It’s all about the encephalization, really. Millions of years ago our hominid ancestors stumbled onto a novel adaptive strategy: be smart, adaptable, and capable of learning rather than purely instinct-driven. Make tools; use fire; invent language.
This strategy required much, much more of our nervous systems. Because intelligence was in fact a winning strategy, we were selected for growing more complex brains capable of doing more information processing. But increasing the logic density of brains is hard; there probably isn’t a path to it through the design space that is rapidly exploitable by small point mutations. So selective pressure made our brains larger, instead.
The fossil record shows that the hominid line encephalized at a breakneck speed compared to the usual leisurely pace of evolutionary change. This had huge consequences; much of human biology is a series of hacks and kluges to support that encephalization, often in stupidly suboptimal ways.
The one that’s relevant here starts from the limited width of the birth canal. Limited, that is, by the pelvic girdle surrounding it. A skull that’s too large won’t fit through. Therefore, the genetic lines that survived were those in which babies are born with small skulls but the ability to grow them much larger by maturity. (And even so, the size of a baby’s skull pushes that limit pretty hard; this is why birth is so much more difficult and dangerous for human females than it is for other primates).
That design (be born with a small skull and upgrade it outside the womb) implied a long juvenile period between birth and physical maturity. In fact the human brain doesn’t completely finish configuring and rewiring itself until around age 25. And the long juvenile period probably also explains the exceptionally long human lifespan; whatever had to be altered in the development clock to defer stabilization into the final adult configuration probably also delayed the inset of senescence. (Direct evidence for this theory is the rare disease “progeria”).
And the dominoes kept falling. The long juvenile period implied offspring that would be incapable of fending for themselves for an unprecedently long time – on the order of decades rather than the few months to a year typical for other mammals. Consequently the selective value of extended cooperation between the parents went way, way up relative to even our nearest animal kin.
Romantic love works as an an evolved mechanism for keeping mated pairs cooperating long enough to raise multiple children. Here again, selection favors those who love more because they get to launch more offspring. We are, in fact, made to fall in love – and it would only be surprising if the mechanism for establishing it were not simple, robust, and easily triggered.
Eric S. Raymond, “Love is the simplest thing”, Armed and Dangerous, 2015-01-15.
June 14, 2016
QotD: Romantic love … what is it for?
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