Tag Archives: Primate

Whence Better Brains?

By Robin Hanson · July 27, 2011 10:00 am · Comments (8)

The cover story of the July Scientific American is on brain physics. It persuades me that raw brain hardware was more important than I’d thought in our history.  Here is my current best guess on brain history.

Across diverse species we see strong convergence in brain organization, especially conditional on brain size. Species differ more in their brain hardware components, and their energy sources. For example, primates have innovative cell designs allowing higher neuron density. Given access to such cells, primates could afford to evolve bigger brains, and then bigger pair-bond-based social groups.

Humans found a way to use big primate brains to support big-group far-traveling long-life versions which could access richer energy sources, which in turn supported large energy-hungry brains. Humans found a way to use those huge old social brains to support robust accumulation of culture, which is our main advantage over other primates. This was probably supported by only minor changes in brain organization.

While the brains of smarter humans today may use a better set of long term connections, probably most of their advantage comes from using more energy-intensive brain hardware. So it probably wasn’t until our recent cheap energy era that high IQ humans gained large advantages. The tendency 0f smarter humans to choose lower fertility lowers their advantage today.

Many quotes from that article: Continue reading "Whence Better Brains?" »

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Travel Made Humans

By Robin Hanson · June 20, 2011 9:00 pm · Comments (25)

I hadn’t till now appreciated how central long distance travel was to early human evolution. A 2004 Nature article:

No primates other than humans are capable of endurance running. … Well-conditioned human runners … can occasionally outrun horses over the extremely long distances that constrain these animals to optimal galloping speeds, typically a canter. … Horses have … narrow ranges of preferred speeds for trotting and galloping and gait transitions that minimize cost. … Human runners differ from horses in employing a single gait. … Humans are thus able to adjust running speed continuously without change of gait or metabolic penalty over a wide range of speeds. …

Considering all the evidence together, it is reasonable to hypothesize that Homo evolved to travel long distances by both walking and running… Endurance running is not common among modern hunter-gatherers, who employ many technologies to hunt (for example, bows and arrows, nets and spearthrowers), thereby minimizing the need to run long distances. But Carrier has hypothesized that endurance running evolved in early hominids for predator pursuit before these inventions in the Upper Palaeolithic (about 40kya). Endurance running may have helped hunters get close enough to throw projectiles, or perhaps even to run some mammals to exhaustion in the heat. …

Another hypothesis to explore is … in the open, semi-arid environments … early Homo may … have needed to run long distances to compete with other scavengers, including other hominids. … Similar strategies of ‘pirating’ meat from carnivores are sometimes practised by the Hadza in East Africa. … It is known that major increases in encephalization occurred only after the appearance of early Homo. … Endurance running may have made possible a diet rich in fats and proteins thought to account for the unique human combination of large bodies, small guts, big brains and small teeth.

A 2009 Evolutionary Anthropology article on “The Emergence of Human Uniqueness”

Important preadaptations in the genus Homo … led to human uniqueness. First, hominins are bipedal and, as a result, cover geographical ranges far larger than other apes do. Even hunter-gatherers living in tropical forests have daily home ranges that are two to three times those of chimpanzees, and lifetime home ranges more than two orders of magnitude greater. Thus, individual hominins faced more environmental variability than do chimpanzees. … This would favor social learning capacity.

Second, bipedal hominins evolved exceptional manual dexterity because their hands were freed from locomotory constraints, and they could carry tools with little cost. This would have favored increased tool using and making behavior and probably increased selection pressure on imitative capacities as well. Third, by at least 2 million years ago, hominins had begun to depend on high-quality, widely dispersed resources that were difficult to obtain. This shift of feeding niche had important life-history implications. Juveniles could not fully feed themselves due to the complexity of the extractive niche, and this led to their provisioning by close kin. As large package foods became common, the foods returned to the juvenile home base were probably ‘‘shared’’ by coresidents. This …. might partially explain why hunter-gatherers experience early adult mortality at one-fifth the rate of wild chimpanzees. That pattern would favor a life history with later age at maturity and delayed onset of senescence. … Continue reading "Travel Made Humans" »

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What The Eyes Say

By Robin Hanson · March 23, 2011 8:00 am · Comments (23)

Compared to other primates, human muscles are rather weak. In hand to hand combat with a chimp, humans don’t stand a chance. It seems that because we are so good at using tools, we could avoid paying for expensive muscles. Similarly, compared to other animals, language lets humans talk more precisely, and talk about things not in our immediate view. So you might expect we’d get worse at non-language communication. You’d be wrong:

Humans are known to have the largest and most visible sclera – the “whites” of the eyes – of any species. This fact intrigues scientists, because it would seem actually to be a considerable hindrance: imagine, for example, the classic war movie scene where the soldier dresses in camouflage and smears his face with green and brown pigment – but can do nothing about this conspicuously white sclera, beaming bright against the jungle. There must be some reasons humans developed it, despite its obvious costs. In fact, the advantage of visible sclera – so goes the “cooperative eye hypothesis” – is precisely that it enables humans to see clearly, and from a distance, which direction other humans are looking. … Chimpanzees, gorillas, and bonobos – our nearest cousins – follow the direction of each other’s heads, whereas human infants follow the direction of each other’s eyes. (The Most Human Human, p. 39).

Note that most of what we learn via looking at each other’s eyes is hard to verifiably say via language. You might feel he is laughing at you with his eyes, but it will be hard to make that laugh the basis of a group response – others probably didn’t see his eyes at the right moment, or might interpret what they saw differently.

Language was a big innovation, but my homo hypocrites hypothesis is that we humans are now actually post-language in important ways. Language let us express and enforce social norms, but we’ve since developed powerful capacities to coordinate outside the scope of language, to evade those norms. The whites of our eyes seem a key part of that norm-evading capacity.

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Sex At Dawn Is Right

By Robin Hanson · October 12, 2010 4:00 pm · Comments (73)

I like to think of myself as courageously seeking out important truths, however uncomfortable. But like most would-be-courageous folk, I don’t really know what I want until I get it. I was excited to read the contrarian Sex at Dawn, which suggests sexual promiscuity is our forager heritage. But that pretty sparkler was really a grenade – its uncomfortable truths shook me to my core.

To hear a different view, immediately afterward I read Evolutionary Biology of Human Female Sexuality [EBoHFS], which supports a standard view of foragers as long-term pair-bonders. By comparison, EBoHFS is more academic: dry, clinical, verbose, and careful to define terms and consider many possibilities. It reviews an immense number of studies, and appears to takes a cautious middle ground.

Sex at Dawn, in contrast, frustrates academic sensibilities. It is passionate, partisan, even snide. It doesn’t systematically review evidence pro and con, or points of view, and it takes long detours to settle scores with opponents. It is long on anecdotes and examples, relative to systematic data. Its authors are confused on how economists use “selfishness”, and on basic Malthusian population theory; they aren’t really to be trusted on theory. Furthermore, their relationship advice seems flippant.

But on their key claim, that forager females were sexually promiscuous, I am persuaded: they are basically right. EBoHFS hardly offers any contrary evidence, it just keeps repeating that evidence is ambiguous, while embracing the usual story by default. (Sex at Dawn also gets forager peacefulness right – see Chapter 13.)  Searching for expert critical reviews, the closest I found were this and this, which mainly just complain it is all very complex and no simple generalizations apply.

The basic facts are these. Recent humans mostly had long-term pair-bonds, while our two closest primate relatives, chimps and bonobos, are quite sexually promiscuous. Yes, they hardly mate at random, and may return often to favorites. Even so:

“Among chimpanzees, ovulating females mate, on average, from six to eight times per day, and they are often eager to respond to the mating invitations of any and all males in the group. … A recent study … showed that more than half the young (seven of thirteen) had been fathered by males from outside the female’s home group.” [p70]

Bonobos females are even more promiscuous. In fact, to find biological analogues to recent human monogamy, EBoHFS looks to various kinds of birds; mammals won’t do. “Monogamy is not found in any social, group-living primate.” [p64]

The big question then is when did the biologically-rare (3% of mammals) phenomena of (near) monogamy arise in our lineage, millions of years ago with the rise of humans, or ten thousand years ago with the rise of farming? And since our data on modern foragers suggests that farming at least greatly reduced promiscuity (especially for females), the big question is really whether lightning struck once or twice, i.e., if there were one or two big unprecedented moves away from typical social-primate promiscuity. Occam’s razor suggests one lightning strike.

If human sex were like chimp and bonobo sex, how should we expect it adapt to human changes, like larger brains, group sizes, and lifespans, and more egalitarian sharing? Dunbar says brain size, group size, and grooming time fraction correlate, and says language let humans better “groom” our record size groups. If sex was part of “grooming”, we’d expect humans to spend a record fraction of time on sex. We should also expect more adaptations to longer term relations (like pedophilia).

