# Evolution of human intelligence

## Part 1. Biology

You should ask the biology component of this elsewhere obviously, but any story here must start with biology, so one obligatory links: [evolution of the human brain](https://en.wikipedia.org/wiki/Evolution_of_the_brain#Human_brain).

["The trend [towards larger brains] was caused primarily by evolution of larger brains within populations of individual species [of human ancestor], but the introduction of new, larger-brained species and extinction of smaller-brained ones also played a part."](https://www.uchicagomedicine.org/forefront/biological-sciences-articles/brain-size-of-human-ancestors-evolved-gradually-over-3-million-years)

In other words, we evolved our brains mostly through sexual selection, kin selection, etc, not so much through punctuated equilibrium.

We created basic sharp rocks like 3 million years ago, but our ancestors must have used naturally sharp rocks long before that. See https://phys.org/news/2025-03-hypothesis-stone-tools.html

We developed fire and bone tools 1 million years ago, developed simple wooden spears and huts like 400k years ago, and only developed clothing 170k-300k years ago, so relatively unformed sticks and sharp rocks were our only tools for almost all of our evolutionary history.

Is a sharp rock better than sharp claws or sharp teath? If so, why? It's harder and more easily replacable, but it's not always convenient. I suppose the teath being flatter helps eat plant foods, so then the sharp rock helps eat meat too.
Importantly, sharp rocks allow eating bown marrow. There is debate over when humans started eating meat though, but australopithecus ate very little if any meat, while neanderthals did a million or so years later.

https://www.earth.com/news/early-humans-had-surprising-diets-3-5-million-years-ago/

https://www.calacademy.org/press/releases/scientists-discover-oldest-evidence-of-stone-tool-use-and-meat-eating-among-human

All together, we've imho quite a hard time justifying this increase in brain capacity from tools alone, like people often do. It's possible strategy played some major role, either in conflicts between tribes, or later in hunting, but again see the meat consumption debate.

Animals communicate & learn about poisonous plants quite effectively, but maybe humans could migrate faster. I suppose birds can migrate easily because poisonous berries typically only harm mammals, not birds. I'd also worry human intelligence makes us more vulnerable to poisonous plants (another discussion).

At least to me, all this says we need a different "primary" evolutionary driver of human intelligence, because alone tool usage and strategy cannot really suffice. I hinted at the answer above, sexual selection.

Human intelligence need not serve any physical fitness purpose, maybe intelligence simply helped us choose mates and do family politics? Intelligence could be originally be a peacock tail, an accessory that allows us to impress mates, to judge mates, and to negotiate with family members.

Afaik [cetaceans](https://en.wikipedia.org/wiki/Cetacean_intelligence) and [elephants](https://en.wikipedia.org/wiki/Elephant_cognition) only really use their intelligence socially. I suppose our tool use could helped differentiate our intelligence from say elephants more emotional intelligence, which then triggered even more sexual section through symbolic intelligence, ala poetry.

Anyways..

Do not assume our intelligence serves our physical fitness. Sexual selection has an unparalleled power to create artificial niches where no physical fitness requirement exists. If our intelligence is firstly and formost a mating dance, then there is no physical reason other animals should similarly evolve so far towards intelligence.

## Part 2. Holocene climate

As you asked this in anthropology, there are two more obligatory links: [anatomically modern humans](https://en.wikipedia.org/wiki/Early_modern_human) vs [behaviorally modern humans](https://en.wikipedia.org/wiki/Behavioral_modernity). We think biological intelligence remained similar for the past hundreds of thousands of years. If anything, modern pollution & specialisation lowers modern human intelligence vs ancient human's intelligence.

We only developed agriculture, irrigation, modern society, and more advanced tools during the holocene, meaning the previous 11k years, when the global climate became abnormally stable.

We could exploit the holocene so fully only because of our biological intelligence, but without the holocene humans would never have the energy surplus to so exercise our intelligence, and we'd still be small tribes of hunter gatherers.

Now..

We've ended the holocene through our usage of fossil fuels. It's likely advanced human society remains quite a while longer, but if planetary boundaries like climate change disrupt our society too much, then humans might survive, with our current intelligence, but might never again create major civilisations. We could later evolve away from general intelligence and towards narrower more specialised intelligence. The peacock tail fades when sexual selection loses interest for whatever reasons.