Penis size may be driven by women (oh, and it matters)

How important is penis size?

Authors from the Australian National University, Monash and La Trobe provide the most complete answer yet: the size of a flaccid penis can significantly affect how attractive a man’s body is to women.

Writing in the Proceedings of the National Academy of Sciences (a journal commonly known by its initials as PNAS), Brian Mautz, Bob Wong, Richard Peters and Michael Jennions use a clever experimental manipulation of computer-generated imagery – CGI – to test the effects of variation in penis size relative to height and torso shape (shoulder width relative to waist width) on the attractiveness of male bodies to women.

While they found that torso shape was by far the most important determinant of attractiveness, penis size has about as much influence on attractiveness as height.

It’s the kind of science made for easy-reading 100 word news-porn in the tabloid press (“Size really does matter”). Or for wowser columnists to work up a morning’s indignation that a scientist somewhere did something interesting when everybody knows the rules:

Scientists should be finding new ways to extract coal-seam gas or cure the cancers that tend to afflict late-middle-age columnists (see the recent controversy when Fox News attacked Patricia Brennan’s research on duck penises).

If Tom Waterhouse wasn’t so busy swotting for Friday night football, he’d have already installed Mautz as hot favourite for the next igNobel Prize (for science that makes you laugh and then makes you think).

And yet for such a tabloid-ready topic, the paper itself is a study in how science should proceed in sober and restrained steps.

Evolution of penises

Genitalia tend to vary more dramatically than almost any other physical trait. And evolutionary biology has made stunning progress in resolving why.

For the most part, studies of animal penis size and shape have focused on the effectiveness of various structures in delivering sperm to where it needs to be, in removing sperm that a female had received from previous mates, in stimulating the female to use that male’s sperm, or even inflicting damage on the female so she would not mate again.

One of the more striking features of the human penis, when compared with other primates, is its length. Relative to body size, the human penis dwarfs that of bonobos, common chimpanzees, gorilla and orangutan. And our erect stance and face-to-face social interactions make the penis a highly conspicuous feature.

That conspicuousness has led anthroplogists and pop-scientists alike to speculate on the potential for penises to act as a sexual signal. Some have even suggested that a large penis may be a signal of more general health and vigour, and that the evolutionary loss of the human baculum (penis bone) may make the penis an honest signal because size and arousal can’t be faked. Continue reading Penis size may be driven by women (oh, and it matters)

Hands are for fighting. Not for talking.

Albrecht Dürer, A Study of Three Hands (c.1490).
Albrecht Dürer, A Study of Three Hands (c.1490).

A few weeks ago I found myself reading up about the evolution of language in preparation for a talk I gave to the Applied Linguistics Association of Australia’s conference in Perth. It turns out the evolutionary forces that shaped humanity’s capacity for language remain far from well resolved.

Just about everybody agrees that language is awfully useful, but how much of that usefulness reveals the purpose for which language originally evolved? Do we owe the gift of the gab to the fact language can be used to talk our way out of trouble, or to eavesdrop, or to cooperate with others, or to trade, or to court and seduce mates?

Some of the most influential thinkers in this area, including Noam Chomsky, have argued that our capacity for language might be a byproduct of adaptations with little to do with communication and lots to do with computation. Perhaps, they argue, language is a recent embellishment to our evolved capacity to calculate quantities, to navigate, and discern the complex web of who-owes-what-to-whom on which human social life depends.

While the researchers involved each have their favourite theories, nobody seriously claims that language has a single adaptive purpose. Few traits, and particularly not complex traits like language, have a single adaptive function. The excitement and the controversies surrounding these traits arise out of questions about the relative importance of different evolutionary forces, and how they act. Continue reading Hands are for fighting. Not for talking.

Is human intellect on the downward slide?

Did human intellectual capacity peak 600 years before Plato? Raphael’s Scuola di Atene fresco in the Vatican, 1511. Wikimedia commons

I would wager that if an average citizen from Athens of 1000 BC were to appear suddenly among us, he or she would be among the brightest and most intellectually alive of our colleagues and companions, with a good memory, a broad range of ideas, and a clear-sighted view of important issues.

So Stanford geneticist Gerald R. Crabtree begins back-to-back Forum pieces for Trends in Genetics, entitled “Our Fragile Intellect” (Parts I and II). Crabtree’s thesis: humanity is “almost certainly” losing its superior intellectual and emotional capacities.

Crabtree doesn’t seem to be arguing for the intellectual vibrancy of the Akademia or the Lyceum. These places, and their celebrated occupants like Plato and Aristotle graced Athens only 600 years later, well beyond Crabtree’s inferred date of humanity’s intellectual zenith.

