Tag Archives: evolutionary psychology

Physical attractiveness and the theory of sexual selection

As we wait for our solar system to appear (coming up soon, January 20), here again is a break in the proper order of things on Logarithmic History, introducing some of my own work, in this case a pdf of a book from a while back. The book, Physical Attractiveness and the Theory of Sexual Selection: Results from Five Populations (1996), based on my PhD thesis and several articles, presents results of research on standards of physical attractiveness in five populations: Americans, Brazilians, Russians, Ache Indians (Paraguay) and Hiwi Indians (Venezuela). (Data for the Hiwi were collected by my adviser Kim Hill).

Looking back, I would say that the book, and the associated research, was a pioneering effort. When it came out there was already a significant body of work in social psychology on criteria and consequences of attractiveness. But the research in the book was some of the first to get truly cross-cultural, including data from isolated former hunter-gatherers. And it was some of the earliest work on attractiveness to try and connect the psychology literature with the theory of sexual selection, and with research on sexual selection in non-humans.

There are things I would change if I were doing a rewrite. There are occasional plain mistakes – minor mistranslations, and so on. And the statistical analysis could be improved on. For example, when it comes to the data on race and somatic prejudice in Brazil, I do a better analysis in this book chapter.

In the main however, the book holds up fairly well. There’s a lot of concern in the human sciences these days about whether research results are replicable and reliable. From this perspective it’s reassuring that some major findings of the book – that men find especially feminine/neotenous women’s faces especially attractive, that faces closer to the population average are seen as more attractive – are supported by later research. (On the flip side, I was one of the first people to look for a connection between fluctuating asymmetry and attractiveness in any species. I found no significant correlation.)

On a philosophical note: on December 18 last year, I reposted some reflections on the evolution of human sexuality. The Schopenhauer quotation from that post (my translation) first appeared in Physical Attractiveness and the Theory of Sexual Selection, a book in which “I have striven not to laugh at human actions, not to weep at them, nor to hate them, but to understand them” (Baruch Spinoza).


Kin selection and ethnic group selection

Sometimes I interrupt the normal day-by-day progression of Logarithmic History to cover my own work. Here I introduce a just-published paper, “Kin selection and ethnic group selection.” It’s about what, if anything, ethnicity has in common with kinship – evolutionarily speaking that is, on the assumption that human psychology has been shaped by natural selection. The paper doesn’t have anything to do with galaxy formation or nucleosynthesis, recent topics on the blog, but it would have been a good fit on August 5 last year, when I wrote about cultural group selection, population genetics, and prehistory, or December 15, when I wrote about nationalism in Europe at the end of the Cold War.

The paper itself is behind a paywall, but here’s a link to an earlier uncorrected, unpublished draft.

As a starting point, take the concept of ethnic nepotism. If you look up the term on the web, one thing you’ll find is an array of sources arguing that ethnicity is kinship on a large scale, and that the theory of kin selection, developed in evolutionary biology to explain altruism, cooperation, and conflict in families, is also a key to understanding such things at the level of ethnic groups. In the paper, I cite academic publications that take this position, including some from my late colleague at the University of Utah, Henry Harpending. And here is a non-academic link.

But you’ll also find people arguing the opposite, that ethnicity can’t be equated with kinship, at least as far as the theory of kin selection is concerned. Again I cite academic publications in the paper, and here, here, and here are some non-academic links.

The nay-sayers win the first round of the argument. I cover this in the first part of the paper. The theory of kin selection is concerned with r, the coefficient of relatedness, the expected number of genes that one organism shares with another as a result of common descent. Natural selection favors altruism between family members in proportion to their r’s, as a gene’s way of making more genes. So we’re told by William Hamilton, the biologist who figured this out. As it turns out, we can calculate r values not just for families, but for large groups – nations, continent-scale races. Does this mean we can plug these r’s into the standard formula and predict altruism between ethnic group members accordingly? No, because we’re now violating something called the weak selection assumption (see the paper for details). A physics analogy: at Earth’s surface, a falling object accelerates at a constant 9.8 meters per second per second. So we’re told by Galileo. This works for heavy objects over short distances. But we run into problems if we try to apply this law to lighter objects and longer distances without allowing for air resistance. Assuming weak selection in the theory of kin selection is like assuming no air resistance in physics, a simplifying assumption that can get us in trouble.

Eppur … even if ethnicity can’t simply be equated with kinship, it’s still theoretically possible to rescue the idea of ethnic nepotism, with the help of two further principles.

Socially enforced altruism. Suppose you decide, on your own, to help somebody at some cost to yourself. (If we’re thinking about evolution, we’ll want to count benefits and costs as fitness increments and decrements.) This is an instance of individual altruism. Discussions of kin selection commonly begin and often end here. But now imagine that you are part of a group that decides collectively to help another group. You and your fellow villagers, say, vote to tax yourselves to help a neighboring village recover from a flood; you don’t expect them to pay you back. This is socially enforced altruism. It’s not altruism at the individual level – you pay the tax to avoid a penalty – but it’s altruism at the village level – y’all could have kept the money for yourselves. In an earlier paper, I analyzed a variant on this, a reputation-based system where you help the needy not so much out of pure kindness, but to get the benefits that go with having a good reputation. I showed how the social enforcement of charity via reputation can amplify altruism toward distant kin. (Here’s the article, and a blog post about it, Beating Hamilton’s Rule, and an earlier article, Group nepotism and human kinship, and another post on the Brothers Karamazov Game, a simple three-person version of group nepotism.)

