Tag Archives: evolutionary psychology

Dead baby monkeys

There’s a dark side to being a primate. Last year 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.

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. Commonly L/G>1, that is to say, 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.

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: female promiscuity generally has different evolutionary roots than male promiscuity.

Leaves of grass

Not as dramatic as the evolution of Triceratops, Tarchea giganta, 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.

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

“My nights were sour, spent with Schopenhauer.” (G. Gershwin)

1998. Bill Clinton is impeached by the House of Representatives, only the second US President to be impeached, after Andrew Johnson in 1868. The charges are perjury and obstruction of justice. Clinton has a long record of philandering going back to his days as governor of Arkansas and continuing to the White House. His attempts to cover this up give Republicans in the House an opening for impeachment. Clinton also pays a $90,000 fine for lying about his relations with Paula Jones, an Arkansan who accused him of sexual harassment. He eventually settles out of court with Jones for $850,000.

In 2000, the Presidential campaign of Al Gore keeps its distance from Clinton. In polls, an exceptionally high percentage of potential voters list “moral character” as an important issue in the election, and these voters mostly favor Gore’s opponent, George W. Bush. Gore believes that the Clinton scandals cost him the election.

Here’s a quote from the great pessimistic philosopher Schopenhauer:

Sexual love … next to the love of life … shows itself as the strongest and most active of motives, and constantly lays claim to half the powers and thoughts of the younger portion of mankind. It is the ultimate goal of almost all human effort. It exerts an unfavorable influence on the most important affairs, interrupts every hour the most serious occupations, and sometimes confuses for a while even the greatest minds. It does not hesitate to intrude with its trash, interfering with the negotiations of statesmen and the investigations of the learned … It devises daily the most entangled and the worst actions, destroys the most valuable relationships, breaks the strongest bonds, demands the sacrifice sometimes of life or health, sometimes of wealth, rank and happiness. Indeed, it destroys the conscience of the otherwise honest, makes traitors of the once loyal … One is forced to cry: Why all this noise? Why the strain, turmoil worry and effort? … Why should such a trifle pay so important a part, and constantly introduce disturbance and confusion into the well-regulated life of man? But to the earnest investigator the spirit of truth gradually reveals the answer: it is no trifle that is in question here; on the contrary, the importance of the matter is quite proportionate to the seriousness and ardor of the effort. The ultimate aim of all love affairs … is actually more important than all other aims in human life, and is therefore quite worthy of the profound seriousness with which everyone pursues it. What is decided by it is nothing less than the composition of the next generation … This is the key to the problem.

Schopenhauer actually anticipated a lot of Darwin’s theory of sexual selection – for example, how differences in men’s and women’s sexuality derive from differences in potential rates of reproduction. However he got there with the help of a lot of high-flown Germanic idealist talk about the Will to Live, rather than with scientific arguments.

Schopenhauer’s greatest disciple is Richard Wagner. If most of Mozart’s operas are about the triumph of monogamy in the face of obstacles, then most of Wagner’s operas are about the destructive antisocial nature of sexual love.

Europe of nations

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 Irish by 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 was 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.

On a scholarly note:

The theory of comparative advantage, in economics, and the theory of kin selection, in evolutionary biology, are two of the great theories in the social sciences. But both theories, in their usual elementary form, depend on some simplifying assumptions. You can get in trouble if you apply either theory carelessly without noticing if those assumptions are violated.

When it comes to winners and losers in international trade, I’ve already noted some complications. What’s of note where this post is concerned: some people have tried to apply the theory of kin selection to explain ethnicity and ethnocentrism as expressions of ethnic nepotism. But converting coefficients of inbreeding into coefficients of relatedness among kin is a dicey business. I’ve had more to say about the topic in a couple of articles, and a blogpost, and will have more to say in the future. Stay tuned!

Learn This One Weird Trick … (Part One)

… that humans use, and now you can too!

There are people who think that human beings are nothing special. Sure (the argument goes) people have uniquely large brains. But all sorts of creatures have unique features. Elephants are the only animals with trunks. Tamarins and marmosets are the only primates that give birth to twins. Platypuses are the only venomous mammals. Spotted hyenas are the only mammals whose females sport pseudo-penises (through which they give birth!). And so on. If we could ask members of these species they’d claim that they’re the special ones.