And he doesn’t confine himself to Athens. “I would also like to make this wager”, he goes on, “for the ancient inhabitants of Africa, Asia, India, or the Americas, of perhaps 2000-6000 years ago.” He’s arguing that humans – throughout the world – have been steadily losing their marbles for the last three to six millenia.

Well, Professor Crabtree, I’ll see your Athenian intellectual Titan. And I’ll raise you a bottle of 1998 St Henri and a $100 book voucher.
Continue reading Is human intellect on the downward slide?

When men were boys – demographic data shows male puberty starts 4 years sooner than it did in 1800

You’ve no doubt heard that girls are entering puberty earlier than they ever have before. It’s one of those science-lite stories beloved of tabloid papers and current affairs programs. One recent article had 10 to 15 percent of American 7 year olds showing the first signs of breast development.

It’s one of those problems that has folks scratching around for an answer. Toxic chemicals in the environment, including those that fake the effect of hormones, often get the blame. Diet – specifically the overnutrition that’s also causing childhood obesity to balloon – is another popular culprit.

There are plenty of reasons to be concerned. Hormonal disruption can cause all sorts of diseases, including breast cancer. Likewise, obesity can lead to type II diabetes, coronary heart disease and many cancers.

Figure 1 from Goldstein's paper, shoing the 'accident hump' in male mortality.

Beyond these problems that might beset girls later in life, maturing too fast can make life difficult for little girls. Young girls can be notoriously precocious, and it isn’t hard to imagine that an 12-year old who looks 17 could find her world a bewildering and even dangerous place.

The start of breast development is thought to signal the beginning of puberty, and can be measured easily. Even better, the age at which a girl reports her first menstruation gives and unambiguous and easy to remember measure. And records go back a very long time, confirming that girls are experiencing menarche, on average, at younger ages.

But what about boys? It isn’t quite as easy to measure the onset of puberty in boys as it is in girls. An innovative new paper by Joshua R. Goldsteinat the Max Planck Institute for Demographic Research in Rostock, Germany, makes use of a rather unfortunate quirk of male demography to do so.

Both girls and boys experience declining mortality rates throughout childhood and early adolescence. For a brief period in the early teens, as girls enter menarche, their mortality rate slowly begins to rise, and it continues to do so gradually until around 50, at which time it takes off (see Figure 1).

About half a year after girls’ mortality begins to rise, boys also begin to die at much faster rates, and their chances of dying outstrip those of women until they reach about 30 years old.

This “mortality bump” is a famous feature of human demography. It occurs because pubescent and young adult boys suddenly become much more likely to die in accidents and violence. In a very short time, many boys go from relatively cautious children to wild thrill-seekers. Evolutionary psychologists reckon the burning desire to take risks comes from a furious jostling for respect and acceptance among male peers, and an urge to show off to girls.

Likewise, Martin Daly and Margo Wilson’s exceptional work on the causes of homicide shows that the most common form of killing, in which young men kill other, unrelated young men, tends to be the tip of an iceberg of simmering masculine rage. The urge to retain this respect and to compete with rivals can turn an otherwise innocent look or bump into a violent confrontation, some of which end in homicide.

Goldstein recognized that demographic records hold valuable information about the timing of male adolescence. Instead of finding out when each boy reached a particular landmark in development and then calculating the average age, he realized that the timing of the ‘accident hump’ could reveal the average age at which whole cohorts begin to behave like adolescents,

Figure 2 from Goldstein's paper, showing the decrease in age at which the accident hump manifests.

Sweden has kept fastidious demographic records for over 200 years, and several other countries have done so for almost as long. It turns out that over two centuries, young men have begun to mature a full four years earlier (see Figure 2).

Just as early pubescence in girls raises unique worries, so too we should  worry about ever younger men entering the period of anger, recklessness and relentless striving to impress peers and possible partners.

It is a problem that has long concerned Sir Peter Gluckman, the Chief Science Advisor to the New Zealand. He wrote a fabulous book, Mismatch: Why Our World No Longer Fits our Bodies, in which he discusses this and other ways in which our evolved bodies are no longer adapted to modern conditions.

Gluckman told the New Zealand news site that “MRI scanners have looked at the brain over time to see how it matures and several studies have shown quite dramatically that the last parts to mature deal with things like logic, judgement and wisdom. Those scans show they may not be mature until people are 25 to 30.”

While modern safety standards in developed nations probably make industrial and agricultural accidents as well as accidental drowning and homicide less likely than they were in 1811, we have invented plenty of new ways for young men to kill themselves since then. Foremost are personal firearms and that deadliest of weapons, the motor car.