The Perplexing Human Brain

The mental arms race amplifier

Modern humans possess a mental capacity that far exceeds the minimal requirements for basic survival. It exceeds the minimal requirements for tool use in hunting and gathering, too. Chimpanzees, for example, are now known to use quite a variety of tools. There is also evidence that our small-brained “ape-man” ancestors (the Australopithecines) were using stone tools to extract bone marrow more than two million years ago.

If our ancestors simply needed to hunt, gather, and fashion rudimentary stone tools, why did evolution produce a brain capable of creating quantum mechanics and beautiful symphonies?

A clue to the solution of this puzzle is provided by the curious slow-fast-stop pattern in the evolution of increased brain sizes: a long, sluggish period of increase as tool use was first adopted, followed by a frantic burst of rapid growth chiefly over the last million years, ending in our contemporary evolutionary plateau in intelligence.

To solve this paradox, we must look beyond simple survival and explore three major competing theories for the Why of human evolution: (1) the Ecological Adaptation Hypothesis, (2) the Intraspecific Competition Hypothesis, and (3) their ultimate synthesis—the Mental Arms Race Amplifier.

Theory I: The Ecological Feedback Loop

The Ecological Adaptation Hypothesis suggests that tool use triggered a positive feedback selection mechanism. In this model, as early hominids began using tools to dig up food, kill prey, cut up carcasses, and defend themselves from predators, those with slightly better manual dexterity and the mental capacity to improve those tools gained a fitness advantage. This created a cycle: better tools provided better resources, which in turn increased the selection pressure for the very traits—like brain size—needed to master those tools.

The Price of Intelligence

However, a larger brain is not a free lunch. Evolution has to balance this intelligence against severe biological taxes.

Childbirth Hazards: The mechanical difficulty and increased mortality risk of birthing infants with large craniums.

Infant Helplessness: To accommodate brain growth, human infants are born early in developmental terms, leading to a prolonged period of vulnerability and total dependency that requires intensive parental care. Sometimes well into graduate schooling.

Evolutionary Insight: The Variance Problem

While the ecological theory is intuitive, it struggles with the lack of “racial” scale differences between human populations. If ecology were the primary driver of intelligence, we would expect human mental ability to vary significantly according to the demands and tool-using opportunities of the environments that human populations inhabit.

For example, there should be different selective opportunities in very different environments. Populations that inhabit rain forests should have different opportunities, costs, and benefits from tool use compared to populations that inhabit tundra near the North Pole. This should then produce differences between the intelligence levels of human populations that are comparable to their differences in skin pigmentation.

Instead, we find that the variance in potential mental ability between distinct breeding populations is remarkably small compared to the variance found within those populations. If ecological problem-solving were the only sculptor, the mental floor of our species would be much more dependent on the environments that populations have inhabited for many generations than the universal high-performance engine we see today.

There is No Heart of Darkness

If I may be forgiven a story in the style of Joseph Conrad, the following anecdote was told to me by a former American Ambassador to a tropical country.

Soon after his arrival to this country, which I will not name, the Ambassador was told that he would have to upgrade his telecommunications equipment so that he could securely communicate with the State Department in Washington, DC. Fortunately, he was assigned a very competent young man to assist him, an employee at the Embassy who was a member of the local population.

A few days later, the Ambassador was offered the opportunity to take a boat upriver, away from the capital city on the coast. He was escorted by other staff members who were also locals. As the boat proceeded upstream, what amazed the Ambassador was how quickly the riverbanks transitioned from urban settlements to suburban areas to completely overgrown rainforest.

After a while, the riverbanks occasionally featured local tribespeople wearing almost nothing but carrying spears. This made the Ambassador a bit fearful, because his boat was not particularly large, and it had very little in the way of cover.

Then the engine of the boat began to sputter. The pilot steered the boat on to the riverbank, and moored it there. He got out to work on the engine.

Soon tribespeople emerged from the jungle, and surrounded the boat. The Ambassador began to fear for his safety.

Fortunately, one of his assistants was fluent in the language of these tribespeople. The assistant got out of the boat, and spoke with animation to the oldest man in the group that surrounded the boat.

The assistant then returned to inform the Ambassador that the tribal elder would be happy to help them, because he had heard about the Ambassador from one of his nephews, who worked for the Ambassador on the telecommunications link with Washington.

This is not the pattern of cognitive differentiation that would be expected if human populations were dramatically different in cognitive abilities, because of the different ecologies that they have supposedly adapted to.

Theory II: The Social Chess Match

If the environment doesn’t solely establish selection for high intelligence, perhaps our peers did. The Intraspecific Competition Hypothesis shifts the focus from “Hominid vs. Nature” to “Hominid vs. Hominid.”

This theory proposes that tool use—specifically the invention of weapons—radically altered the rules of survival. Weapons are equalizers. They are hand-held rather than built-in, meaning a smaller individual with a better spear or a clever ambush plan using some novel weapon could defeat a physically stronger rival.

