Penis size and Peacocks’ Eyes

150 years ago, Darwin first discusses sexual selection in The Origin… then comprehensively in Descent of Man. The problem was why some characters seem non-adaptive and not governed by natural selection. A famous example is the tail of the male peacock, who Darwin noticed desperately seeks “a spectator of some kind”, and, “will shew off his finery before poultry, or even pigs”.
What advantage this behaviour has for survival is not obvious: the cost to the male in producing his stunning apparel mustn’t exceed any survival benefits but the way that Darwin carefully constructs a considered and logical argument demonstrates his exemplary working. He shows that the benefit is real and great; not so much involved with individual survival, it is related to the reason for surviving. Reproduction.
Darwin cleverly identified the benefit that outweighs the cost of cumbersome and garish plumage, also predicting some optimal balance in the economy of nature. Costs may define the fine line between getting it right and “going all Liberace”, but the converse of underselling is worse: peahens are a lot fussier than Darwin thought. Recently, the number of ‘eye-spots’ were adjusted without shortening the tail; typically there are about 150 of them, shown to be optimal. Less, and mating success dwindled until males with fewer than 130 had less chance of pulling a peahen than Quasimodo with a feather duster stuck up his arse. In fact, girl power dictates that even two dusters might not be enough; there is an inbuilt, self-perpetuating inflation that drives up costs, but also profit margins. This positive feedback loop is called “Fisherian Runaway” after R.A. Fisher who described it (1915, 1930). For the peahen, choosing a mate who has a beautiful long tail increases the chance of her male offspring growing one, and so also be attractive. Of course, for her there is very good reason to be choosy. Males can and want to spray their sperm around willy‑nilly, but producing an egg and offspring levies a prohibitive tax upon her metabolism.
Whilst researching the evolutionary ecology of African antelopes I couldn’t fail to notice the sexually selective adornments that they boast. Very horny! From the captivating spiral of the Kudu to the seductive Arabian curve of the Giant Sable’s scimitar, it’s advertising with a full page spread. Of course, take out too many column inches like the Irish Elk, and nature’s economy becomes bankrupt, a recession destined for extinction. But get it right, and … well, there was an impala I knew with forty females and territory the size of a nature reserve. He was called “Lucky Boy”.
Darwin could only sketch out the details of how sexual selection works. As with natural selection and genetics, he couldn’t have been privy to the peacock’s immune system, the health of which is strongly linked to his tail. This was also discovered recently, but is likely to be duplicated in other species. For example, stick an extension onto a long-tailed widow bird and other than ending up with a longer-tailed widow bird, you’ll also gain a queue of fawning females. Impressive plumage makes a great advert for virility, because if there’s no parasites depleting your immune system, then you should be a healthy specimen. Of course, it is this underlying adaptive advantage that is really being passed on to any offspring. But there’s more for the female than just genetic imperative. Spotting a brightly-coloured, prancing dandy is adaptive; it saves time searching for a mate reducing her costs and increasing survival.
Avoiding jokes about size mattering, for males given a short straw, there is hope. When costs in choosing are low, females don’t necessarily prefer only one male ornament, selecting between those on offer irrespective of the costs to the males in their production. Again, our peacock’s tail length is an indicator of antibody production while the eye-spots are a measure of phagocytic defences. Sometimes this doesn’t work as well as it might. Embellishments exhibit varied responses to an affliction. The female may then be drawn by an unaffected attribute, costing her dearly if she’s actually selected a pox-ridden impostor. Fisher’s process can produce multiple preferences and the males must follow by ensuring their bits are preferred, whatever and to whomever the price. Rutting and lekking males, like Lucky Boy and Darwin’s peacocks and stags, are good examples of this, strutting their various stuffs. But it can also be introduced artificially: preferring beaks and plumage, female zebra finches also like flashy leg bands, like wearing a Rolex.
Similarly, Darwin had a lot to say about human adornment, specifically beards. He traced the roots of facial hair to “an ancient progenitor” which was then acted on by sexual selection. Yet again modern studies prove that he was right. There is a strong sexual connotation to facial hair because males use it to advertise their social rank and virility. Like muscle mass and penis development, facial hair growth is influenced by testosterone levels, and is like wearing a sign on your chin saying, “hair today, gonads tomorrow”, which must make the World Beard & Moustache champion the sexiest man in the world. At the time of writing, his name is Mr Passion. Oddly enough, occidental society has recently tended away from beards, associating them with antisocial psyches or disturbed pasts, as in “hiding behind a beard”.
Darwin’s own beard has achieved iconic status, the bearded version being more readily called to the minds of most than the young man. However, my own personal experiences provide little support for sexual selection of male facial hair. I have at times grown a beard in various styles, its presence more dependent on my pennies than my penis, and I’m sure it hardly ever contributed carnally. Clearly it was never long enough. I am now habitually clean-shaven, but I wonder what private thoughts Darwin was entertaining as he sat there in his dotage looking like old Father Time. I mean, his was so long that he could have draped it over a shoulder. Not necessarily his own.
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UPDATE: Interesting contribution to the peacock tale…
These feathers weigh about 300g and can exceed 1.5m, so it’s expected that the male birds would be making a significant sacrifice in their flight performance for being attractive—possibly giving up their lives if the train restricts escape from predators such as tigers and leopards in their natural environment …. filmed the take-offs of birds carrying full plumage in 3D, and then filmed the same birds taking off without their trains. The display feathers, which naturally moult at the end of the breeding season, were clipped to judge the change in take-off performance between the two states … found there was no significant difference.
Peacock’s train is not such a dragScience and technology news, Univ. Leeds, 18 September 2014

