In a earlier post, I wrote that even though life should be very common all over the universe, intelligence should be rather rare. I want to elaborate a bit more on this point, to show how the emergence of intelligent life on Earth was more a matter of chance than of necessity.
The most singular feature about a cultural species like ours is the fact that millions of other species acting by instinct prove that it is more advantageous to live without culture. Then, what were the conditions that favored the evolution of a cultural species?
Among the several hypothesis floating around, there is one due to Peter J. Richerson and Robert Boyd that it is quite appealing. They proposed that an environmental factor may have triggered the process: the fast climate variations in the Pleistocene, the geologic epoch that lasted from 2.5 million to 12.000 years ago.
Humanoids have lived on Earth for 7 million years, but the brain increasing deviating from other primates started 2 million years ago, coinciding with a period of climate variations so abrupt that could make a glacial region to become warm in a period of one or two centuries.
From an evolutionary point of view, such variations may have large implications for definition of the best survival strategy. We can think of two limit cases: in one extreme, they are so slow that the organisms may adapt to the new conditions by natural selection; in the other extreme, they are so fast that it is advantageous to have single individuals inventing survival techniques. If the climate variations are fast, but not extreme, a mix of invention and imitation by other individuals may be the optimal survival strategy, creating the seed for propagation of cultural variants spanning many generations.
Naturally, if climate variations were alone responsible for culture, we would have many other cultural species around. In fact, fast increase of brains during the Pleistocene happened not only to human, but also to many other mammals. Still, culture became ultimately essential only to humans. This means that several other factors may have been in play to produce a cultural species.
One of them was, for sure, the ability of maintaining a costly large brain, which was possible only because the Homo Erectus learned how to cook. Indeed, if we followed the diet of other primates, we would have to spend 9.5 hours per day eating!
We are so used to see ourselves as a cultural species that we should be careful to not forget that what we are now is a consequence of our evolutionary history. In no way the appearance of intelligence on Earth seems to be a biological necessity.
Were this history a bit different, say, if the Homo Erectus did not dominate the fire, humanoids might have ended up as gatherer primates, acting mostly by instinct and split in many subspecies spread over the planet.
Even supposing that humans evolved into cultural beings, there were no need that they would become sedentary. Were the geography of the planet distinct, with several small continental plates like Oceania instead large masses like Eurasia, the hunting-gathering strategy might have predominated, as it did among several isolated human groups.
Then, agriculture would not have emerged, cities would never been built and I would not have written this text.
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