Tag Archives: evolutionary psychology

Your cuisinart, a prehistory

A famous movie cut, from 2001: A Space Odyssey, transitions from a bone club, hurled aloft by an australopithecine 2.5 million years ago, to a spacecraft in the year 2001.


Arthur Clarke and Stanley Kubrick, coming up with the plot for the movie/book, were influenced by the popular author Robert Ardrey. In his book African Genesis, Ardrey casts human evolution as a version of the story of Cain and Abel, except in his version the peaceful vegetarians (robust australopithecines) get clobbered by the club-wielding meat-eaters (gracile australopithecines).

We were born of risen apes, not fallen angels, and the apes were armed killers besides. And so what shall we wonder at? Our murders and massacres and missiles, and our irreconcilable regiments?  Or our treaties whatever they may be worth; our symphonies however seldom they may be played; our peaceful acres, however frequently they may be converted into battlefields; our dreams however rarely they may be accomplished. The miracle of man is not how far he has sunk but how magnificently he has risen. We are known among the stars by our poems, not our corpses.

Ardrey, along with Konrad Lorenz and Desmond Morris, was much in vogue in the 1960s: Sam Peckinpah was another movie director influenced by him. The man could turn a phrase. Unfortunately his speculations on evolution and human behavior are probably not of enduring value: he had the misfortune to take up the topic too early to take on board the sociobiological revolution pioneered by William Hamilton, Robert Trivers, and George Williams, and popularized by E. O. Wilson and Richard Dawkins.

Ardrey may not have been off-base in thinking that weaponry and warfare have been an important motive force in human biological and social evolution (more on this later). But where early stone tools are concerned, a different segue, from Oldowan chopper to Cuisnart may be more appropriate.


Recent research argues that early hominins could have dramatically increased available food energy by pounding vegetables and chopping up meat into more digestible pieces. Tool use may have been an early step in our ancestors’ move to high energy diets. Meat-eating began to be important in human evolution around 2.6 million years ago. Somewhat later we see evidence that some hominins have lighter jaws and aren’t chewing as much. So to celebrate this early dietary revolution, here’s a recipe:

Steak Tartare

Place in a food processor fitted with the metal chopping blade:

1 ½ pounds lean beef (tenderloin, top round, or sirloin) cut into ½ inch cubes

Pulse until meat is coarsely ground, 7-10 seconds. Do not over-process. Remove meat to a chilled platter or individual plates and gently form into 6 individual mounds.

[Optional: Make a spoon shaped indentation on top of each mound and crack into each

1 egg yolk.]

Divide and arrange in small piles around each serving:

½ cup minced onions
½ cup minced shallots
½ cup minced fresh parsley
¼ cup minced drained capers
8-12 anchovies (optional)

Serve immediately and pass separately:

Fresh lemon juice
Worcestershire sauce
Dijon mustard
Hot pepper sauce
Freshly ground black pepper

From The Joy of Cooking 1997

Dead baby monkeys

There’s a dark side to being a primate. A few years back a review article summarized data on rates of lethal aggression in non-human animals. The figure below shows some of the results. Several clusters of especially violent species stand out in the figure, including primates (redder is more violent). Bats are pretty nice, though (too bad about all the viruses).

dead monkeys

Much of the lethal aggression in primates involves infanticide. Sarah Hrdy demonstrated back in the 1970s that infanticide occurs regularly in Hanuman langurs, monkeys in India. A male who takes over a group of females will systematically kill offspring sired by the previous male. If you think evolution is about the survival of the species, this is hard to explain. But it makes sense given the logic of the selfish gene. Females who lose an infant return more quickly to breeding again, and the father of the next infant is likely to be the killer of the previous one.

Primates may be particularly vulnerable to this grim logic, because they spend a long time as infants. Among primates, commonly,


That is to say that the time, L, a female spends lactating for an infant (during which she is unlikely to conceive), is usually greater than the time, G, she spends gestating an infant. This puts particular pressure on males to hurry things along by eliminating nursing infants fathered by other males.astyanax

Death of Astyanax

As a result, infanticide is relatively common among primates, and females under particularly strong pressure to find ways to avoid it. Hanuman langurs live in one-male units, where a female has little choice about who she mates with. In other species, by contrast (most baboons, chimpanzees), multiple males reside with multiple females. In these species females are often sexually promiscuous, sometimes actively soliciting multiple males for sex. This is probably mostly a matter of confusing paternity sufficiently to suppress the threat of infanticide. There’s a general lesson here: females are not always monogamously inclined, but female promiscuity generally has different evolutionary roots than male promiscuity.

