Field of Science

A comment to Satoshi Kanazawa

Satoshi Kanazawa runs an interesting blog that has one major, major flaw: you cannot comment on his posts. That is in addition to whatever else he says, which I sometimes disagree with. His newest post, for example, which reiterates the usual notion that the tail of the male peacock is utterly useless, and are only there to impress females:
A prime example of a handicap is the peacock’s tail. The long, elaborate, and ornate tail of a peacock does not have any adaptive value; it does not serve any tangible, useful purpose that would aid the survival of the peacock. In fact, it only harms its survival chances. Peacocks with longer, more elaborate trains are easier for predators to catch and kill than fellow peacocks with shorter and simpler trains. So they only have costs and no benefits. But that, according to Zahavi, is precisely the point. Peacocks are advertising to peahens “Look, I am so genetically fit and I can run so fast that I can still evade the predators with this huge thing hanging from my ass! Them other guys ain’t so fit and the only reason they can evade predators is because their trains are shorter. They wouldn’t be able to evade the predators if their tails are as long as mine! Now whose genes would you like your offspring to carry?” And peahens indeed do prefer to mate with peacocks with longer, more elaborate, and more symmetrical tails that are biologically very expensive to maintain, so that their male offspring will also sport long, elaborate tails that attract females of their generation.
Which is total bullshit. Go see real peacocks, and you might notice that they raise their tailfeathers when people get too close... because they want to mate with them? I don't think so. More likely, to scare them away by their huge size - plus confuse them with the eyes on the feathers. As I've suggested once before.


  1. So out of curiosity, do you reject the Zahavi handicap principle altogether, or do you just doubt its applicability in the case of the peacock's tail?

  2. Fair question. I don't rule it out, but I also don't know of any really good demonstration of it applying anywhere, where the trait has been shown not to have another function.

  3. My husband is currently remodeling a house that has a large backyard. In this backyard is a peacock, "Percy" and two large yellow labs. The homeowner told my husband that when they brought the lab puppies home, the puppies took off running towards Percy. Percy immediately "spread" out his feathers and starting "shaking" them a little bit. The dogs have never bothered Percy in the five years the homeowners have owned them. Sorry it's not a scientific explanation!

    Thanks for having such a great blog.


  4. Jan, thanks a lot for sharing that story! It's just what I expected. While it's anecdotal evidence, it is not to be dismissed. I promise next time anyone mentions about sexual selection, or peacocks tails, I will bring this up. I need to film this. Perhaps I'll make a little side-project out of it, too.


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