Origins of human intelligence

Here is a plot of hominid brain volume over the last 10 million years:

1

i.e. brains got 10 times bigger, with most of this happening in the last 2 million years after a sudden changepoint. So… what’s that elbow? What got the engine of human intelligence going?

OK, as we should have guessed, it’s Homo.

**At this point we enter the deeply fun and underdetermined world of what-if evolutionary storytelling**

But what about him?: what does early Homo start doing differently, 2mya?

(Logically, whatever it is must have increased our ability to get calories. If it didn’t, we couldn’t have “funded” the bigger brains.)

Up to co

: He goes upright. The literal ascent of man, off his knuckles!

What’s the big deal about bipedalism?

There’s a few things, like that it reduces your body’s insolation cross-section -> the sun heats you less -> you stay cooler -> you can run longer -> much better persistence hunting.

But one huge one is it frees up your hands so you can carry stuff and throw it. (And you can start adapting muscles for throwing specifically. The human shoulder is biologically unique as a result.)

This quickly completely transforms human society:

• Let us throw stones. Means you can more-safely attack people who are stronger than you;
• That new safety makes it far easier to build a coalition of risk-averse weaker lads to overthrow tyrants;
• The new possibility of overthrowing bullies means you have a very powerful incentive for better intelligence: coalitional intelligence.
• So pure physicality falls, supplanted by sociality. “the reversal of dominance hierarchy”; Erectus society was probably reverse-dominance. The first time, of many, that the ~samurai class fell.
  • Gracilisation. This in turn allows reallocating resources from muscles (and skeletons) to brains. Erectus is bigger than habilis but less muscular per weight; sapiens is smaller and less muscular.
• This in turn actually increases intra-group competition, since social skill, coalition-building, and scheming are less fixed traits than Being Big and so more open to entrants. Now everyone needs theory of mind.

Co to cal

OK, but how does this get you more calories?

Well, throwing spears are insane tech in the prey-animal meta. They still haven’t really adapted to it. But more than that, social intelligence and theory of mind makes you a better pack hunter. This lets you break the game with things like buffalo jumps. And that’s before the new tech produced by your new intelligence really starts accumulating.

We can build up a graph of guesswork on top of this sound basis:

Going upright is then a main cause of the most recent intelligence explosion, us.

(I am sympathetic to the view that the central node here is “cumulative culture” and not “intelligence”. If you have intelligence you don’t need so much muscle; if you have culture you don’t need so much intelligence; if you have X you don’t need so much culture.)

(Henrich)

Cal to mesaoptimisation

The above only takes us up to the beginning of culture as we know it. Some other stuff happened in the last million years which doesn’t fall out as a leap in brain volume. (We got as big as we could, but I don’t know whether the obstetric dilemma is what forced evolution to switch to cultural evolution instead of brain scaling.)

• Something huge began 40 kya.

• More people -> more mutations -> more change + selection -> more tech -> more calories -> more people

• Domestication and coevolution with plants and animals. Start to bend all of nature to our needs. And most of all self-domestication.

• and most of all writing (4 kya), which started a second coevolution loop less dependent on individuals. It also massively increased the graph connectedness, since a person’s technologies could spread after their death and far beyond their geography.

• then some other stuff

• And so you are a violent and irrepressible miracle. The vacuum of cosmos and the stars burning in it are afraid of you.

So

Be proud! Become what you are! Stand tall! Stand tall!

This post is just a lightning talk version of theories by Boehm, DeSilva, Hawks, Shulman.