Ethnic group relatedness. The earlier paper was concerned with socially enforced altruism at the scale of local kin groups. Socially enforced altruism might also work at the level of ethnic groups. In this case, however, genetic similarity among segments of an ethnic group may reflect something other than just shared descent. In this case, two segments of an ethnic group may be genetically similar because they have shared a common culture for some time, resulting in similar selection pressures on genes contributing to the maintenance of that cultural regime. The basic principle behind kin selection can still operate here – you (or y’all; see above) help others because they share your genes, even if they can’t pay you back. But the expected number of shared genes – the ethnic coefficient of relatedness – no longer tracks the standard r’s based on genealogy or genetic similarity over the genome as a whole.

So ethnic group nepotism resulting from ethnic group selection* is a theoretical possibility, and I lay out the theory in the middle part of the paper. Whether it actually occurs I consider in the last part of the paper, which reviews some population genetics and political psychology.**


* Depending on how we define our terms, selection for socially enforced altruism may or may not count as group selection, but either way the usual objections to group selection for pure altruism don’t hold here.

** The social science literature on ethnicity and nationalism, including Conor, Gat, and Horowitz, is a topic for another day.

We are MacApes, O’Monkeys, and Ben-Reptiles


A couple years back, Jonathan Marx and Jerry Coyne had an online spat on the question “Are humans apes?” (Marx says noCoyne says yes; see also John Hawks, who says no.) I offer my own solution below, after talking about Linnaeus (1707-1778) and biological categorization.

There’s a branch of cultural anthropology that studies “folk biology,” also known as “ethnobiology,” which is (among other things) about how different groups classify living things. Folk biological categories don’t vary randomly across cultures; there are some general principles at work. A quick summary: the basic level of categorization is roughly the genus. American folk genera include oakcrow, and fox (although a lot of Americans today are really bad at folk biology, maybe using that part of the brain for Pokemon.) Many peoples, and most hunter-gatherers, only take categorization down to the genus level. Others (especially horticulturalists) take it down to the species level, often with two part names (red oak, silver fox). Going toward more inclusive groups, genera are lumped together in larger, intermediate-sized, non-overlapping categories (palmhawk), which belong in turn to the more inclusive level of “life forms”: (bird, snake, fish, tree, grass/herb).

From an anthropological perspective, Linnaeus’s famous scheme of classification is an elaboration of these universal principles, with more species and more taxonomic levels (the famous Kingdom, Phylum, Class, Order, Family, Genus, Species).

A version of Linnaeus’s scheme served evolutionary biologist well for centuries. But starting in the later twentieth century, many biologists turned to another approach that was claimed to be a better fit for evolutionary principles: According to cladists, the classification of living things should be based on clades: groups containing all and only the descendants of an ancestor. This requires overturning or revising many familiar categories. For example, monkeys are not a clade, since Old World monkeys are more closely related to apes (including humans) than to New World monkeys. Reptiles are not a clade, since crocodiles are more closely related to birds than to lizards and snakes. Fish are not a clade, since lungfish are more closely related to amphibians and reptiles than to most other fish.

After some bitter disputes. cladists seems to have won the battle among scientists. But cladism has made less headway among non-scientists. In Naming Nature: The Clash Between Instinct and Science, Carol Yoon argues that cladistics is just too much at variance with the way the human mind understands biological categories. Most people are never going to take to cladistics any more than they’re going to take to twelve-tone music, or Loglan. So different answers to the question “Are humans apes?” reflect disagreement about how far we can or should bring folk categories in line with the austere logic of cladism. Apes, including humans, are a clade. Apes, not including humans, are not (since chimpanzees are more closely related – but not really more similar – to humans than to gorillas).

I suggest a compromise. Folk categories like ape, monkey, reptile, and fish, defined by shared ancestral traits, are useful, even if they aren’t clades, defined by shared derived traits. But the concept of a clade is also important one for biologists. So maybe when we want to talk about the clades associated with folk categories, why don’t we use a prefix – the Scottish Mac, Irish O’, or Hebrew/Arabic ben/bin. (Any of these will serve.) So human beings are not apes, monkeys, reptiles, or fish. But we are MacApes, O’Monkeys, Ben Reptiles, and/or Bin Fish.

(For other We Are posts see We Are Upside Down Bugs and We are Stardust.)

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. Boyd and Richerson 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!

592-560 thousand years ago

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 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’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.” (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.

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?

Ardrey, along with Konrad Lorenz and Desmond Morris, was much in vogue in the 1960s: Sam Peckinpah was another movie director influenced by him. 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. 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