But of course we can’t ask them, and in any case, this isn’t a very convincing argument. Human beings have an absolutely outsize impact on the Earth, and the advent of human beings looks like one of the major evolutionary transitions, comparable in importance to the origin of the eukaryotic cell or multicellular life. But even if we buy this, it still leaves open the question of whether there’s a key adaptation – a One Weird Trick – that accounts for the exceptional course of human evolution. Here are some candidates that being are being batted around these days:

1) The cognitive niche. The basic idea is at least as old as Aristotle, that human brings are defined by their capacity for Reason. A modern version of this is advocated by evolutionary psychologist John Tooby and cognitive scientist Steven Pinker. Pinker in particular has elaborated the argument that humans are uniquely adapted to acquire and share knowledge, by virtue of a suite of cognitive, social, and linguistic adaptations. We’ve already touched on several aspects of this: Human beings seem to have taken the capacity for thinking about physical space and retooled it for thinking about the abstract cognitive space of possession – a social relationship. (Other abstract cognitive spaces include kinship, time, and change-of-state.) And humans seem to harness the machinery for processing the sounds of interacting solid objects in creating major categories of phonemes. For a more complete exposition, here’s an academic article by Pinker, and a talk on youtube.

2) Culture. Rob Boyd and Pete Richerson, who’ve done a lot of mathematical modeling of cultural evolution, are skeptical about the “cognitive niche” argument. Too much culture, they argue, is things that have been learned by trial-and-error, and are passed on from one generation to the next without people understanding why they work. They appeal, as anthropologists have for generations, to the importance of culture. We mentioned earlier their argument that the frequency of climate change in the Ice Age was nicely calibrated to favor social learning rather than individual learning or instinct. Joseph Henrich provides a recent defense of the importance of culture. Contra Pinker, he thinks humans often don’t have a good cause-and-effect understanding of the things they do, but depend heavily on imitation and the accumulated wisdom of the elders.

Coming up: Part Two. Recursion and Shared Intentionality

Hits, slides, and rings

Part of the challenge of language is coming up with some way to distinguish thousands or tens of thousands of words from one another. It would be hard to come up with that many unique sounds. What human languages do instead is to come up with phonemes and rules for stringing phonemes together into syllables, and then create words by arbitrarily pairing up one syllable, or a few, with a meaning. Phonemes are the individual sounds of a language, roughly comparable to individual letters. There are about forty phonemes in most dialects of English. (English spelling does a pretty sloppy job of matching up phonemes and letters. Finnish comes close to one phoneme per letter.)

Often in evolution organisms don’t solve new problems from scratch, but instead harness preexisting adaptations. I argued earlier that the abstract “space” of possession (“The Crampden estate went to Reginald.”) may have developed by harnessing preexisting concepts of physical space. And our abilities to recognize speech sounds may harness our preexisting capacities for recognizing the sounds of solid objects interacting. At least that’s the argument of a recent book by Mark Changizi, Harnessed: How Language and Music Mimicked Nature and Transformed Ape to Man.

Changizi notes that even though we’re mostly not aware of it, we’re very good at using our hearing to keep track of what’s going on in our physical surroundings. For example, people easily recognize the difference between someone going upstairs and someone going downstairs, and we’re pretty good at recognizing individuals by their treads. The sounds that solid objects make can be broadly categorized as hits, slides, and rings. Hits: one object collides with another and sends out a sharp burst of sound. Slides: an object scrapes against another and sends out a more extended sound. Rings: an object reverberates after a collision. Changizi argues that these correspond to the major categories of phonemes.

  • Hits = plosives, like p b t g k
  • Slides = fricatives, like s sh th f v z
  • Rings = sonorants, including sonorant consonants, like l r y w m n, and vowels

These are not the only sounds we can make with our mouths. We can do barks and pops and farts and so on. But our auditory systems are especially cued into solid object physics, so when we try to come up with easy-to-distinguish phonemes, that’s what we focus on. And a lot of rules about how phonemes hook up also follow from this principle – for example hits followed by rings are more common than the reverse.

There’s surely more going on with speech sounds than Changizi allows for. But if imitating nature is not the whole story of phonemes, it may at least be where they got started.

Later on when we talk about writing systems, we’ll see there’s a similar argument about how these are tuned to tickle our primate visual systems.

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. (We’ll have more to say about language origins soon.) 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 it can be hard to put dates on when behaviors evolved. Presumably it was sometime before modern humans evolved and spread, so let’s make it today’s date, 570-547 thousand years ago. It’s also hard to figure out the exact evolutionary rationale for 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.

Another and overlapping set of human particularities involve facial expressions of the emotions. Darwin got a whole book out of this. He concluded (admittedly based on somewhat anecdotal methods) 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 made it to the movies last summer, 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.” (The movie gets a strong thumbs up from Logarithmic History). 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.