The Flight of the Iguana (10 page)

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Writing in the journal
Nature,
Eric Charnov and James Bull have offered a conceptual model that might make evolutionary sense of the whole range of ESD cases. “We propose that labile sex determination (not fixed at conception) is favoured by natural selection when an individual's fitness (as a male or female) is strongly influenced by environmental conditions and where the individual has little control over which environment it will experience.”
Control
is the key word. If an organism can't completely control where it's going (like a
Bonellia
larva, riding helplessly on the sea currents), then maybe there is compensatory value in
retaining control over what sort of being (male or female) it will be when it gets there.

This might sound like something from
Alice in Wonderland,
but in truth there is nothing illogical about it. The apparent reversal of logic merely goes against our preconceptions. We think of sexual identity as virtually a prerequisite to existence. Under the Charnov-Bull model, by contrast, sex determination is just an intermediate step on the long path toward what might be called (in California, anyway) self-actualization.

“To illustrate,” say Charnov and Bull, “if an individual finds itself in an environment where it can become a below average female or an above average male, selection will favor its becoming male because it can pass on more of its genes than if it were female.” And vice versa. “Selection may therefore favour ‘environmental sex determination' (ESD) because of the control it allows an individual.” Fine, that seems reasonable—but several complicated assumptions lie behind this simple statement.

One assumption is that the evolutionary fitness of an individual (as tallied, always, by how many offspring survive) is measured relative to other individuals of the same species
and the same sex.
In other words, a male alligator competes only against other male alligators for the right to leave a large share of descendants. Another assumption made by Charnov and Bull is that the environment in question is patchy, with some patches conferring heightened advantage on females, other patches conferring heightened advantage on males.

From these two givens, Charnov and Bull argue that natural selection “should most strongly favour ESD when 1) the offspring enters an environment, away from the parent, which has a large effect on its lifetime fitness . . . and 2) the offspring and the parent have little control (or predictive ability) over which patch type the offspring enters. These conditions make it unfavourable to determine sex at conception because of the possibility that a male will enter a patch that is much more favourable
for a female, or the reverse.” So ESD allows an individual to match its own sexual identity with the particular patch of environment that will heighten its prospect under that identity—not by choosing the patch, but instead by choosing the sexual identity.

Among alligators the patch differences seem to be a matter of temperature at which the eggs are incubated. Nests built on dry levee (according to that elaborate field study, done in Louisiana) tend to stay warmer than ninety-three degrees F. and to yield males. Nests built on wet marsh tend to stay cooler than eighty-six degrees and to yield females. In either case the environment during incubation may have a large effect on lifetime fitness, because that temperature difference translates to size of the individual at hatching, which in turn affects how soon the individual will reach breeding size. Females have a greater need than males do to reach breeding size quickly, because their allotted span of breeding years is much shorter. (That part applies also to humans, providing an evolutionary rationale for why prepubescent fifth-grade boys should find themselves mystified by their classmates' burgeoning breasts.) The consequence of all this is that cool nest temperatures—which turn out
larger
baby alligators—give most females a head start toward breeding size. So if an individual alligator is relatively small at the time of hatching, it will fare better in the lifelong Darwinian competition as an average male than as a below average female. And, fortunately, ESD will have already matched its sex to its best prospects.

But what about those ridiculous
Bonellia?
They seem to be covered equally well by the Charnov-Bull model. In this case the patchiness of the environment is a matter of presence or absence of female
Bonellia.
The larvae can't control where they travel, and the adult females are sessile, traveling nowhere at all. When any one larva encounters a female, that fact has great effect on its lifetime fitness, because it means that the little devil will have an opportunity to mate. Otherwise he would be forced to take his
own chances as a female, with some jeopardy of permanent spinsterhood. ESD again is the matchmaker. ESD lets him be all he can be.

The moral: Identity is such a crucial affair that one shouldn't rush into it.

No doubt that seems perfectly natural to a spoon worm. Some of us “higher animals,” on the other hand, don't have the luxury of such a convenient biological postponement. And probably our
Bonellia
would be horrified, or silenced in pity, if he (or she, depending) could see the desperate, bizarre ways by which we humans must try to cope with the intractable dilemma of self.

A Tempered View of Canine Evolution

Let's begin slowly, with a relatively safe statement: Not all dogs are bad.