Leaves of grass

70.3 – 66.6 million years ago

Not as dramatic as the evolution of Triceratops or T. rex, but of more lasting consequence, is the evolution of grasses (Poaceae). We know from coprolites – fossil feces — that grass was around by the Late Cretaceous, so the coevolution of grass and grazers had already begun with dinosaurs. These early grasses were not widespread. It would take climate shifts and more evolution (toward using carbon dioxide more efficiently) to create the sort of grasslands we are familiar with.

Grasses have played a central role in human evolution and human history. Human beings evolved in tropical grasslands, and some evolutionary psychologists think we still have an instinctive affinity for this environment. The domestication of grasses (wheat, barley, oats, millet, rice, corn) was one of the great revolutions in human prehistory, and grasses provided most of the calories people ate for most of recorded history. Contact along the frontier between grasslands supporting pastoralists and grain growing lands supporting peasants is one of the great engines of historical dynamics.

Grasses grow from the base of the leaf, not the tip of the stem, which is what allows them to recover from being grazed. This makes them a recurring symbol both of the transitoriness of life (“All flesh is grass, and all the goodliness thereof is like the flower of the field,” Isaiah 40:6) and its resilience.

Brahms used another verse about grass in the second movement of his German Requiem “For all flesh is as grass, and all the glory of man as the flower of grass. The grass withereth, and the flower thereof falleth away,” 1 Peter1:24. (Here is the German text and English translation.)

And the most famous poem about grass, by Walt Whitman, perhaps strikes the right elegiac note for the dinosaurs, who meet their doom tomorrow:

A child said, What is the grass? fetching it to me
with full hands;
How could I answer the child?. . . .I do not know what it
is any more than he.

I guess it must be the flag of my disposition, out of hopeful
green stuff woven.
Or I guess it is the handkerchief of the Lord,
A scented gift and remembrancer designedly dropped,
Bearing the owner’s name someway in the corners, that we
may see and remark, and say Whose?

Or I guess the grass is itself a child. . . .the produced babe
of the vegetation.

Or I guess it is a uniform hieroglyphic,
And it means, Sprouting alike in broad zones and narrow
Growing among black folks as among white,
Kanuck, Tuckahoe, Congressman, Cuff, I give them the
same, I receive them the same.

And now it seems to me the beautiful uncut hair of graves.
Tenderly will I use you curling grass,
It may be you transpire from the breasts of young men,
It may be if I had known them I would have loved them;
It may be you are from old people and from women, and
from offspring taken soon out of their mother’s laps,
And here you are the mother’s laps.

This grass is very dark to be from the white heads of old
Darker than the colorless beards of old men,
Dark to come from under the faint red roofs of mouths.

O I perceive after all so many uttering tongues!
And I perceive they do not come from the roofs of mouths
for nothing.

I wish I could translate the hints about the dead young men
and women,
And the hints about old men and mothers, and the offspring
taken soon out of their laps.

What do you think has become of the young and old men?
What do you think has become of the women and

They are alive and well somewhere;
The smallest sprouts show there is really no death,
And if ever there was it led forward life, and does not wait
at the end to arrest it,
And ceased the moment life appeared.

All goes onward and outward. . . .and nothing collapses,
And to die is different from what any one supposed, and

Europe of nations

September 1992 – April 1995

The 1991 disintegration of the Soviet Union was not widely anticipated. Academic Sovietologists were probably less likely than knowledgeable non-academics to anticipate that the Union was not going to last. One of the small number of people who got it right was public intellectual (and long-time Senator from New York) Daniel Patrick Moynihan. He argued a decade earlier that the Soviet system faced serious economic problems and that ethnic divisions were likely to lead to a collapse of the Union, as they had to earlier colonial empires like the British.

