The placenta and the pace of life

The poor old placenta. It really doesn’t get much public attention. And yet it does a crucially important job – acting as the interface between the mother’s blood supply and that of her developing foetus.

Every molecule of glucose, oxygen and many other essential compounds consumed by the voracious offspring passes across the placenta – from the mother’s blood to the foetus’. And waste products pass back the other way to be detoxified and excreted by the mother’s organs.

Given these roles, one might be tempted to see the mammalian placenta as a discreet anatomic servant, working tirelessly, unseen and largely without thanks for the mutual good of mother and foetus. Only to be discarded or eaten after birth and spared no further thought.

And occasionally be venerated in YouTube videos with mystical soundtracks:

But such a view underrates one of the most interesting organs that ever evolved.

For one thing, the placenta varies more among mammal species than almost any other organ. And research published today in the Proceedings of the National Academy of Sciences of the USA provides some clarity on how this diversity evolved. Continue reading The placenta and the pace of life

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)