Tag Archives: sex

What do women want?

1.38-1.31 million years ago

As we noted in the last post, human females conceal ovulation (no chimp-style monthly sexual swellings) but advertise nubility (with conspicuous fat deposits). Presumably this has to do with sexual selection, via male mate choice. But sexual selection may have operated in the opposite direction, on male anatomy, as well.

Males of most primate species have a baculum, or penis bone. Human beings and spider monkeys are the exceptions. (A mnemonic: the mammals with penis bones are PRICCs – primates, rodents, insectivores, carnivores, chiropterans=bats.) The baculum helps to retract the penis when it’s not in use, so males in our species, lacking a penis bone, have more conspicuous dangling organs than most primate males.

This information comes from a recent book The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World ­– and Us, by Robert Prum. Prum also cites a paper arguing that Adam’s “rib” (Hebrew tsela), the thing God used to make Eve (Genesis 2:21-23), was actually his baculum, providing a creationist explanation of “congenital human baculum deficiency.” The book contains lots of interesting tidbits like this, although its central argument – that sexual selection via mate choice is largely a result of non-adaptive aesthetic preferences – is shaky.

Men’s penises lack something else found in most primate species: most male primates have keratinized spines on their penises. But a gene involved in the development of penis spines got turned off in our evolutionary lineage, some time after our split with chimps, but before our split with Neanderthals. We’re not sure why. Penis spines might be favored in promiscuously mating species if they help one male dredge out sperm left by earlier matings with other males. So (relative) monogamy in our lineage might remove the evolutionary advantage of spines. But a non-spiny penis might also be less sensitive, and make for more prolonged intercourse.

If all this doesn’t answer the question “What do women want?”, it at least narrows down the possibilities a bit: not men with bony, spiny penises, apparently.


Calories and curves

1.46-1.39 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.)

When you were a tadpole and I was a fish

1.17-1.11 billion years ago

The Boring Billion rolls on. The atmosphere is one percent oxygen or so thanks to photosynthetic bacteria and algae. The ocean still largely anoxic and thick with sulfates and sulfate-eating bacteria. Eukaryotes have been around for a while, and are diversified, although still all single celled (as far as we know).

Sexual reproduction begins with eukaryotes, and by now some groups are presumably differentiated into male and female. For those of you who are not bdelloid rotifiers, here’s a poem for Valentine’s Day, by the biologist Langdon Smith. Martin Gardner has a nice account of the poem, in his book “When you were a tadpole and I was a fish,” and here’s a great video of the poem spoken by Jean Shepherd.

By Langdon Smith (1858-1908)

When you were a tadpole and I was a fish
In the Paleozoic time,
And side by side on the ebbing tide
We sprawled through the ooze and slime,
Or skittered with many a caudal flip
Through the depths of the Cambrian fen,
My heart was rife with the joy of life,
For I loved you even then.

Mindless we lived and mindless we loved
And mindless at last we died;
And deep in the rift of the Caradoc drift
We slumbered side by side.
The world turned on in the lathe of time,
The hot lands heaved amain,
Till we caught our breath from the womb of death
And crept into life again.

We were amphibians, scaled and tailed,
And drab as a dead man’s hand;
We coiled at ease ‘neath the dripping trees
Or trailed through the mud and sand.
Croaking and blind, with our three-clawed feet
Writing a language dumb,
With never a spark in the empty dark
To hint at a life to come.

Yet happy we lived and happy we loved,
And happy we died once more;
Our forms were rolled in the clinging mold
Of a Neocomian shore.
The eons came and the eons fled
And the sleep that wrapped us fast
Was riven away in a newer day
And the night of death was passed.

Then light and swift through the jungle trees
We swung in our airy flights,
Or breathed in the balms of the fronded palms
In the hush of the moonless nights;
And oh! what beautiful years were there
When our hearts clung each to each;
When life was filled and our senses thrilled
In the first faint dawn of speech.

Thus life by life and love by love
We passed through the cycles strange,
And breath by breath and death by death
We followed the chain of change.
Till there came a time in the law of life
When over the nursing sod
The shadows broke and the soul awoke
In a strange, dim dream of God.

I was thewed like an Auroch bull
And tusked like the great cave bear;
And you, my sweet, from head to feet
Were gowned in your glorious hair.
Deep in the gloom of a fireless cave,
When the night fell o’er the plain
And the moon hung red o’er the river bed
We mumbled the bones of the slain.

I flaked a flint to a cutting edge
And shaped it with brutish craft;
I broke a shank from the woodland lank
And fitted it, head and haft;
Then I hid me close to the reedy tarn,
Where the mammoth came to drink;
Through the brawn and bone I drove the stone
And slew him upon the brink.