About JFDerry

Writer. Darwin, science & more. 4 books: Piospheres, Darwin in Scotland, Serial Killers. Current project is THE DISSENT OF MAN. Born near London, raised near Primrose Hill and in Lincolnshire, and studied at the Universities of Bangor, York and Edinburgh for degrees in Biochemistry, Bioelectronics and Biological Computation, and a PhD in African Ecology. Mainly working in British and African universities, but also in Spain, Brussels, Mongolia and Australia, to date, publication history is mostly in academic journals, on aspects of computational biology, pastoralism and on Charles Darwin and evolution. However, also written for several national newspapers, various governments, several major record labels and independent book publishers. Fiction has appeared at the Edinburgh International Book Festival and poetry is at the Human Genre Project. Lives in Edinburgh, with partner and their two daughters.
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4 Responses to Penis size and Peacocks’ Eyes

  1. Excellent article. I wonder if Emma might have thrown some light on Charles’ iconic beard! So willies and beards for guys. Given we are the one and only naked ape, it seems rather surprising we didn’t go in for brighter skin colours and bolder patterns as well, but the sexes are pretty much plain and identical. I guess our manes, if left uncut, are pretty impressive. Amazing that for once, culture seems to have overridden nature. Why would the majority of women dislike a sexually-selected character and prefer a beardless partner? Women, I invite you to comment…

  2. Katiemjy says:

    Simple. Beards are scratchy!

  3. sobk13 says:

    This was a really lovely article to read, for its humour, knowledge and insight. For me at least, as a woman and a casual observer of the human condition, indicators seem to change and shift with time, as the article suggests, depending on our environment and our ability to predict or piece together characteristics and qualities that make the man.

    Right now it seems as if we are living on credit, having exchanged our slightly cruder barter system (my breasts for your beard) into something a little more sophisticated (your manners for my mammaries). Perhaps the explosion in population numbers has meant that in some parts of the world, the need to mate with haste is no longer there, coupled with economic realities like women now being able to go to work and earn their own income. Still, biologically, I think we do choose men subsconsiciously for what they can offer our offspring, but I think for the reasons above and more, women are now focusing on the male mind more than they used to. Which may be why you poor guys have had to incorporate things like preferred table manners and loo seat etiquette into your peacocks’ repertoire :-)

    The mating process then, is perhaps slower, more deliberate but not necessarily more accurate. Like the peacock that has too many spots due to illness, those false indicators, to my mind, also manifest in communication, with men and women learning to adapt so well that they become chameleons. I imagine this must be a survival instinct in itself but it does mean that as we are forced to become more sophisticated in a world with more choice that more indicators manifest themselves, both real and illusory. It’s a mater’s minefield.

    Ultimately, if the lights go out and the heating stops, women may go back to basics. Strong, muscular men, more like the protectors of yore, may become the most sought after male specimens. But there’s a catch, too – women like me are drawn to strong men, designed for rugged existence, despite living in an environment which is more urban jungle than Amazonian rainforest. Are women like me falling behind the curve or engineering it? I suspect it’s a bit of both (it’s no good being rugged if you can’t understand the finer points of Nietzsche or nuclear physics to get you out of a tight spot) , but in the end I think most women will choose a man who displays the greatest inner strength and stamina in their environment, which seems to me to be how we’ve always chosen our soul’s mate.

    PS. I wonder whether men have their own unique cerebral selection process for women?

  4. Pingback: Wine, Rorschachs, and naked rugby | Limpid Lech's finds

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