EVOLUTIONARY
BIOLOGY
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157
Scientists could go further in their predictions about molecular genealogy. Sure, we're genetically closer to mice than to flies, but how can it be that nearly half of our DNA still resembles the recipe for a creature with compound eyes, backward-bending legs, and a persistent desire to take up residence in a Porta-John? For that matter, we share one-fifth of our genetic code with yeast, an organism that has neither cabeza, abdomen, nor anything else requiring multicellularity. What sorts of genes could possibly be tying us to fungus? As it happens, there are many basic chores that every cell must know how to do. Whether of wildebeest, baker's yeast, human humérus, or fly glomerulus, a cell must be able to take in nutrients, throw out the trash, stay in shape, and divide when told. One would predict, then, that the genes encrypting such fundamental tasks would be the genes least likely to change over evolutionary time, no matter who inherits them — and that is precisely what geneticists have found. The cell's maintenance and division genes are among the most well preserved specimens nature has to offer. We should all look, after half a billion years of evolutionary heaving and hawing, as dewily unchanged as do the genetic instructions that tell a cell to split in two. In fact, science has put the timelessness of DNA's blue-collar codes to spectacular use. Through studying the genes in yeast that oversee cell division, researchers have learned far more about human cancer than the malignancies themselves would deign to divulge. Tumor cells are ugly, messy, hard to handle. Yeast cells are pliable and generous (remember, they gave us wine). Should we ever declare victory in the ragged "war on cancer," the theory of evolution can claim credit for having sharpened the spears. Another reason evolutionary theory may sometimes seem less bedrock-solid than it is stems from some of the internecine haggling among evolutionary biologists over details — the sort of squabbles that for almost any other scientific discipline would be of interest only to the contestants and their listservs; but with Darwinism as the national blood sport, everybody wants to be cc'd. Evolutionary biologists do argue over the mechanics of evolutionary change, how fast it happens, how to measure the rate of evolutionary change, whether transformations occur gradually and cumulatively, putter and futz, generation after generation, always working to stay ahead by a nose, until, whaddya know, you're wearing a Chiquita on your beak; or whether long banks of time will pass with nothing much happening, most species maintaining themselves in a comfortable stasis until a crisis strikes — an asteroid hits the Earth, or volcanoes dress the skies in flannel pajamas of