Human Intelligence Under Question

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David Rabadà

Since my school days, I have been persistently exposed to the oft-repeated mantra that humans are rational animals. Yet, after travelling through numerous conflict-ridden countries—from Yemen to Myanmar—I have come to realise, with a heavy heart, that such a claim is a colossal deception. If we were indeed as rational as we have been taught to believe, wars and abuses of power would have ceased millennia ago. Studies on human evolution continue to idolise brain expansion as a triumph of our rationality, but the evidence suggests the opposite: humanity is not progressing as it ought. We are more emotional than rational beings.

Climatic changes exert evolutionary pressures, and perhaps this was the cause behind the emergence of new relatives of ours. In 2001, the palaeoanthropologist Lee Berger proposed a hypothesis in his book In the Footsteps of Eve. He suggested that between 3 and 2.5 million years ago, an intensification of global cooling reduced the extent of tropical forests and expanded savannahs. Later findings have confirmed that even before 2.5 million years ago, global cooling events were taking place, largely due to the closing of the Isthmus of Panama. This process culminated around 2.7 million years ago, permanently separating the waters of the Pacific and Atlantic Oceans and restructuring both oceanic and atmospheric circulation in the Northern Hemisphere. This led to increased precipitation at higher latitudes, the cooling of the Arctic Ocean, and the growth of sea ice and glaciers in Greenland. This gradual cooling ultimately gave rise to the alternating warm and cold periods that have characterised the planet’s climate over the past 2.58 million years.

In the African Rift Valley, this process resulted in its greatest aridity around 2.5 million years ago, leading to the replacement of many forest species by savannah dwellers. Today, bonobos, chimpanzees, and gorillas are in decline, along with their forests. At that time, it was certain colobus monkeys, cercopithecines, and australopithecines that declined. Their high degree of specialisation may have prevented them from adapting to the new environmental conditions. The surviving apes, if they were to endure, had two options: either specialise once more or become more generalist. And the latter seems to have occurred. In that context, from among the bipedal and terrestrial apes, two evolutionary paths emerged. One branch became highly specialised, robust, and possessed small brains, while the other evolved into more generalist, gracile forms which eventually exhibited increased brain volume—at least, according to a relatively favourable hypothesis.

The first, specialised trend corresponds to the so-called Paranthropus species, formerly known as Australopithecus robustus and related forms. They developed large jaws with thick enamel suited to an abrasive diet of seeds and roots, although they also consumed insect protein and small mammals. Nevertheless, they retained many characteristics of their Australopithecus ancestors: a bipedal gait, a torso more simian than Homo-like, long arms and short legs, short stature, marked sexual dimorphism, greatly reduced or absent canines, a horseshoe-shaped dental arch, and a very small brain. However, this evolutionary lineage appears to have gone extinct between 2 and 1 million years ago. Many of the fossil remains discovered belong to individuals who were hunted and consumed by leopards. Today, the baboon—their main competitor at the time—occupies their former habitat. We must therefore assume that the baboon outcompeted Paranthropus. Evolution is either a train filled with opportunities or a collision strewn with cadavers.

The second evolutionary path went in the opposite direction. Instead of specialising, these species gained increased adaptability to a variety of ecosystems, both open savannah and forested environments. They likely diversified their diet to include more scavenged meat and bone marrow. This may have allowed them to avoid direct competition with baboons, which, as we recall, replaced the Paranthropus. Moreover, this group of apes seems to have reduced their vulnerability to predation, unlike their Paranthropus relatives. By maintaining a partially arboreal lifestyle and perhaps sleeping in trees, they may have lessened the risk of being preyed upon. Whatever the case, this group survived and appears to have given rise to the first large-brained apes—among them, some of our own ancestors. Thus, encephalisation became a key evolutionary trait. Yet, it came at a cost: birth became more difficult due to the baby’s considerably larger skull compared to that of other extant apes. The infant’s head barely passed through the female’s pelvic canal, making childbirth a complicated affair. It is believed that even the small Australopithecus afarensis, barely over a metre tall, suffered this problem. Nonetheless, the inconvenience must have been outweighed by the benefits, as the reproductive rate of encephalised species increased. In other words, our ancestors improved their chances of persistence. But at this point, one must question the very concept of encephalisation and whether it is not merely an anthropocentric artefact.

The average brain weight of australopithecines, chimpanzees, and gorillas is estimated between 400 and 600 grams. Ours, in contrast, averages more than double that—around 1,300 grams. But compared with the 5,700 grams of an elephant’s brain, we fall short of the maximum. That is, absolute brain size alone is not a reliable measure of encephalisation among mammals. Another approach is the Encephalisation Quotient (EQ), calculated by dividing brain weight by body weight. Using this parameter, a mouse is considered more encephalised than a modern human. We possess an EQ of 0.015, while rodents score up to ten times higher, around 0.1. In other words, the brain-to-body weight ratio is higher in rodents and other small mammals than in larger ones like ourselves. The slope correlating brain and body weight follows distinct patterns across these groups. Ultimately, EQ proves insufficient in determining which species possesses the most developed brain.

A new parameter was therefore established: the Encephalisation Index (EI). This divides the observed EQ by the estimated EQ for specific taxonomic groups. The resulting value is then compared against the regression line for the entire group to determine whether it lies above or below the norm. In this way, the EI of primates can be analysed independently of other mammals, which display different rates of brain and body growth. If the EI exceeds 1, the species is considered to have a larger-than-normal brain—i.e. encephalised. If it falls below 1, the opposite holds true. Australopithecus africanus and afarensis registered around 1.3, Paranthropus species around 1.5, Homo erectus and related forms about 1.9, most cetaceans around 2, and modern humans score approximately 2.9. Based on these calculations, modern Homo possesses a brain roughly three times larger than the average within its evolutionary group. Thus, encephalisation is not a conceptual artefact; mathematics confirm that we possess a disproportionately large brain. All that remains now is for each of us to use it effectively.

Source: educational EVIDENCE

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