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).


Evolution and broken symmetries

8.33-7.88 billion years ago.

No big news in the universe today. Some evolutionary thoughts: Species evolve. Do planets? stars? galaxies?

Charles Darwin didn’t use the word “evolution” often. But he did write a lot about “descent with modification,” which is pretty much what biologists mean by evolution. For example, the usual definition of genetic evolution is “change in gene frequency,” i.e. descent with (genetic) modification.

However, people sometimes talk about evolution that doesn’t involve descent with modification, in contexts that have nothing much to do with biological evolution – cosmic evolution or stellar evolution in the history of the universe, for example, or mineral evolution in the history of the earth. Another Victorian writer, the sociologist and philosopher Herbert Spencer, offered a definition of evolution that might cover these cases.

Evolution is an integration of matter and concomitant dissipation of motion; during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity.

It’s easy to make fun of this definition. It’s the sort of abstract word pile that style manuals tell you to avoid, and that gives sociology a bad name. For that matter, it’s easy to make fun of Herbert Spencer. He may be some of the inspiration for the character of Mr. Casaubon, the dried up, impotent pedant in George Eliot’s “Middlemarch.” (Spencer probably turned down a chance to marry George Eliot = Mary Ann Evans. You should be careful about offending a writer.) But it may be that Spencer was groping toward the important modern concepts of symmetry and symmetry breaking.

A simple example: imagine you’re holding a bicycle exactly upright. The bicycle is pretty much bilaterally (mirror image) symmetrical. (OK, not really, the gears are on the right side, so it’s not a perfect mirror image. But just pretend …) Now let go of the bike. It will fall to one side or the other. The symmetry is broken, and you need one extra “bit” of information to tell you which side the bicycle is on.

Symmetry breaking is a fundamental concept in physics. In the very early history of the universe, the four forces of nature — gravitational, strong, weak, and electromagnetic – were united, but then as the universe cooled, one by one, these forces broke the symmetry and turned into separate forces. More symmetry breaking generated elementary particles, and nuclei, and atoms. When atoms first formed, they were distributed symmetrically through the universe as a diffuse gas. But gravitation pulled atoms and other particles together into clumps, leaving other parts of space emptier, and the spatial symmetry was broken (a “translational” symmetry in this case).

Symmetry breaking will keep showing up throughout the history of the universe. Consider sexual reproduction. A simple early form of sex involved two equal sized gametes (sex cells) joining to produce a new organism. Some species still do it this way. But more commonly the symmetry is broken – some organs or organisms produce little gametes that move around easily (sperm or pollen), others produce big gametes that don’t move around so easily (eggs or ovules). We call the first sort of organs or organisms male and the second sort female. Sex in most multi-cellular organisms is a broken symmetry. This broken symmetry will go on to have a dramatic consequences for human social evolution. It entails, for example, that patrilineages can expand their size much more rapidly than matrilineages.

Or consider the rise of political stratification, the move from small-scale societies where “every man is a chief” to large-scale societies of chiefs and commoners, rulers and ruled. Another broken symmetry. It may be more or less an accident (good or bad luck, Game of Thrones style) who ends up being king, but it’s not an accident that somebody is, past a certain social scale.

We don’t attach much moral significance to broken symmetries where the physical world is concerned. You’re being way too sensitive if you feel sorry for the poor weak nuclear force that missed its chance to be the strong nuclear force, or for the dwarf galaxies that got cruelly tossed around and cannibalized by the Milky Way. Broken symmetries in social life – males and females, kings and commoners – are another matter …

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.

