The high cost of being very smart

The intelligence that characterizes our species has allowed us to perform incredible feats never seen before in the world. animal: building civilizations, using language, creating very broad social networks, being aware 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 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 handed down by past generations can make us forget about this, and yet 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 other animals has disappeared collapsing. Through its rubble a new problem is glimpsed.

Homo sapiens, as life forms subject to natural selection, have some characteristics that can be useful, useless or harmful depending on the context.

Isn't intelligence, our main trait as human beings, one more characteristic? Is it possible that language, memory, the ability to plan... Are they just strategies that have 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 ability is not a gift granted by spirits, but 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 every way, can be a drag in some occasions.

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

energy consumption in the brain

Over the past few million years, the evolutionary line 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 getting bigger every time further. With the appearance of the genus Homo, a little over 2 million years ago, this size of the brain in proportion to the body rose sharply, and since then this set of organs has been getting bigger with the passage of time. millennia.

The result was that inside our heads the number of neurons, glia and brain structures that were left increased a lot. "liberated" from having to dedicate themselves to tasks as routine as muscle control or maintaining constant vital. This meant that they could dedicate 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 sufficient complexity to allow the appearance of abstract ideas, the use of language, the creation of long-term strategies, and, ultimately, everything that we associate with the intellectual virtues of our species.

However, the biological evolution it is not something that in itself pays the price of these physical modifications in our nervous system. The existence of intelligent conduct, by depending on the material base offered by this tangle of neurons that are inside our heads, it needs that part of our body to be healthy and well maintained.

In order to maintain a functional brain, resources are needed, that is, energy... and it turns out that the brain is an energetically very expensive organ: Although it accounts for about 2% of the total body weight, it consumes more or less 20% of the energy used in idle state. In other contemporary apes, the size of the brain compared to the rest of the body is lower and, of course, so is its consumption: on average, around 8% of the energy during the repose. 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 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 this expansion of the brain.

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

The expensive fabric hypothesis

According to the "expensive tissue" hypothesis 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 body that is also very expensive energetically. 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 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 very high-protein food. At once, stop relying on plants at mealtimes allowed the digestive system to shorten, with the consequent energy savings. In addition, it is very 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 another quality. Natural selection is not impressed by the appearance of a brain like ours. His reaction is more like: “so you have chosen to play the intelligence card… well, let's see how it goes from now on”.

However, the Aiello and Wheeler hypothesis has lost its popularity over time, because the data on which it was based were unreliable. There is currently considered to be little evidence that brain enlargement paid off with as clear a trade-off as reduction in the size of certain organs and that much of the loss of available energy was cushioned by the development of the bipedalism. However, this change alone did not have to fully compensate for the sacrifice involved in spending resources to maintain an expensive brain.

For some researchers, a portion of the cuts that were made for this is captured in the diminishing strength of our ancestors and ourselves.

the weakest primate

Although an adult chimpanzee rarely exceeds 170cm in height and 80kg, it is well known that no member of our species would be able to win a hand-to-hand fight with these animals. The puniest of these apes would be able to grab the average Homo sapiens by the ankle and mop the floor with it.

This is a fact that is referred to, for example, in the documentary Project Nim, which tells the story of a group of people who tried to raise a chimpanzee as if it were a human baby; The difficulties in educating the ape were compounded by the danger of their outbursts of anger, which could end in serious injuries with alarming ease.

This fact is not accidental, and it has nothing to do with that simplistic vision 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 undergone throughout its biological evolution.

Also, it seems that our brain has had to develop new ways of managing energy. In an investigation 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 (that is, the molecules used by our body to intervene in extracting energy from other substances) have evolved at a much faster rate than have those of other species of primates. 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 they studied.

Increased consumption of brain energy

Since we do not have the same body robustness as the rest of large organisms, this greater consumption at the level of head has to be constantly balanced by clever ways of finding energy resources using all the body.

For this reason, we find ourselves in an evolutionary blind alley: we cannot 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 ability to plan and imagine provided by the very organ that has robbed us of strength.

• You may be interested in: "theories of human intelligence"

Bibliographic references:

• Aello, L. C., Wheeler, P. (1995). The expensive tissue hypothesis: the brain and digestive system in human and primate evolution. Current Anthropology, 36, p. 199 - 221.

• Arsuaga, J. L. and Martinez, I. (1998). The Chosen Species: The Long March of Human Evolution. Madrid: Planet Editions.

• Bozek, K., Wei, Y., Yan, Z., Liu, X., Xiong, J., Sugimoto, M. et al. (2014). Exceptional Evolutionary Divergence of Human Muscle and Brain Metabolomes Parallels Human Cognitive and Physical Uniqueness. Plos Biology, 12(5), e1001871.