Giant Brains Are Rare

In Sapiens, Yuval Noah Harari explains that Homo sapiens means wise man. It is a term we have given ourselves as a species because we have large brains and use those large brains to set ourselves apart from the rest of the animals and creatures on the planet. There are some other species with big brains, but in general large brains are rare, and no other species has been shown to use their brain to the same competitive advantage as humans.
But if large brains have made us so competitive across the globe, why are they so rare? Harari writes, “The fact is that a jumbo brain is a jumbo drain on the body. … in Homo sapiens, the brain accounts for about 2-3 percent of total body weight, but it consumes 25 per cent of the body’s energy when the body is at rest. By comparison, the brains of other apes require only 8 per cent of rest-time energy.”
Our brains are incredibly active and use a lot of sugars for fuel, even when we are not doing anything. This is great news for those of us who are trying to go on a diet to lose some weight today, but it was not great news for our ancestor hunter-gatherer humans and proto-Homo sapiens species of the past. According to Harari, large brains essentially have a high up-front cost. There is a large energy up front energy cost that goes into maintaining the brain before a species can really use the brain to a competitive advantage, and that has been a barrier to other species developing large brains and using them in a way that could give them a competitive advantage.
Harari continues, “Archaic humans paid for their large brains in two ways. Firstly, they spent more time in search of food. Secondly, their muscles atrophied. … A chimpanzee can’t win an argument with a Homo  sapiens, but the ape can rip the man apart.” Strong thinking and reasoning skills are helpful today and are the reasons we live in houses, build rocket ships, and are able to develop vaccines to end global pandemics. However, our big brains are not always the best tool to bring to a fist fight. It is not obvious that better reasoning skills will help a species survive better than sharp claws and teeth, thick hides, or spiky spines. Evolution doesn’t have an end goal in mind, and for all species besides the human species that evolved into Homo sapiens, the big brain payoff simply wasn’t the evolutionary rout that provided the best chance of survival and spread. It wasn’t until the big brained human species began to live and interact in clusters and tribes, communicating and working together, that big brains and reasoning skills could begin to pay off and become competitive against larger animals with bigger muscles and more ferocious claws, teeth, and tusks.

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