The curve of binding energy

More stardust

Looking at the abundance of different elements in the universe, we get the following:

element abundances

Note that the vertical scale is logarithmic, so there is vastly more hydrogen and helium in the universe than any other element. As noted in the last post, all the elements except hydrogen and helium were formed after the Big Bang, spewed out by supernovas and the collisions of neutron stars. In general, heavy elements are less abundant because it takes more steps to produce heavy elements than light ones. But the curve is not smooth. The lightest elements after hydrogen and helium (lithium, beryllium, boron) are relatively rare, because they get used up in the nucleosynthesis of heavier elements. And there is a saw tooth pattern in the chart, because nucleosynthesis favors atoms with even numbers of protons. So we get lots of oxygen, magnesium, silicon, and iron, the main constituents of our planet. Lots of carbon too. Finally, iron (Fe) is more than 1000 times more abundant than might be expected based on a smooth curve. Iron nuclei are especially stable because binding energy, the energy that would be required to take the nucleus apart into its constituent protons and neutrons, reaches a maximum with iron. Here’s the famous curve of curve of binding energy (nucleons are protons and neutrons):

curve of binding energy

An implication of this curve is that if you can split a really heavy nucleus, of Uranium-235 say, into smaller nuclei (but still heavier than iron), you will release energy equal to the vertical difference between U-235 and its lighter fission products (not shown) on the vertical scale. This is lots of energy, way more than you get from breaking or forming molecular bonds in ordinary chemical reactions. And if you can fuse two light nuclei, of hydrogen say, into a larger nucleus, you can get even more energy. When we split uranium, we are recovering some of the energy that a star put into synthesizing elements heavier than iron, before or as it went supernova. When we fuse hydrogen, we are extracting energy from the Big Bang that no star got around to releasing.

Starting to figure this all out was part of a scientific revolution that made physics in 1950 look very different from physics in 1900. The new physics resolved a paradox in the study of prehistory. Geologists were pretty confident, based on rates of sedimentation, that the Earth had supported complex life for hundreds of millions of years. But physicists couldn’t see how the sun could have kept shining for so long. The geologists were right about deep time; it took new physics to understand that the sun got its energy from fusing hydrogen to helium (via some intermediate steps).

As the scientific revolution in atomic physics was picking up steam, it was natural to assume that it would be followed by a revolution in technology. After all, earlier scientific revolutions in the understanding of masses and gases, atoms and molecules, and electrons and electromagnetism, had been followed by momentous innovations in technology: the steam engine, artificial fertilizers, electrification, radio, to name just a few. But in some ways, the Atomic Age hasn’t lived up to early expectations. The atom bomb brought an earlier end to the Second World War, but didn’t change winners and losers. The bomb was never used again in war, and it’s a matter for debate how much the atom bomb and the hydrogen bomb changed the course of the Cold War. Nuclear energy now generates a modest 11% of the world’s electricity (although this number had better go up in the future if we’re serious about curbing carbon dioxide emissions). And a lot of ambitious early proposals for harnessing the atom never got anywhere. Project Plowshare envisioned using nuclear explosions for enormous civil engineering projects, digging new caves, canals, and harbors. Even more audacious was Project Orion, which developed plans for a rocket propelled by nuclear explosions. Some versions of Orion could have carried scores of people and enormous payloads throughout the solar system. Freeman Dyson, a physicist who worked on the project, said “Our motto was ‘Mars by 1965, Saturn by 1970.’”

On the purely technical side these plans were feasible. There were concerns about fallout, but the problems were not insurmountable. Nevertheless both Plowshare and Orion were cancelled. Dyson said “… this is the first time in modern history that a major expansion of human technology has been suppressed for political reasons.” The history of the Atomic Age  and its missed opportunities is a refutation of pure technological determinism. How or even whether a new technology is exploited depends on social institutions, politics, and cultural values.

We are stardust

10.4-9.86 billion years ago

The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.

Carl Sagan (h/t to commenter remanandhra)

There’s a long gap between the origin of the universe, the first stars, and early galaxies, and the origin of our Solar System and our planet Earth. If we were using a linear scale for our calendar, the Solar System would get started in September. Even on our logarithmic scale, Sun and Earth wait until late January. A spiral galaxy like the Milky Way is an efficient machine for turning dust into stars over many billions of years. But the earliest stars it produces are poor in “metals” (to an astronomer, anything heavier than helium is a metal). It takes generations of exploding stars producing heavier elements and ejecting them into space before a star like the Sun — 2% metal – can form.

