I recently was sent a link to this really wonderful video about birds of paradise. Watch the video, you won’t regret it. The birds of paradise are out of this world:
(from Australian Geographic image source)
But beautiful coloration and weird mating rituals are found, although in not quite as extreme form, in many other birds, as well as other groups of animals. Almost invariably it is the male that wears the gaudy suit:
The bright red one is the male, the subdued grey one is the female. She has a nice and functional tail, while he has to negotiate the brambles with a ridiculously long and easily damaged tail feathers. Why is it always the male that goes to such extremes in order to obtain a mate? A pretty good answer is offered by the standard evolutionary theory, sexual selection, which goes back to Charles Darwin. Basically, being brilliantly colored, or having a very long tail (like peacocks), and being able to dance for hours is a very accurate signal of male quality. You may lie to the girl which you met in the bar about your bank account, but if you have crooked or rotting teeth in your mouth, she will know you can’t afford a good dentist. And bird females know this, too. So they choose brightly colored males, and then the evolution pushes this to ridiculous extremes.
In humans, by the way, males and females are relatively similar (in the biological jargon, the degree of sexual dimorphism is quite low). In the evolutionary precursors of the genus Homo the males were much larger than females, like in chimps and, especially, gorillas. The most likely explanation is that in humans between-male competition was greatly reduced because of pair-bonding and the need for males to provide food for their mate while she nurses the baby.
But this lack of significant sexual dimorphism refers just to biology, and humans have culture. A human male doesn’t need to grow bright feathers or a long tail, he can put them on. And we sure do.
(image from badgerinvaders)
Detail from Tavolette di San Bernardino, 1473. Gallerie Nazionale dell’Umbria (photograph by the author)
But unlike in birds, it is not always the male who is the most gaudily dressed.In fact, it is rare for the male costume to be more colorful than the female’s. I looked through a whole lot of plates in The History of Costume(Braun & Schneider – c.1861-1880) and here’s one that seems to fit the avian model best:
Most of the time, if men wear colorful and elaborate dress, so do women:
And when men tone down the colors, so usually do women. So a century after the ‘decadent’ fashions of Ancien Regime, we have this:
The cultural variability, and how fast it can change with time, is extraordinary. So what kind of theory do we have that can explain such variation and its dynamics? Is there anything in cultural evolution approaching the rigor and empirical support that the theory of sexual selection has in biology?