In this selection regime focused on within-species conflict, cunning is the ultimate Darwinian currency. Reproductive success requires strategic facility: the mental capacity to (a) invent weapons for tribal warfare, (b) imitate the successful social tactics of others, and (c) navigate complex social alliances.

This competition functions like an “Evolutionary Game Auction”, a type of evolutionary game conflict that includes the famous “War of Attrition” which John Maynard Smith discussed in a 1974 Journal of Theoretical Biology article on evolutionary game theory. In these auctions, contestants “bid” energy, time, or risk. However, these bids carry overshoot costs—real physiological investments that cannot be wholly recovered after victory.

Just as a male bird might pay a metabolic tax to grow elaborate plumage to “out-bid” a rival for a mate, hominids investing in brain tissue and its use must have paid a tax in the metabolic costs of increased amounts of brain tissue. And like the costs of the peacock’s tail, this evolutionary theory assumes that the benefits of increased social intelligence are confined to the social arena.

The Limit of Competition

The empirical weakness in pure social-competition theories of human brain evolution is their implied, eventual, evolutionary equilibrium states. In a game of pure strategy, you would expect a population to eventually settle into a mix of types: a few high-investors and a large number of “low-cost” individuals with Australopithecine-level abilities who survive by simply not paying the high metabolic price of a large brain. [This is a mathematical result obtained by Jon Haigh and myself in a 1980 Journal of Theoretical Biology article called “Evolutionary game auctions”.]

Because modern human populations possess a high minimum of intelligence [leaving aside rare genetic disorders and trauma], social competition alone cannot be the full story of human evolution. Our evolution requires a selection mechanism that prevents low brain-investment strategies from succeeding.

Theory III: The Mental Arms Race Amplifier

The Mental Arms Race Amplifier Hypothesis provides the missing elements that can solve the puzzle of our giant brains. It posits that while ecological pressures established the initial functional minimum for intelligence, the social arms race acted as an accelerator that drove the species past the point of our ape-man ancestors of two million years ago.

[The following explanation is adapted from my 1980 article, “The Mental Arms Race Amplifier,” published in Human Ecology.]

This theory solves the null-investment problem by combining both ecological and social selection pressures. Crucially, the rise of human culture did not mitigate this mental arms race; instead, it fueled it by amplifying the complexity of weapons use—from fire-starting to tactical warfare—further fostering the value of increasing brain investment.

At the core of the mental arms race amplifier model is that sometimes increased brain investment is beneficial ecologically, and sometimes it isn’t. But increased brain investment in “social chess” (think Machiavellian strategems) is always beneficial reproductively, yet always has a physiological cost.

The magic happens when brain functions are NOT modular, focused solely on either ecological or social benefits. Brain investments which benefit BOTH ecological and social functions can undergo combined ecological and social selection, producing an amplification effect for the evolution of social or Machiavellian intelligence.

The Logic of Superamplification

“Superamplification” occurs when the ecological fitness benefits to increased brain investment are positive. In this case the environment further fosters the mental arms race, increasing investment in brain functions which can be used in both social and ecological arenas. The mental arms race becomes, in effect, unpaid or cost-free.

Under these particular conditions, mental arms race selection can proceed without being checked by immediate survival penalties, fostering the evolution of brain investment with unprecedented speed. This explains the explosive middle period of brain evolution in our Homo ancestors, when hominid species massively invested in cognitive hardware because the ecological bank account was full enough to allow it.

The Legacy of our Mental Arms Race

The story of the human brain is a trajectory of escalating general intelligence. We began with a slow increase in brain size driven by the basic demands of tool-assisted survival, the pattern of the early Australopithecine phase of our evolution. This was followed by a massive surge where social competition was amplified by ecological benefits, leading to the rapid increases in hominid brain size which occurred between 1.5 and 0.2 million years ago.

Human populations have now reached a modern equilibrium not because the mental arms race has ended, but because we have hit physical and metabolic limits of the evolutionary game auction for increased general-purpose intelligence. This generalized intelligence and our vast capacity for language are not merely tools for finding food; they are the high-performance products of selection mechanisms that acted powerfully ONLY on generally useful brain functions, of value in a wide range of contexts.

Final Thought

This theory for human evolution is primarily anti-modular. The study of the behavior of almost all other animals appropriately interprets them in terms of specific selection mechanisms arising from specific ecological or social challenges.

But humans are qualitatively different. I believe that, instead of our behavior being closely machined by natural selection to specific contexts, we have evolved a type of free will. Not existential or cosmological free will. Rather, a kind of Darwinian free will, which enables us to solve our material and social problems in an open-ended manner.

The implications of the mental arms amplifier theory will be one of my main topics in the material that I will be providing to paid subscribers going forward. I believe that those implications are profound. Even exciting.