And just last year, a spectacular discovery provided support for another mechanism of heavy element formation. Astronomers for the first time detected gravitational waves from the collision of two neutron stars, 300 million light-years away. Such collisions may be responsible for the formation of some of the heaviest atoms around, gold and silver in particular. So your gold ring may be not just garden-variety supernova stardust, but the relic of colliding neutron stars.

Alchemists thought they could change one element into another – lead into gold, say. But it takes more extreme conditions than in any chemistry lab to transmute elements. The heart of a star makes heavy elements out of hydrogen and helium; it takes a supernova to make elements heavier than iron. So it’s literally true, not just hippy poetry, that “we are stardust” (at least the part of us that isn’t hydrogen).

In the beginning

13.80 – 13.05 Gya (billion years ago)

Knowing what happened at the very beginning of the Universe is speculative. It depends on what the theory of quantum gravity looks like, which is up in the air. The theory of inflation (insanely fast growth before 10-32 seconds , after which the universe settled down to merely explosive growth with the Big Bang) may explain why the universe is flat, uniform, and not very lumpy. In 2014, it looked like we had direct evidence for gravity waves generated by inflation, going back just 10 sec from the beginning of the universe. But the jury is still out on this.

Later developments are more generally agreed on, although some of the exact times may need revision in the future. Strikingly, a lot of familiar astronomical objects, including stars and galaxies, are already around within 100’s of million of years. However early stars are short on metals (to astronomers, anything heavier than helium counts as a metal), and the early Milky Way is dispersed and fuzzy, not the barred spiral galaxy we know today.

New Year’s Eve, 2017

Some final year end matters:

2017 is the third year I’ve run through the history of the universe on this blog. It won’t be the last; I’ll do it again in 2018. As before, I will repost a lot of old material, but add some new stuff as well. Some readers of the blog and tweets, seeing stuff they’ve seen before, will decide to step off the carousel. I hope that they will encourage others to start following in their place.

Also, on the blog I occasionally take the opportunity to advertise my own work, some of it related to Logarithmic History, some of it not. So in the next few days I will be touting an old book of mine, Physical Attractiveness and the Theory of Sexual Selection: Results from Five Populations, soon to be available as a pdf, as well as a forthcoming article, “Kin selection and ethnic group selection.” Stay tuned!

And, finally, a reminder that this blog covers the history of one universe only.* According to some scientists, our universe may be just one in an ensemble of universes, the multiverse. It may be that some of these other universes are better arranged. In that spirit, I end as I have in other years, with this quotation from the science fiction writer Jack Vance:

The waiter departed to fill the orders. He presently returned with four tankards, deftly served them around the table, then withdrew.

Maloof took up his tankard. “For want of a better toast, I salute the ten thousand generations of brewmasters who, through their unflagging genius, have in effect made this moment possible!”

“A noble toast,” cried Wingo. “Allow me to add an epilogue. At the last moments of the universe, with eternal darkness converging from all sides, surely someone will arise and cry out: ‘Hold back the end for a final moment, while I pay tribute to the gallant brewmasters who have provided us a pathway of golden glory down the fading corridors of time!’ And then, is it not possible that a bright gap will appear in the dark, through which the brewmasters are allowed to proceed, to build a finer universe?”

“It is as reasonable as any other conjecture,” said Schwatzendale. “But now.” The four saluted each other, tilted their tankards, and drank deep draughts.

Jack Vance Lurulu p. 181

Happy New Year!

* Our species has a name, Homo sapiens. Our planet has a name, Earth. Our galaxy has a name, the Milky Way. Isn’t it time we figured out a proper name for our Universe, so as not to get it mixed up with any others? I suggest Om (rhymes with “home”). Surely somebody can do better?