So what is the data? Humans spend more time having sex than any known species. Human sex shares many otherwise-rare features with the promiscuous bonobos, who hide their fertile days and have sex all month long, in many positions including missionary where they gaze into each other’s eyes and kiss deeply. Bonobos share food with sex, and use sex for social bonding, such as via homosexuality. Human sex has many other features understandable as adaptations to promiscuity, including large external testicles, a record size penis designed to scoop away other semen, men preferring high male-to-female ratios in porn, long frequent sex, and women being louder and lasting longer than men.

Monogamy vs. promiscuity is a rare area where academics and cultural elites tend to favor the conservative/farmer side of the forager vs. farmer divide. While I find myself balking at the idea of embracing sex partners with forager promiscuity levels, I accept that this preference was culturally imprinted on me.

Many Sex At Dawn quotes below the fold: Continue reading "Sex At Dawn Is Right" »

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Hail Christopher Boehm

By Robin Hanson · May 27, 2010 6:20 pm · Comments (24)

Evolutionary psychology is a powerful set of ideas, from which I’ve drawn great insight over the last decade or so.  But like most of its fans, I didn’t realize I was missing half of the story.  You see, academic anthropology departments have long been split into two warring camps: physical vs. cultural anthropology.

Physical anthropologists include folks who dig up old skulls, and who work with animals like chimps. Cultural anthropologists focus on studying humans in diverse societies, and are more hostile to evo psych. From a review of  Evolutionary Thought in Psychology: A Brief History:

Cultural anthropology was a different story. Raw self-interest and out-group hostility played a larger role. Plotkin argues that the rise of cultural anthropology was, in no small measure, a reaction against evolutionary approaches in the social sciences. On the one hand, it was a classic turf war. Cultural anthropologists feared that an evolutionarily based social science would put them out of business, and this motivated them to drive out the evolutionary infidel. On the other hand, many leading cultural anthropologists, particularly Franz Boas and his students, who were distrustful of the theory of natural selection. They argued that cultural expressions and the science of culture had little to do with biology and that everything from human sex differences to aggression were purely cultural.

Yes, it made political sense for evo psych folks to rely more on data from physical anthro folks who approved of their work, and to neglect the data of the cultural anthro folks hostile to their work. But it doesn’t make scientific sense.

Yes, since human psychology evolved from the psychology of earlier primate ancestors, studying other primates can give us important clues about the origins of our psychology.  And yes, physical fossils like skulls give us clues to how our ancestors changed.  But cultural anthropologists have studied in great detail recent human societies that seem to have retained much of the lifestyle of our distant nomadic forager ancestors. Surely these contain powerful clues about the social environment in which human psychology evolved.

Which brings me to Christopher Boehm and his 1999 classic  Hierarchy in the Forest, a book that has greatly influenced my thinking over the last few months.  Boehm studied on both sides of the anthropology divide, working with both chimps and “primitive” humans.  He has fashioned a powerful synthesis. A few quotes:

As members of bands or tribes, humans can be quite egalitarian … Individuals who otherwise would be subordinated are clever enough to form a large and united political coalition. … Because the united subordinates are constantly putting down the more assertive alpha types in their midst, egalitarianism is in effect a bizarre type of political hierarchy: the weak combine forces to actively dominate the strong. … They must continue such domination if they are to remain autonomous and equal, and prehistorically we shall see that they appear to have done so very predictably as long as hunting bands remained mobile. … The egalitarian political lifestyle of Upper Paleolithic hunter-gatherers could have profoundly affected our evolving social nature.

The three African great apes, with whom we share this rather recent Common Ancestor, are notably hierarchical. … Starting about five thousand years ago … people were beginning to live increasingly in chiefdoms, societies with highly privileged individuals … But before twelve thousand years ago, humans basically were egalitarian.  They lived in what might be called societies of equals, with minimal political centralization and no social classes. Everyone participated in group decisions, and outside the family there were no dominators. For more than five millennia now, the human trend has been toward hierarchy rather than equality. But the past several centuries have witnessed sporadic but highly successful attempts to reverse this trend. …

Large-game hunting brings special reputational benefits. Large game is shared by the entire band, and the resulting prestige lends itself to political ascendancy.