Being of Irish ancestry helped Moynihan to appreciate the continuing importance of ethnicity and nationalism under the cover of universalist ideologies. As warfare diminished in importance over the later twentieth century, the earlier Orwellian nightmare of a world divided into a few warring super-states receded, and an older vision of a Europe of nations revived. In 1900, neither Ireland, nor Poland, nor the Czech Republic was an independent country; by 2000 they were all running their own affairs – not because they built unstoppable military machines, but because they mobilized feelings of imagined community.

However there is a dark side to the return to nationalism. The newly independent nations of Eastern Europe were successful in resolving older border conflicts partly owing to a wave of mass killing and mass expulsions during and after the Second World War that tidied up the ethnic map. In Yugoslavia, where different nationalities were still heavily intermingled, the return to nationalism resulted in a civil war that killed about 130,000 people, and introduced the phrase “ethnic cleansing” to the language.

At the time, the fall of the Soviet Union and the Warsaw pact, and of communism is Eastern Europe, was widely seen as the decisive victory of one ideology – liberal capitalist democracy – over another. As it has turned out however, the fall of communism in Eastern Europe did not represent The End of History, even European history. Nationalism helped finish off the Soviet Empire; now it inspires both the defenders of Ukraine and Russian invaders.

On a scholarly note: Is ethnic nationalism an expression in the modern world of an evolved human psychology, a psychology shaped by the process of kin selection, as some scholars have argued? I considered the matter in an article, Kin selection and ethnic group selection (and here’s a blog post). The short answer: it’s complicated. Here’s my conclusion to the paper

Both the study of prehistory and political psychology are changing rapidly in the face of new evidence from biology, especially genetics. It would be intellectually satisfying if we could integrate these findings under the heading of an already existing theory, by equating ethnicity with kinship and applying kin selection theory. But we’ve seen that this won’t work. Ethnicity, like kinship, may have to do with shared genes. There may even be such a thing as ethnic nepotism. But an evolutionary theory of ethnicity – even the barebones theory presented here – has to be something more than the theory of kin selection, because of the way ethnicity is entangled with some of the most complicated aspects of human sociality: norms, rules, and political ideals, and their connection with large-scale population processes.

The modern synthesis and the blank slate

August 1941 – November 1946

We’re now dividing time finely enough to include months as well as years.

For most of the later nineteenth century after the publication of On the Origin of Species. biologists were skeptical of Darwin’s proposed mechanism of evolutionary change – natural selection. It was only in the twentieth century that this began to change. When Mendel’s work on heredity was rediscovered in 1900, it was originally seen by many as antithetical to Darwinism. But with the pioneering theoretical work of Fisher, Haldane, and Wright, and the subsequent empirical work of Mayr, Dobzhansky, Simpson, Huxley, Stebbins, and others, Darwin’s theory of natural selection and Mendel’s theory of heredity were combined in what came to be called “the modern synthesis.” Julian Huxley’s book Evolution: The Modern Synthesis marked the coming of age of the theory.

In an earlier post I noted how Lyell’s and Darwin’s embrace of gradualism in explaining the past (as well as George Eliot’s celebration of Dorothea Brooke’s “unhistoric acts” and “hidden life”) had something to do with the political climate in England in the years after the French Revolution and Napoleon. Evolution: The Modern Synthesis was first published in 1942. It’s no surprise that the modern synthesis too was a product of its time, when Nazi Germany and the Soviet Union offered gruesome antithetical demonstrations of how not to think about evolution, genes, and behavior.

Not coincidentally, at the same time that biologists in England and the United States were advancing the modern synthesis, social scientists – cultural anthropologists, behaviorist psychologists – were coming to embrace a strong blank slate view of human nature. (Carl Degler tells the American side of the story in In Search of Human Nature: The Decline and Revival of Darwinism in American Social Thought.) There grew up something amounting to a peace treaty between evolutionary biology and the social sciences, with the two fields agreeing to respect each others’ spheres of influence. Social scientists would leave biology to the biologists, accepting, for example, that neither a good upbringing nor acquired skills can improve your genes. Biologists in turn would largely steer clear of addressing social behavior. For example, the theory of sexual selection, which Darwin developed, and Fisher elaborated, was mostly dropped from the modern synthesis as it matured. Huxley argued (pretty unconvincingly in retrospect) that the elaborate mating dances and ornaments found in so many species were not a product of sexual selection, but merely helped to get individuals to choose the right species of mate. Westermarck’s pioneering work on the evolutionary psychology of incest avoidance and the incest taboo was largely shelved in favor of the shakier theories of Freud and Lévi-Strauss. Even Darwin’s work on emotional expression, which might have seemed fairly anodyne politically, was largely rejected by anthropologists. And the study of prehistory was affected as well.