Loud I howled through the moonlit wastes,
Loud answered our kith and kin;
From west to east to the crimson feast
The clan came tramping in.
O’er joint and gristle and padded hoof
We fought and clawed and tore,
And cheek by jowl with many a growl
We talked the marvel o’er.

I carved that fight on a reindeer bone
With rude and hairy hand;
I pictured his fall on the cavern wall
That men might understand.
For we lived by blood and the right of might
Ere human laws were drawn,
And the age of sin did not begin
Til our brutal tush was gone.

And that was a million years ago
In a time that no man knows;
Yet here tonight in the mellow light
We sit at Delmonico’s.
Your eyes are deep as the Devon springs,
Your hair is dark as jet,
Your years are few, your life is new,
Your soul untried, and yet –

Our trail is on the Kimmeridge clay
And the scarp of the Purbeck flags;
We have left our bones in the Bagshot stones
And deep in the Coralline crags;
Our love is old, our lives are old,
And death shall come amain;
Should it come today, what man may say
We shall not live again?

God wrought our souls from the Tremadoc beds
And furnish’d them wings to fly;
He sowed our spawn in the world’s dim dawn,
And I know that it shall not die,
Though cities have sprung above the graves
Where the crook-bone men made war
And the ox-wain creaks o’er the buried caves
Where the mummied mammoths are.

Then as we linger at luncheon here
O’er many a dainty dish,
Let us drink anew to the time when you
Were a tadpole and I was a fish.

Between Darwin and Saint Valentine

Yesterday was Darwin’s birthday (and Lincoln’s). Tomorrow is Valentine’s Day. Here’s a post appropriate for either day.

Imagine sex worked like this:

You’ve been feeling bad lately, getting sick a lot. You’re not at your best. You find someone who seems to be in better shape. One thing leads to another and you wind up acquiring body fluids from the other party – and picking up some new genes from them. The new genes help a lot in fighting off infection. You’re feeling better now.

Reproduction? That’s another matter, nothing directly to do with sex. When you reproduce, your offspring will carry all the genes you happen to have at the moment.

Also, I forgot to mention that you’re neither male or female – the gene exchange could have gone in the other direction if you’d both been in the mood. And your partner in the adventure above might not even have been the same species as you. (Just what counts as a species here isn’t well-defined.)

This is more or less how bacteria work out sex. (Joshua Lederberg got the Nobel Prize for figuring this out.) Eukaryotes (you’re one of them) mostly do it differently, combining sex and reproduction. It’s the story you learned in high school about passing on half your genes to a gamete (sex cell), which joins with another gamete to make a new organism.

Most eukaryotes also have two sexes. The best theory we have about why that got started goes like this: Most of the DNA in a eukaryote cell is in the nucleus. But a small fraction is in the mitochondria, little powerhouses outside the nucleus that started out as bacteria, and got domesticated. Imagine that two gametes join together, and combine two sets of mitochondria. There’s a potential conflict here. Suppose your mitochondria have a mutation that lets them clobber your partner’s mitochondria. This is good (evolutionarily speaking) for the winning mitochondria, but very likely to be bad for the cell as a whole. Better for the cell as a whole is if one gamete, acting on instructions from the nucleus, preemptively clobbers all their own mitochondria, so that all the mitochondria come from just the other gamete. This is the beginning of what will eventually lead to a distinction between sperm and eggs, pollen and ovules, male and female. Which means you got all your mitochondrial DNA from your mom, something that will turn out to be important when we look later in the year at geneticists unraveling human prehistory. This is also an example of how selection at one level (within cells) can conflict with selection at another level (between cells). We’ll see such multilevel selection again and again, for example in the evolution of complex human societies.

Sex has to be highly advantageous, although we’re not sure exactly what the advantage is. When eukaryote species give it up, they don’t seem to last long. Dandelions reproduce asexually: based on what we see in other organisms, they probably won’t be around for long, evolutionarily speaking. There’s one mysterious exception, tiny animals called bdelloid rotifers which have been reproducing asexually for tens of millions of years . For readers who are not bdelloid rotifers: Happy Valentine’s Day tomorrow! We’ll have an appropriate evolutionary post up tomorrow

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).

My nights were sour, spent with Schopenhauer

April 1997 – May 1999

In 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.

Sexual intercourse began in 1963

October 1960-October 1964

Sexual intercourse began
In nineteen sixty-three
(which was rather late for me) –
Between the end of the Chatterley ban
And the Beatles’ first LP.

Up to then there’d only been
A sort of bargaining,
A wrangle for the ring,
A shame that started at sixteen
And spread to everything.

Then all at once the quarrel sank:
Everyone felt the same,
And every life became
A brilliant breaking of the bank,
A quite unlosable game.

So life was never better than
In nineteen sixty-three
(Though just too late for me) –
Between the end of the Chatterley ban
And the Beatles’ first LP.

Annus Mirabilis, by Phillip Larkin