Enough with the Galapagos Already

In the last post I wrote about the blue footed booby and its mating dance. The booby also curiously has another mating ritual where the male gathers twigs, leaves and other suitable nesting material to present to the female. The reason this is curious is that the boobies don’t actually build nests on the Galapagos, but lay their eggs directly on the rocks. The nesting material is useless to them. his is a nice example of the myriad proofs of evolution that appear anywhere you care to look. It is explicable only when you realize that the Galapagos blue footed booby must have evolved from a species of nest-building booby. And in fact, mainland boobies do build nests. They need them to protect their eggs from predators. But on the Galapagos those predators don’t exist. After arriving on the islands the boobies would have instinctively continued to build useless nests for awhile. But over the eons, natural selection would have progressively favored the sloppier boobies who wasted less and less time on unnecessary nest building, leaving more time to gather food. Ultimately nest building was dispensed with entirely.

But then why did the nest building mating ritual continue? It illustrates the peculiarities that happen with sexual selection, which is a special case of natural selection. Females choose mates based on rituals and physical traits that conspicuously highlight the male’s fitness, and the fitness of the genetic heritage he will pass on to their shared offspring. (Males also make similar choices but – at least in polygamous species – they can afford to be less picky.) Perversely, the traits that become the focus of sexual selection may be useless from the standpoint of survival, or even costly. The very fact that there is a cost which the male is able to carry evidences his fitness in the ways that ensure survival. The peacock’s tail is a classic example. It is useless in practice, expensive to maintain, and increases his visibility to predators. But the very fact that the peacock is able to support a great tail, shows the female that he is in other respects a great catch.

So by gathering useless twigs our blue footed booby is showing his prospective mate that he is first class. The behavior continues to have value as a signal of fitness even when the underlying motive for the behavior is gone. But even if twig gathering only shows fitness for an obsolete behavior it is unlikely to disappear anytime soon. The problem is that a male with a mutation that reduced the behavior would have a hard time breeding while females continued to look for it. On the other hand, a female that had a mutation that no longer found twig gathering “sexy” wouldn’t benefit since she would likely have sons with impaired twig gathering skills. And as long as other females are still looking for that her sons would have trouble finding good mates. (Talk about a chicken and egg problem!) Sexual selection works rather differently from natural selection generally – in natural selection ANY fitness advantage will be selected for and eventually predominate. But traits that have become a focus of sexual selection can persist even where they have negative impact on overall fitness, and – like the peacocks tail – can even spin out of control until they become a real burden.

As you’ve probably noticed, I find this stuff really fascinating. To explain why, let’s pause for a brief joke:

A man finds a magic lamp on a deserted beach and rubs it. A genie comes out and says “Hi, I’m a low grade Genie. I can only offer you one wish, so make it a good one.” The man thinks for a minute and says, “OK, I have always wanted to visit Hawaii. But I’m afraid of flying and get terribly seasick. I’d like a bridge built from my home in LA out to the islands.” The Genie takes out a pad and pencil and makes some calculations. Finally he says, “I don’t know, it’s over 4,000 miles, and the Pacific is up to five miles deep in some places. Can you come up with an easier wish?” The man thinks for a moment and says, “Well, another dream of mine is to understand women. What is it that they really want? What motivates them and what does it take to make them happy?” The Genie replies “About this bridge – two lanes or four?”

“Yes Dave,” you say, “that is a hilarious joke, and nicely told as well, but what does it have to do with blue footed boobies?” To which I reply “You obsequious moron, it should be obvious.” And here’s what I mean by that. Much about the relations of men and women, attraction, courtship, romance, fidelity, commitment and so on seems on the surface inexplicable – as though a process that ought to be simple and straightforward has broken down. But the only reason it seems inexplicable is because we expect it to be simple and straightforward – that people will meet, fall in love and mate for life, like pigeons and Catholics. But viewed with the perspective of evolution and sexual selection, it becomes apparent that there is nothing simple or straightforward about it at all. It is a game played for the highest possible stakes, and any possible advantages will be selected for. And – like the boobies – we will be burdened with all sorts of selective biases that may have made sense a million years ago on the plains of Africa, but now only provides juicy material for country-western songs. Why do men adorn themselves with BMWs and Rolexes and women with makeup, gowns and high heels? Why do guys bring their dates flowers and chocolates? Why do men seek out bimbos and women cads, and then complain because they act like bimbos or cads? The answer, of course, is that we are all just doing the dance of the blue footed booby. Now if you’ll excuse me, I need to attend to my twig collection.

[A great book on the subject of sexual selection is “The Red Queen” by Matt Ridley. And, yes, this will be on the exam.]