It was only beginning in the 1960s and 1970s, with the rise of sociobiology, that evolutionary biologists returned to seriously addressing social behavior. Sociobiology: The New Synthesis (1975), by E. O Wilson, made a nod to Huxley in its subtitle. It also announced the end of an intellectual peace treaty, and the opening of an intellectual war that persists up to the present.

And here is my obituary for E. O. Wilson, who died last year.

The way and the word, continued

Continuing yesterday’s post: What accounts for the differences between classical Greek and early Chinese intellectual traditions? Below are a few things that might be involved; this is hardly a complete list.

Non-degenerate limit random variables

Here’s a nice little puzzle involving probability:

Take a bag with two marbles in it, one red and one green. Draw a marble at random. Put it back in the bag, and add another marble of the same color. Repeat: randomly draw one of the (now three) marbles in the bag, put it back, and again add a marble of the same color. Continue, adding a marble every time. What happens to the frequency of red marbles as the number of marbles in the bag goes to infinity?

Answer: When you carry out this procedure, the frequency approaches a limit. As the number of marbles grows larger, you sooner or later get, and stay, arbitrarily close to the limit. Now carry out the same infinite procedure a second time. This time you also approach a limit. But the limit this time is different! The first time, the limiting frequency might be .23748… . The second time it might be .93334… . If you keep on doing the infinite experiment a bunch of times, you’ll approach a different limit every time, with the various limits uniformly distributed over the interval [0,1]. These are non-degenerate limits. This is different from what you get when you flip a fair coin infinitely many times. The frequency of heads will always approach the same “degenerate” limit, .50000… .

A chance element like this is probably involved in the intellectual traditions of major civilizations. The first few great thinkers to come along have a massive influence on the direction of intellectual life, just as picking a red or green ball on the first round makes a big difference to the final limit. So Pythagoras’ and Plato’s obsessions with numbers and geometry as the keys to the universe have a disproportionate influence on later Western thought. Subsequent thinkers have progressively less and less influence, just as picking a green or red ball when there are already a hundred balls in the bag doesn’t make much difference in the ultimate limiting frequency.


But there may be more systematic things going on. Daniel Freedman was a psychologist, white, married to a Chinese-American woman. While awaiting the birth of their first child, the couple found that relatives on the two sides of the family had very different ideas about how newborns behave. Freedman was sufficiently intrigued that he carried out an investigation of assorted newborns in a San Francisco hospital, including babies of Chinese and European origin.

It was almost immediately apparent that Chinese and Caucasian babies were indeed like two different breeds. Caucasian babies started to cry more easily, and once started they were more difficult to console. Chinese babies adapted to almost any position in which they were placed.. … In a similar maneuver … we briefly pressed the baby’s nose with a cloth, forcing him to breathe with his mouth. Most Caucasian and black babies fight this … by immediately turning away or swiping at the cloth. However … the average Chinese baby in our study … simply lay on his back, breathing from his mouth. … Chinese babies were … more amenable and adaptable to the machinations of the examiners. p. 146

This might seem like a minor curiosity, but it fits neatly with later work demonstrating East-West differences in adult cognitive styles. This raises the possibility that differences in temperament evident at a very early age might influence the evolution of intellectual traditions.


Coined money apparently initially appeared in Lydia, in Asia Minor, around 600 BCE. It was quickly taken up by the Lydians’ Ionian Greek neighbors. And it is in Ionia too that we find the earliest philosophers. In Money and the Early Greek Mind, Richard Seaford argues that these developments are connected. The monetization of the Greek economy accustomed Greeks to the idea that a common impersonal material measure of value, relatively independent of individual control, underlay the multifarious goods and services produced by the polis economy. This led in turn to the pre-Socratic philosophers, who were obsessed with finding the one impersonal natural element – water, air, number – of which the whole heterogeneous variety of the natural world was made.