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Homo Hypocritus

By Robin Hanson · March 23, 2010 9:00 am · Comments (75)

The standard social brain theory seems in conflict with standard anthropologist accounts of ancestral forager lifestyles.  Might “man the sly rule bender” resolve this conflict?

Why do we have ginormous brains?  Animals tend to have big brains when they have big bodies, but beyond that the main brain pattern is social: bigger brains are found in birds and mammals that compete with predators or prey, and who manage pair-bonding mate relations.  The extra costs of big brains is outweighed by benefits of not being out-witted by others.

Primates (and hyenas) hit on the trick of reusing pair-bonding skills to manage friendships in large social groups.  Primates have huge expensive brains, which are bigger in species with larger social groups, and these groups spend more of their time managing social relations.  Bigger groups better protect against predators, though the coalition politics of dominance gets more complex in bigger groups.

Primates not only manage relations and coalitions, but they also track the relations and coalitions of others.  They are adept at judging how to help their coalitions, and when to switch sides.  The top chimp is often not the strongest, but instead the one with the strongest coalition, which gets to dominate food and mating, and stay best protected from predators; chimp investments in big brains often pay off handsomely.

Humans have the biggest primate brains of all. Over the last two million years hominid brains grew more where climates were variable, but they grew most where population densities were high.  This suggests that human brains were also big mainly due to social pressures.  The “mating mind” sexual selection hypothesis seems at odds with this density effect, and with the more general fact that polygamous species tend to have smaller brains.  “Man the tool user” stories seem to confuse broad group gains with individual benefits – smaller brains seem sufficient for copying others’ tool skills.  But even if social pressures were key, which pressures exactly?

Isolated nomadic forager bands today are “fossils” with crucial clues about our distant ancestors.  Anthropologists who study them report that overt dominance is rare, and long distances make war rare (as 4 million year old fossils suggest). Foragers live in tight quarters and use language to express and enforce social norms on food sharing, non-violence, mating freedom, communal decision making, and norm enforcement.  Anger, bragging, giving orders, and anything remotely resembling dominance among men is punished by avoidance, exile, and death as required.  Human’s unusual hidden female fertility also limits male dominance temptations.

The puzzle here is that consistent enforcement of such norms seems to drastically reduce the payoff to expensive coalition-politics-savvy brains.  If you can’t collude to grab the food or the women, and everyone is treated fairly based on their contributions, why bother to be so clever?  Yes, some brain innovations were required to support language, and maybe they wouldn’t have occurred in a small brain, but after that innovation human brains could have shrunk (as perhaps with hobbits).  Why did humans keep huge expensive brains?

In a messy real world, social norms expressed in language typically have many iffy boundary cases and ambiguities.  How much of what sort of food of what quality offered how conveniently counts as food sharing?  How big a frown is a grimace?  Sex with how close a relative counts as incest?  And so on.  This wouldn’t matter if boundary cases were decided randomly, but that seems unlikely.  Instead big brain gains come five ways:

Unnormed – coalition politics on acts uncovered by norms.
Skirt – keep actions near but not over edge of violating norms.
Cover – politics of observers on if to report an act to others.
Frame – lawyer-like arguing on if acts violate social norms.
Conspire – form coalitions on how to publicly interpet iffy acts.

Most norms have meta-norms against consciously trying to evade them.  Self-deception should help here; foragers might sincerely believe they usually just do their job and “tell it like it is”, and then unconsciously try to act, selectively report and frame acts, and support interpretation coalitions, to their advantage.  Instead of “man the tool user”, we might be better understood as “man the sly rule bender.”

Gains to rule bending could be greatly reduced via social norms with very clear simple rules.  But humans seems to usually prefer complex and ambiguous rules that require “judgment” to apply.  For example, foragers often have complex incest rules, forbidding a much wider range of sex partners than is needed to prevent genetic problems.  And acts of sorcery are allowed to count as acts of aggression that violate social norms and must be punished, even without concrete evidence showing such acts.  Both complex broad incest rules and allowing sorcery complaints greatly increase the scope for gains to large rule-bending brains, and suggest that we tend to prefer to allow such scope.

The idea that the main reason we have huge brains is to hypocritically bend rules seems to me a dramatic change in how we think about human nature.  If true, it should change how we understand a great many things in psychology and social science.  I’ve been obsessing about his topic for weeks, and last Thursday I ran it past Robin Dunbar, famed for his contributions to the social brain account, and he said it was pretty close to his view on the subject, and he suggested the incest example.

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