Deep archives: Irreducible beauty

Peacocks and audience at the Toronto Zoo

Were peacocks designed with this kind of audience in mind?

A while back I was searching for images of peacock feathers on Google, and I stumbled upon this article. It’s a piece by Stuart Burgess, an engineer who is head of the Department of Mechanical Engineering at Bristol University, and apparently also quite an opinionated creationist.

Burgess’ idea is that the peacock’s train feathers “contain an extremely high level of optimum design”, so much so that they provide evidence against Darwinian evolution. He thinks that the aesthetic features of the peacock are so complex, so contingent upon each other, that no step-by-step process of evolutionary change could have produced them. He’s right that these ornaments are highly complex, and that selection for this kind of extreme aesthetic feature presents a bit of a puzzle for evolutionary biology. To claim that the extraordinary complexity must be “irreducible”, however, is a big assumption.

The article provides a lot of amusing examples of twisted logic along the way. For example, one of the features that Burgess finds irreducibly beautiful is the fact that the peacock’s train forms a fan-like shape. This is because “the axis of every feather can be projected back to an approximately common geometrical center” – indeed, the body of the bird that grew them!

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Deep archives: Sex “pests” get more practice

Juvenile male peafowl practice their displays

Having finished my field work this year, I thought I’d keep up with this blog by writing about interesting things that other people have seen animals do.

To start: this BBC science news report on the discovery of a “sex pest” seal that attempted to mate with a penguin, brought to my attention by Rob Ewart (the original paper can be found here but you will need a subscription to the journal to read the whole thing).

Apart from the entertainment factor – the abstract to the scientific paper concludes, “we report a case of interspecific sexual harassment bridging the rank of vertebrate class” – there are a few interesting issues here. The first being, why on earth would the seal do this? The authors provide a few possible answers. Apparently these fur seals sometimes eat king penguins, so perhaps by some strange mis-wiring, predatory arousal translated into sexual arousal in this case. Alternatively, the seal may have been too young to find a real mate, desperation leading it astray. Or, intriguingly, the young seal could have been play mating, a form of practice for the real thing later on.

The second issue: why on earth would a scientific journal publish something like this? Is it really that unusual for hormonally-charged animals to make the occasional mistake? This year alone I witnessed a peacock give chase to a human female (with the characteristic “hoot” of excitement that accompanies all mating attempts), and I’ve seen several peacocks attempt the same with guinea fowl and squirrels. All of these events happened with males that were displaying intently but that hadn’t had any peahen visitors in quite some time. Is this paper really such a novel finding, or are the authors just as desperate as the seal?

On reflection, it’s probably important to document these unusual behaviours somewhere, since it would be an interesting outcome if they turned out not to be mistakes after all. Young peacocks, for example, will frequently display their undeveloped train feathers to each other (pictured above). This male-male display may seem futile, but I wouldn’t be surprised if the kind of dancing skill required later in life demands some practice. Similarly, in Costa Rica I remember hearing juvenile long-tailed manakins displaying long after the real mating season had ended, no doubt honing their skills for next year. There is even some evidence that the reason male manakins pair up for their co-ordinated display dances, even though only the dominant member of the pair will get to mate, is for the practice.

The full citation for the seal paper:

De Bruyn PJN et al. 2008 Journal of Ethology 26:295-297.

And two on long-tailed manakin displays:

Trainer et al. 2002 Behavioral Ecology 13: 65-69.

Trainer and McDonald 1995 Behavioral Ecology and Sociobiology 37:249-254.