Our brains don’t seem all that special when you compare their relative size to that of our closest animal relatives. To understand human intelligence, scientists are now delving into new areas of research.
Arthur Keith was one of those researchers who turned out to be wrong about many of the things they said. Prominent anatomist and anthropologist of the early 20th century, he was an advocate of scientific racism and opposed racial mixing.
At least partly because of his racial views, he was convinced that humans originated in Europe, not Africa, as is now universally accepted.
And he was a strong supporter of the so-called Piltdown Man, a notorious hoax involving fake fossils.
Keith also described a notion that became known as the brain Rubicon. Noting that humans have larger brains than other primates, Keith argued that human intelligence only became possible when our brains reached a particular threshold.
For Homo, the genus to which we belong, Keith thought the minimum volume was about 600-750 cubic cm. For our species Homo sapiens, it was 900 cubic cm. If it were smaller, the argument goes, the brain would not have enough computing power to support human reasoning.
It is true that Homo sapiens, as a species, has a large brain. But what this means it’s starting to be seen differently. Paleoanthropological evidence suggests that some species, such as Homo floresiensis and Homo naledi, had complex behaviors despite having rather small brains.
However, evidence is also emerging from the fields of genetics and neuroscience that Brain size is far from the only factor that determines intelligence.
Changes in the brain’s wiring diagram, in the shape of neurons, and even in when and where certain genes are activated are all equally important, if not more. So, size is not everything.
The smart ones with small brains
It is true that the human brain is unusually large. This remains true even if we compare the size of the brain to the size of our body.
«Humans are by far the primates with the largest brains«says neuroscientist Martijn van den Heuvel, from the Free University of Amsterdam, in the Netherlands.
It is also true that if you look at the last six million years of human evolution, there is a trend towards increasing brain size.
Early hominids, such as Sahelanthropus and Australopithecus, had relatively small brains, but early Homo species had larger brains, and the brains of Homo sapiens are even larger.
However, when you look closer at the details, the story is not so simple. Two species stand out for their unusually small brains: the Homo floresiensis, also known as the true “hobbit”, and Homo naledi.
Homo floresiensis was first described in 2004. It was only one meter tall and lived on the island of Flores, Indonesia, for the past several hundred thousand years. It became extinct at least 50,000 years ago.
The first specimen had a brain that measured only 380 cubic cm or perhaps 426 cubic cm, putting it on par with chimpanzees.
There is strong evidence that Homo floresiensis made and used stone tools, as did other species of Homo. Early studies also reported evidence of burning, suggesting they had control of the fire.
But subsequent analysis indicated that all the fires were lit less than 41,000 years ago, suggesting they were the product of modern humans.
However, the stone tools alone are evidence that Homo floresiensis behaved in a way that chimpanzees could not.
A decade later, researchers in South Africa described Homo naledi.
The remains were found deep in the Rising Star cave system, which can only be reached by experienced cavers. Like hobbits, Homo naledi had a small brain, and also lived recently, between 200,000 and 300,000 years ago.
Fuente: BBC Future