We Americans live today amid a plague of domestic dogs, a ridiculous and outrageous proliferation of the species, true, but not every one of those animals is damnable beyond redemption. Not every one has had its soul twisted by misery and neglect, spending long days chained or fenced within a tiny yard and taking its revenge by barking at the neighbors. Not every one is ill-trained, intermittently hysterical, half insane from sensory deprivation. Not every one is indulged to prowl free, defecating on other folks' lawns and reorganizing other folks' garbage, playfully snapping the necks of other folks' cats. A few dogs, worthy beasts, help blind people to cross streets. Several reportedly perform ranch chores. Dozens of canines in the U.S. alone fulfill a useful service as the quiet, well-behaved pets of old people and shut-ins. The rest, unfortunately, are as we know them. But dogs are a sensitive subject; some dog owners, like some tobacco smokers and most members of the Ku Klux Klan, tend to be passionately defensive about what they are pleased to think of as their own rights. Consequently you find two diametrically opposed and equally extremist points of view: on the one hand, that
all dogs are irredeemably noxious and should be banished, at least from our cities and suburbs, by enlightened legislation; and on the other hand, that some dogs are okay, at least some of the time. My own view is a moderate one that falls about halfway between these two.

Brothers and sisters, as the Lord is my witness: We got too many dogs.

A reliable estimate puts the total U.S. dog population at about sixty million, and that figure has risen by ten million over the past decade. Roughly five million are unclaimed strays held in animal shelters, awaiting adoption or execution, but meanwhile pet dogs are still breeding away. As I write this sentence there are six lunatic barkers within earshot (and one charming old mongrel with sad friendly eyes, next door, who maintains a monk-like silence). That's just too many. The situation is crazy. The dogs of America are—individually and demographically—out of control.

Of course we also have too many cats. Let no smug feliphile deny that. But there are a couple of important differences. First, cats are generally far quieter and less intrusive. They just don't have the vocal equipment, the heft, or the territorial instincts to assert themselves as conspicuously as dogs do. Second, when a human society has too many cats, it is mainly the cats who suffer. People drown them. Set them on fire for kicks. Hang them, in cute little nooses. Club them to death and toss the carcasses into the trash. Thereby achieving some sort of sorry equilibrium. It's less trouble that way, evidently, than exercising a modicum of foresight to get the females spayed and the males neutered. When a society has too many dogs, however, people and dogs both suffer. The extras (aside from those strays who end up in animal shelters) are not killed, but instead are given away or sold cheaply to persons who have no idea what a dog needs in terms of training and attention and sheer physical space, and who are not in a position to supply those things if they did know. Result:
miserable, desperate dogs who share out that misery generously to the humans all around them.

It wasn't always this bad. Dogs come from a noble lineage, a lineage full of intelligence and good character—they are closely related to wolves, after all. Many paleontologists even think that domestic dogs are directly derived from a small Asian subspecies known as
Canis lupes pallipes,
the Indian wolf. But the descent of the species
Canis familiaris
(to which all domestic breeds belong) is like a parable on the subject of bad company. They began losing their dignity about 10,000 years ago, when they first cozied up to humanity—the greased chute to degradation. We adopted them, we tamed them, we began breeding them selectively to our own sick tastes and mad purposes; we gave them squashed faces and curly tails and sawed-off legs, brain damage and hip dysplasia and hemophilia, permanent psychological infantilism; we generally brought out the worst in them. Among other particulars, we perfected the bark.

How did such sadomasochism ever start? Some people cherish a romantic belief that, in its earliest form, the dog-and-man association was a hunting partnership. According to this notion, our hunter-gatherer ancestors of the middle Stone Age reached an implicit understanding with certain canines to cooperate in the chase: The dogs were faster and better armed, the humans were smarter and more devious, both groups were social communicators, and the meat could be shared. But it's a fairy tale. No basis whatsoever in evidence. Reputable archaeologists guess, instead, that the dog's first role in civilization was to eat garbage.

Wild dogs were welcomed as scavengers, it seems, to the fringes of those nomad camps. The dogs cleaned up what would otherwise stink and draw flies. When a camp was moved they tagged along as walking garbage Disposalls. Tolerated, at a distance. Eventually they became familiar and permanent. Hunting and shepherding and sled-pulling and being coddled as pets all came later—not to mention their role as watchdogs.

For this last function they were outfitted with a new sort of voice. It was a voice lacking all modulation and felicity, but which carried and penetrated exceptionally well, with its sharp pulses of energy confined within an unwavering range of frequencies, its cough-like bursts of pure graceless noise—a voice offering the same musical quality as the sound of a pouting child whacking away at a cinder block with a cheap meat cleaver. The canine bark: one of mankind's first acts of genetic planning, and an enduring monument to our own fearful territoriality. Like the spear and the loin cloth, it might well have been useful in its day.