Your brain is the product of 3.5 billion years of intense evolutionary pressure, including 2.7 million years as tool-using hominids and over 100,000 years as homo sapiens.
Human DNA is about 98-99% identical to chimpanzee DNA. But that crucial 1-2% difference is mainly the genetic factors affecting the brain – especially for its relationship functions. In fact, the latest science suggests that the evolution of the brain was driven in two steps having to do with the survival benefits of strong relationships.
First, among vertebrates, many bird and mammal species developed pair bonding as a way to raise children who survived. (Remember that fish and reptiles generally do not raise their young and may in fact eat them if they happen upon them soon after they hatch.)
The “computational requirements” of choosing a good mate, working things out together, and then raising young to survive – hey, it’s just sparrow and squirrel couples, but anyone who has raised kids knows what I’m talking about – required larger brains than those of reptiles or fish that dealt with similar environmental challenges but made their way in life on their own.
By the way, it may be a source of satisfaction to some that polygamous species usually have the smallest brains.
Second, building on this initial jump in brain size, among primate species, the larger the social group, the bigger the brain. (And the key word here is social , since group size alone doesn’t create a big brain; if it did, cattle would be geniuses.)
In other words, the “computational requirements” of dealing with lots of individuals – the alliances, the adversaries, all the politics! – in a baboon or ape troupe pushed the evolution of the brain.
In sum: More than learning how to use tools, more than being successful at violence, more than adapting to moving out of the forest into the grasslands of Africa, it was learning how to love and live with each other that drove human evolution!