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The purpose of this article is to reconcile the hypotheses that: (1) brain evolution occurred due to a change in diet, and (2) it occurred due to pressures related to understanding more and more about the underlying causes, such as understanding increasingly complex manipulative and cooperative intentions on the part of the other, as well as understanding reality itself (and how to interact with it beyond group issues). I argue that the ingestion of fat, a highly energy-efficient food, would have unlocked the evolutionary process that culminated in the emergence of the practice of reasoning about underlying causes; and that the consolidation of such a practice resulted in a continuous pressure to increase cognition about “whys”; so that many explanations ended up imposing the need for additional ones, and with that came a high level of awareness and the need for the brain to evolve not only in terms of providing a higher level of cognition but also in size.

The ingestion of fat in the human diet unlocked the evolutionary process that led to rational thinking and a higher level of cognition.


Reality is permeated by patterns of organization, many of which, if identified by an organism so that it can manifest in advance an adequate response pattern to what reality (response pattern that somehow also needs to be identified), allows a substantial increase in the chances of survival in the face of the challenges that reality imposes (see Bates, 2005; Winter, 1998). That said, we can conceive that the evolution of cognitive structures and processes arises from competition for information. However, such evolution can be impeded by limiting mechanisms, such as metabolic and energy costs of the brain (Foley, 1995). In this sense, I see that for an organism to be able, compared to others, to experience a significantly higher rate of cognitive evolution, it must first discover and enjoy a superior source of energy. This seems to have happened with a species of animal, the one that gave rise to humans.   Under the pressure of tremendous food shortages, by accident, a primate lineage appears to have discovered and become adapted to eating food from within the bones of carcasses (e.g., marrow and brain), which contain a highly efficient macronutrient. to generate energy: fat (Thompson et al., 2019). The use of fat as a source of energy would then have enabled the development of a highly effective type of reasoning to increase the organism’s chances of survival: causal reasoning. In this regard, it is important to mention that non-human animals seem to be capable of a rudimentary kind of causal reasoning (Dickinson & Balleine, 2000; Völter & Call, 2017). More specifically, such animals seem to be able to represent, in some way, the invariant sequence of events they detect in reality (e.g., “A” is usually followed by “B”). However, their reasoning seems to stop there. That is, they do not reflect on the unobservable, thus not being able to represent an intangible variable that would possibly be mediating the detected sequence (for example, that “A” is followed by “B” because of “C”) (Penn et al., 2008; Povinelli, 2000, p. 299).   In this sense, I see that in evolutionary time, as the species of animals that gave rise to humans came into contact with reinforcing consequences arising from the cognitive effort to extract underlying causes and act on the basis of such extractions, interest in the “whys” was being established in its nature to the point of becoming consolidated. With that, there would be the consolidation of the tendency to construct and use heuristics that go back to the whys about everything possible, especially why “I” should seek a certain end and through a certain means1. This, in turn, would have been responsible for the emergence of the level of awareness only seen in humans: the awareness that we act in virtue of achieving ends through means, that is, the awareness that we are agents2. The achievement of this point, or evolutionary stage, would coincide with the emergence of a new way of acting in nature, the “rational” way (see also Boyle, 2012), which we can define as: making an informed decision by analyzing whether or not it is worth pursuing an end and by certain means, which takes place through a weighting of consequences based on our network of theories, which involves: 1) assess whether the achievement of an end tends to generate good consequences; and 2) to assess which means are most suitable for the consequence “achievement of an end”, in case it has been decided that it is really worth trying to achieve it (Osmo, 2021; Osmo, Borri, & Falcão, 2022).    The concomitant consolidation of the interest in the whys (in acquiring wisdom), which would have provided the emergence of agency consciousness, and the interest in acting on the basis of explanations (in acting rationally), would then coincide with the emergence of humans, which we conceive today as being “sapiens” and rational”. In fact, we name the current species as “sapiens”, but the interest in accumulating explanations of reality is probably something that would have already been established in other “homos”. Nevertheless, it is a fact that the brain size of the current “homo” is significantly larger. So we need to contemplate, in this analysis, the reason for this evolution to have occurred.   In my view, there would have been a continuous pressure to increase cognition due to another dimension of reality having opened up with the interest in causal mechanisms; so that many explanations ended up imposing the need for additional explanations. This is the case, for example, when one member of the group develops a successful theory of how to exploit the other; the other needs to build a theory about the explorer’s theory so that he or she can detect the exploitative attempt in time to avoid it3 (see Byrne, 1997). I also see that the pressure to increase cognition in “homo” was accompanied by a gradual elaboration and consolidation of rational heuristics, shortcuts related to how to evaluate something and behave in the face of this something that goes back to the network of explanations that the individual has so far. In material terms, this would be reflected in the gradual emergence and expansion of brain structures responsible for enabling the elaboration of increasingly refined rational heuristics and accommodation of neuronal networks that allow their use whenever reality, in some way, imposes the need (cf. Pinker, 2021, p. 97; Fowers, 2015, pp. 47–48). In this regard, it is worth mentioning that the emergence and expansion of brain structures necessarily imply the growth of its size, since evolution does not occur by discarding old structures to make room for new ones (as when we change a processor from a personal computer for a more efficient one without needing a bigger computer for that) (Pinker, 2001, p. 182); instead, evolution takes place through the use of old structures, from which new ones develop, and this also applies to structures responsible for cognition (Cosmides & Tobby, 1997; Fowers, 2015, pp. 50–52).  Final Considerations  In this article, I argued that it would have been the adoption of a fat-focused diet that would have provided the necessary energy support to make it possible to reason about underlying causes and, therefore, to experience the reinforcing consequences that the reach of explanations of reality, and of the acting on the basis of them, is capable of providing. The ingestion of fat would then have unlocked the evolutionary process that culminated in the emergence of humans. However, I would like to point out that, in my view, it was not the consumption of fat per se that would have led to the growing interest in underlying causes and acting on “whys”, but rather the reinforcing consequences experienced in discovering such causes. In other words, the consumption of fat would have allowed for initially accidental thinking about explanations to occur; and when it happened, this type of thinking ended up being reinforced by advantageous consequences, becoming then, little by little, a consolidated practice. In this process, there would have been a continuous pressure to increase cognition, since another dimension of reality opened up with the interest in underlying causal mechanisms; so many explanations ended up imposing the need for additional explanations, and with that came the need for the brain to evolve not only in terms of providing a higher level of cognition but also in size.


This study has produced a hypothesis that there is a gas pedal behind human intelligence that could be as simple as the ingestion of animal fat over millions of years. This has always been one of my fundamental ideas behind the creation of this website. I just don't think it's fair to credit other explanations as more fundamental than the ingestion of animal fat. 

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