A Puzzle in Zoology

A Puzzle in Zoology

Isn’t it strange how animals vary in their natural defenses? Some are poisonous, some have armor, some have horns, some have thick skin, some have spikes, some have tough scales, some live in shells, some just taste bad; but some—many—have none of the above. Some can only run and hide. The llama, say, has none of these weapons: it lags behind in the arms race against its predators. Why doesn’t it have a formidable horn, or an armored body, or spikes? Why aren’t more prey animals poisonous? Evolution has had a long time to hone the animal against its natural enemies; you would think natural selection would have favored defensive weapons of the kind we see in other animals. Why aren’t genes for armor and spikes more common? The human animal seems particularly vulnerable, and we are evolutionarily advanced. Our skin is thin and exposed, easily cut; we bleed easily. We have no natural armor or a thick hide or pointy appendages; we have to make these things ourselves. Isn’t it obvious that they would be a good idea survival-wise? Natural selection seems to have been asleep on the job. We are nowhere near as well-protected as an armadillo (also a mammal). We are asking for trouble, as are many animals. You might say it’s a trade-off: we lack these assets but we have others that make up for the selective disadvantage. You can’t run fast, say, if you are heavily armored (think of tortoises). But that seems unconvincing: many better protected animals do a lot better at escaping predators (or did in the old days), and a thicker skin doesn’t seem to have much of a downside. Antelopes would do better if they had spikes on their throat, like a porcupine, or a tooth-resistant hide in the most dangerous parts. Why aren’t all animals armed to the hilt? Millions of years of evolution, with survival depending on it, and that’s the best the genes can come up with! I could design a much tougher antelope myself and yet evolution has left it extremely vulnerable (especially in the throat area). Why must it resort to running away? It needs the biological equivalent of a knife or a gun; then it could stand its ground. We humans have done extraordinarily well by inventing technology to make up for our defensive (and aggressive) deficits, so why hasn’t evolution done the same by means of natural selection? It’s not rocket science. It has the know-how, as better protected animals attest, but it lacks the will—why? Why aren’t all animals more like the armadillo? We wouldn’t be at all surprised if we came upon a planet populated by heavily armed armadillo-like creatures.

And why do some animals live so much longer than others? It isn’t that long life is biologically impossible—just look at turtles, lobsters, sea sponges, and Greenland sharks (400 years!). A longer life means more mating opportunities, which means more offspring, which means more genes in the gene pool. The selfish gene is all in favor of long life, so why is it confined to a minority of species? The selective pressure to live long (and prosper) is strong and yet few animals achieve it. If some can, why not more? If some sea sponges can live for thousands of years, why can’t brainier organisms do the same? There is nothing about biological tissue that condemns it to a brief life—in principle, it could go on indefinitely. And yet most animals have short life spans (comparatively speaking). Is there some law of nature that allows rocks to exist forever but not rats? Apparently not (entropy applies to everything). So: why is life on earth generally short? Why do some creatures live longer than others? Why does death come sooner for some? If there were a divine creator, we would ask why he decided to impose this unjust inequality on life—it seems arbitrary, anomalous. The tortoise, say, is well-armed and long-lived, unlike the rabbit or the deer. If nature can do the one, why not the other? Why aren’t there more genes for longevity and a strong coat of armor? That would seem the natural direction for evolution to take, but it hasn’t taken it. Puzzling.[1]

[1] I don’t recall seeing these questions discussed, but surely, they must have been. The answer is certainly not obvious. It’s no use saying that some animals are just naturally more aggressive than others, or that some are naturally fitter and sturdier. The question is why.