In Athens, the expansion of a monetary economy led to a curious insult – opsophagos, or fish-eater. What made this an insult is that fish were sold in the marketplace. They were a mere commodity, free of the ritual and taboos that surrounded the sacrifice and distribution of animal flesh. The fish-eater was a rich man indulging the pleasures of consumption free from the constraints of tradition and decorum. And his conspicuous consumption offended not only tradition but the spirit of democracy. Better that he spend his wealth on the public good.

In traditional China, by contrast, coins, and later paper money, would challenge but never break the hold of state patriarchy. And Spartans too recognized the subversive potential of money. Sparta used iron bars for money, precisely because they were inconvenient.

Achilles slash Patroclus

“Slash fiction” has nothing to do with slashers or serial killers. It’s a genre of fan fiction, depicting romances between male characters. The “slash” is a  “/”. For example, a Kirk / Spock story will be about Kirk and Spock coming to realize that they are more than just friends, and consummating a sexual relationship. Interestingly, the writers and readers of slash fiction are overwhelmingly female; it’s of little interest to gay men. And slash fiction follows the conventions of heterosexual romance novels. One of the characters, although biologically male, will be more female in psychology ­– more intuitive and emotional ­– and women readers will identify with him. (In Kirk / Spock stories, Kirk is usually the more feminine character, and Spock – aloof, logical – the more masculine). The sex in slash fiction is not sex-for-the-sake-of-sex, but sex as the expression of a monogamous emotional bond. (For a discussion of slash fiction from the perspective of evolutionary psychology, see Warrior Lovers: Erotic Fiction, Evolution, and Female Sexuality.)

The Song of Achilles, by Madeline Miller is an engaging best-selling retelling of the story of the Iliad with the relationship between Achilles and Patroclus at its center. Although neither the author or most reviewers seem to be aware of it, it very much fits the model of slash fiction, with Patroclus as the woman-in-a-man’s-body character, and Achilles as much more of a sensitive guy than the raging tragic hero of the Iliad. Miller is not the first historical novelist to bring this sensibility to a tale of the classical world. The Persian Boy, by Mary Renault (about Alexander the Great and the Persian eunuch Bagoas) and The Memoirs of Hadrian, by Marguerite Yourcenar (about Roman emperor Hadrian and Antinous) are two more examples. (Renault and Yourcenar were lesbians, Miller isn’t.)

Slash fiction testifies to the power of imagination, with readers and writers imagining their counterparts with very different bodies. But it also testifies to deep sex differences in sexuality. The counterpart to slash fiction for heterosexual men is the very different genre of hot girl-on-girl pornography, which is more revealing about male sexuality than about real-life lesbianism.

The Goodness Paradox

205 – 195 thousand years ago

We’re now doing history at ten thousand years a day.

Earth Abides is an early (1949) entry in the genre of post-apocalyptic science fiction, with some haunting reflections on what it takes to keep a civilization going, or just a human community. In this case the apocalypse takes the form of a lethal infectious disease that wipes out well over 99% of Earth’s human population, leaving scattered survivors to try and put things back together.

The drama is low-key. If you want to read about the remnants of civilized humanity defending themselves against zombies, or venomous man-eating walking plants, or a horde of cannibal anti-nuke zealots, you’ll have to look elsewhere. The threat to civilization in Earth Abides is more subtle. The generation born after the die-off has no understanding of what they have lost, of what the collapsing factories and powerlines and machines around them really were, or how they worked, or how to get them back up and running. The older generation, without the institutions of a complex society backing them up, can’t supply enough discipline and punishment to pass on the arts of civilization. The young will grow up as illiterate scavenger-foragers, skilled with bow and arrow, well-adapted in their own way to a rewilding Earth. Ish, the protagonist, will end his days as the Last American (a fictional counterpoint to the real-life Ishi, the last Yahi Indian).

The community is nonetheless capable of reacting decisively when their survival is threatened.

