The high cost of being very smart

The development of a large brain could have been paid for with a decrease in physical strength.

The intelligence that characterizes our species has allowed us to perform incredible feats never before seen in the animal world: building civilizations, using language, creating vast social networks, having consciousness and even being able to (almost) read minds.

However, there are reasons to think that the fact of having a privileged brain has cost us dearly..

The price of a big brain

From the point of view of biology, intelligence comes at a price. And it is, moreover, a price that in certain situations could be very expensive. The use of technology and the use of knowledge handed down by past generations may have made us forget this, and yet, since Darwin included us in the evolutionary tree and as science unravels the relationship between the brain and our behavior, the boundary that separates us from the rest of the animals has been crumbling. Through its rubble, a new problem can be glimpsed.

Homo sapiens, as life forms subject to natural selection, have characteristics that can be useful, useless or detrimental depending on the context. Isn't intelligence, our main trait as human beings, just another characteristic? Is it possible that language, memory, the ability to plan... are just strategies that have developed in our organism as a result of natural selection?

The answer to both questions is "yes". Increased intelligence is based on drastic anatomical changesOur cognitive capacity is not a gift bestowed by the spirits, but is explained, at least in part, by drastic changes at the neuroanatomical level compared to our ancestors.

This idea, which was so hard 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 every way, can sometimes be a liability.

Of course, one could argue long and hard about whether the cognitive advances available to us have caused more fortune or more pain. But, to put it simply and immediately, the main drawback of having a brain like ours is, in biological terms, its very high energy consumption.

Energy consumption in the encephalon

Throughout the last millions of years, the evolutionary line that goes from the extinction of our last common ancestor with the chimpanzees to the appearance of our species has been characterized, among other things, by seeing how the brain of our ancestors became larger and larger. With the appearance of the genus Homo, a little more than 2 million years ago, the size of the brain in proportion to the body rose sharply, and since then this set of organs has been enlarging over the millennia.

The result was that inside our head the number of neurons, glia and encephalic structures that were "liberated" from having to dedicate themselves to such routine tasks as muscle control or the maintenance of vital signs increased greatly. This allowed them to process information already processed by other groups of neurons, so that for the first time primate thought had sufficient "layers" of complexity to allow the emergence of abstract ideas. sufficient "layers" of complexity to allow the emergence of abstract ideas, the use of language, the creation of long-term strategies, and the creation of long-term strategies.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 modifications in our nervous system; the existence of intelligent behavior, since it depends on the material basis provided by the tangle of neurons inside our heads, requires that this part of our organism be healthy and well maintained.

In order to maintain a functional brain, we need resources, i.e. energy... and it turns out that the brain is an energetically very expensive organ: Although it accounts for about 2% of the body's total weight, it consumes about 20% of the energy used at rest. used in the resting 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, about 8% of the energy during rest. The energy factor is one of the main drawbacks related to the brain expansion necessary to reach an intelligence similar to ours.

Who paid for brain expansion?

The energy needed to develop and maintain these new brains had to come from somewhere. The difficult part is to know what changes in our body served to pay for this brain expansion.

Until recently, one of the explanations for what this compensation process consisted of was that of Leslie Aiello and Peter Wheeler.

The expensive tissue hypothesis

According to the "expensive tissue" hypothesis of Aiello and WheelerThe increased energy demand produced by a larger brain had to be compensated also by a shortening of the Gastrointestinal tract, another energetically expensive part of our organism. Both the brain and the gut competed during an evolutionary period for insufficient resources, so one had to grow at the expense of the other.

To maintain a more complex brain machinery, our bipedal ancestors could not rely on the few vegetarian morsels available on the savannah; rather, they needed a diet that included a significant amount of meat, a food very rich in protein. At the same time, the digestive system was shortened, with the consequent saving of energy.and consequent energy savings. Moreover, it is quite possible that the habit of hunting regularly was both a cause and a consequence of an improvement in general intelligence and the management of its corresponding energy consumption.

In short, according to this hypothesis, the appearance in nature of a brain like ours would be an example of a clear trade-off: the gain of one quality entails the loss of at least one other quality. Natural selection is not impressed by the appearance of a brain like ours. Its reaction is rather: "so you have chosen to play the intelligence card... well, let's see how you do from now on".

However, Aiello and Wheeler's hypothesis has lost its popularity over the years, because the data on which it was based were unreliable.. It is now considered that there is little evidence that the increase in brain size was as clearly compensated for by a reduction in the size of certain organs and that much of the loss of available energy was cushioned by the development of bipedalism. However, this change alone did not necessarily fully compensate for the sacrifice of resources required to maintain a costly brain.

For some researchers, a portion of the cuts that were made for this is embodied in the diminished 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 weakest of these apes would be able to grab the average Homo sapiens by the ankle and mop the floor with him.

This is a fact referred to, for example, in the documentary Project Nim, which explains the story of a group of people who tried to raise a chimpanzee as if it were a human baby; in addition to the difficulties in educating the ape, there was the danger of its 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 is due to the development that our brains have undergone in the course of their 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 found that the metabolites used in various areas of our brain (i.e., 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. On the other hand, in the same research it was observed that, eliminating the factor of the difference in size between species, ours has half the strength of that of the rest of the non-extinct apes that were studied.

Higher brain energy consumption