use of language, the creation of long-term strategies, and, in short, everything that we associate with the intellectual virtues of our species.
However, biological evolution is not something that in itself costs the price of these physical changes in our nervous system. The existence of intelligent behavior, to depend on the material base offered by that tangle of neurons that are inside our heads , you need that part of our body to be healthy and well maintained.
In order to conserve a functional brain, resources are needed, that is, energy and it turns out that the brain is a very expensive energetic organ: although it accounts for around 2% of the total body weight, it consumes more or less 20% of the energy used in rest state. In other apes contemporary to us, the size of the brain compared to the rest of the body is smaller and, of course, so is its consumption: on average, around 8% of the energy during rest. The energy factor is one of the main drawbacks related to the brain expansion necessary to have an intelligence similar to ours.
Who paid for the expansion of the brain?
The energy needed to develop and maintain these new brains had to come from somewhere. The difficult thing is to know what changes in our body served to pay for that expansion of the brain.
Until recently, one of the explanations about what this compensation process was was that of Leslie Aiello and Peter Wheeler.
The hypothesis of the expensive tissue
According to the hypothesis of the “expensive tissue” of Aiello and Wheeler, the greater energy demand produced by a larger brain had to be compensated also by a shortening of the gastrointestinal tract, another part of our organism that is also very expensive energetically. Both the brain and the intestine competed during an evolutionary period for insufficient resources, so one had to grow to the detriment of the other.
To maintain a more complex brain machinery, our bipedal ancestors could not depend on the few vegetarian bites available in the savanna; they needed a diet that included a significant amount of meat, a very protein-rich food. At the same time, to stop depending on the plants at the time of eating allowed the digestive system to shorten, with the consequent saving of energy. In addition, it is quite possible that the habit of hunting regularly was cause and at the same time consequence of an improvement in the general intelligence and the management of its corresponding energy consumption.
In short, according to this hypothesis, the appearance in the nature of an encephalon like ours would be an example of a clear trade-off: the gain of a quality entails the loss of at least one other quality. Natural selection is not impressed by the appearance of a brain like ours. His reaction is rather: “So you have chosen to play the letter of intelligence … well, let’s see how it goes from now on.”
However, the hypothesis of Aiello and Wheeler has lost its popularity over time, because the data on which it was based were not reliable. Currently, it is considered that there is little evidence that the increase in the brain was paid with compensation as clear as the reduction in the size of certain organs and that much of the loss of available energy was cushioned thanks to the development of bipedalism. However, only this change did not have to completely compensate for the sacrifice involved in using resources to maintain an expensive brain.
For some researchers, a portion of the cuts that were made for it is reflected in the diminution of the strength of our ancestors and ourselves.
The weakest primate
Although an adult chimpanzee rarely exceeds 170 cm in height and 80 kg, it is well known that no member of our species would be able to win a hand-to-hand fight with these animals. The most puny of these apes would be able to grab the middle Homo sapiens by the ankle and scrub the ground with it.
This is a fact referred to, for example, in the documentary Proyecto Nim, in which the story of a group of people who tried to raise a chimpanzee as if it were a human baby is explained; the difficulties in the education of the ape were joined by the dangerousness of their outbursts of anger, which could end in serious injuries with alarming ease.
This fact is not accidental, and has nothing to do with that simplistic view of nature according to which wild beasts are characterized by their strength. It is quite possible that this humiliating difference in the strength of each species is due to the development that our brain has suffered throughout its biological evolution.
In addition, it seems that our brain has had to develop new ways of managing energy. In a research whose results were published a couple of years ago in PLoS ONE, it was proved that the metabolites used in several areas of our brain (that is, the molecules used by our body to intervene in the extraction of energy from other substances) have evolved at a much faster rate than those of other primate species have. On the other hand, in the same investigation it was observed that, eliminating the factor of the difference in size between species, ours is half as strong as that of the other non-extinct apes that were studied.
Greater cerebral energy consumption
As we do not have the same body robustness as other large organisms, this greater consumption at the level of the head has to be constantly compensated by intelligent ways of finding energy resources using the whole body.
We are therefore in an alley with no return of evolution: we can not stop looking for new ways to face the changing challenges of our environment if we do not want to perish. Paradoxically, we depend on the capacity to plan and imagine that it provides us with the same organ that has stolen our strength.