One day a newcomer enters the scene. Charlie is talkative, forceful, charismatic. The kids adore him. It looks like he might even take over as leader of the little group. But it becomes clear that there is something off about him, even sociopathic. He can turn on the charm, but when thwarted he is menacing. He always carries a gun, which he keeps hidden. He is sexually abandoned. And, in a world without antibiotics, he is infected with a slew of venereal diseases.

Something has to be done about Charlie, and the elders of the group meet to decide what. Their options are limited. Keeping him locked up is not a practical possibility for this tiny community. They could banish him. But who is to say he won’t find a gun, and come back, looking for revenge? They could execute him. But what actual harm has he done, so far? They decide to settle the matter with a vote.

Em located four pencils. Ish tore a sheet of paper into four small ballots.

This we do, not hastily; this we do, not in passion; this we do, without hatred. …

This is the one who killed his fellow unprovoked; this is the one who stole the child away; this is the one who spat upon the image of our God; this is the one who leagued himself with the Devil to be a witch; this is the one who corrupted our youth; this is the one who told the enemy of our secret places.

We are afraid but we do not talk of fear. … We say, “Justice”; we say, “The Law”; we say “We, the people”; we say, “The State.”

Ish sat with his pencil poised … He could not be sure. Yet, at the same time, he knew that The Tribe faced something real and dangerous and even dreadful, in the long run threatening its very existence. … In that final realization, he knew that he could write only the one word there, out of love and responsibility for his children and grandchildren. …

“Give me your slips,” he said.

They passed them in, and he laid them face up before him on the desk. Four times he looked, and he read: “Death … death … death … death.”

Keith Otterbein is an anthropologist who did a study of capital punishment across cultures. He expected to find that capital punishment is limited to complex societies, used to enforce social hierarchy. Instead he found that capital punishment is a universal, present in societies from the simplest to the most complex. It is an option that even the smallest, most easy-going communities – like The Tribe of Earth Abides – may find themselves resorting to. We can infer that for tens or even hundreds of thousands of years, our ancestors have been carrying out group-sanctioned executions of individuals deemed anti-social and a threat to group harmony and survival. This is long enough to have had evolutionary consequences. Long before we domesticated the wolf, the wild sheep and goat, the aurochs, we may have been domesticating ourselves, weeding out the wildest and most dangerous from our midst, replacing the old tyranny of the alpha male with the new tyranny of Custom and The Law.

The idea that human beings are in some ways like domesticated animals is an old one. It has recently returned to the spotlight. The extraordinary long-term experiment in artificial selection for tameness in foxes carried out by Nikolai Belyaev, Lyudmila Trut, and their coworkers in Russia has demonstrated that selection for tameness ends up selecting for a whole suite of anatomical characteristics as byproducts. Strikingly, many of the features that differentiate Homo sapiens hundreds of thousands of years ago from Homo sapiens today are also features that distinguish tame from wild foxes, and dogs from wolves.

Richard Wrangham’s recent book, The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution connects the dots, setting out one long argument that an evolutionary history of capital punishment has reduced our disposition for reactive aggression (the hot-blooded, spur-of-the-moment, volatile, antisocial kind), while leaving intact our capacity for calculated, cold-blooded, proactive killing (“not hastily, … not in passion, … without hatred”).

Perhaps this explains a very recent finding in human evolution. Apparently 200,000 years ago, we were about evenly matched with Neanderthals, sometimes replacing them, sometimes being replaced by them. By 40,000 years ago however, Neanderthals lose out decisively to modern humans. It may be that what changed in the interim to give us the edge is that we improved our ability to get along peaceably with insiders (including distant insiders we don’t know personally) without losing our ability to apply lethal aggression to outsiders.

It’s a small world after all

The story of human origins is partly a story of Big Things like The Taming of Fire and  The Dawn of Speech. But it’s also the story of some odd byways and quiddities. A nice introduction to some of these is Chip Walter’s book Thumbs, Toes, and Tears: And Other Traits That Make Us Human. (His more recent Last Ape Standing is good too.) Walters considers funny bits of anatomy like our unique big toes and thumbs, and funny bits of behavior like our habits of laughing, weeping, and kissing. Toes and thumbs fossilize, but behaviors can be hard to date, evolutionarily. Presumably these behaviors appeared sometime before modern humans evolved and spread, so let’s pick today’s date. It’s also hard to figure out the exact evolutionary rationale for some of these behaviors. Humor, for example, is not a simple phenomenon: intellectually appreciating a joke, actually finding it funny and enjoying it, and finally laughing, each involve separate areas of the brain.

Laughter, specifically, is a minor human oddity that sheds an interesting light on some big events in human evolution. Robert Provine, a leading laughter researcher, spells out the argument in “Curious Behavior: Yawning, Laughing, Hiccuping, and Beyond.” Chimpanzees have a kind of laugh, a modified vocalized panting synchronized with inhalation and exhalation. Presumably laughter first resulted when panting-during-play evolved into a play signal. But the short bursts of human laughter go further, having freed themselves from synchrony with the inhalation/exhalation cycle. Laughter, in other words, is just one instance of the more general phenomenon of humans having separate controls for vocalization and for respiration. Interestingly, the most prominent examples of complex vocalization – songbirds and some other birds, whales, bats, and humans – are all found in non-quadrupeds. In quadrupeds, breathing is tightly coupled with locomotion: lungs need to be full to stiffen the thorax when the forelimbs hit the ground. Giving up quadrupedalism seems to have allowed for an “adaptive release” in the evolution of vocal abilities in a number of unrelated lineages. So the study of laughter (and other vocalizations) suggests that two key human adaptations – bipedalism and spoken language – are more closely linked than one might have expected.

Another and overlapping set of human particularities involves facial expressions of the emotions. Darwin got a whole book out of this. He concluded (admittedly based on somewhat anecdotal evidence) that different emotional expressions are largely innate. It’s an interesting illustration of his ability to reason from small facts to large conclusions that he also drew a big conclusion about human evolution from this. In Darwin’s day, there were scientists who believed that different human races had evolved from very different prehuman progenitors: one prehuman species giving rise to Europeans, another to Africans, and so on. But Darwin reasoned that the very close similarity in facial expressions (and he had traveled a lot, and witnessed a lot of expressions in a lot of places) and the very similar emotional makeup of humans around the world was evidence that human populations shared a fairly recent common ancestry. Here as in several other cases, a mixture of close reasoning and sheer luck led Darwin to the correct conclusion about evolution long before there was much solid evidence.

Darwin’s work on emotions was neglected for most of the twentieth century by anthropologists favoring a blank slate view of human behavior, but was eventually largely vindicated by a number of researchers, notably Paul Ekman. There is now good evidence for six basic facially expressed emotions: Fear, Disgust, Joy, Anger, Sadness, and Surprise.

If you’re a movie watcher, this list may seem familiar. These emotions (all except for Surprise) are all depicted as little homunculi living inside the head of an 11 year old girl in the animated feature “Inside Out.” Somebody at Pixar Studios knows their Ekman.


So the sappy song is right: There is just one moon and one golden sun, and a smile means friendship to everyone.

Calories and curves

1.38 -1.32 million years ago


This figure is from a neat recent paper comparing energy expenditure (TEE or Total Energy Expended) and fat among humans and our closest relations: chimpanzees (genus Pan), gorillas (Gorilla), and orangutans (Pongo). (The numbers are adjusted for differences in overall body mass.)

What stands out here is that humans are a high energy species. Also we carry a lot more body fat than the other great apes. This applies particularly to women, who need a lot of extra fat to meet the high energy demands of human infants. But it even applies to men. For both sexes, a high energy life style means you want to carry around an extra reserve of fat in case of emergencies.

We don’t know how long ago our ancestors decided to crank up their energy consumption. Maybe back with the rise of Homo erectus (just a few days ago on Logarithmic History). Or maybe later, when the typical modern human pattern of slow maturation was more firmly in place. At some point in the near future, we’ll actually nail down the specific genetic changes leading humans to accumulate more fat, and be able to put a date on the change. It may be that the distinctively human mating system also arose back then, with human females concealing ovulation (no chimp-style monthly sexual swellings) but advertising nubility (with conspicuous fat deposits appearing at puberty)

A high energy life-style also goes with extensive food sharing and changes in human kinship. (Here’s me, on beating Hamilton’s rule through socially enforced nepotism.)