The Giraffe Neck Evolved for Sexual Combat
If you’re a fan of Rudyard Kipling’s Just So Stories, you’ll recall “How The Elephant Got His Trunk,” “How The Leopard Got His Spots,” and the like. You probably also remember from basic biology the regnant evolutionary account of “How The Giraffe Got His Long Neck.” It lent itself to contrasting Lamarckian selection—in which early giraffes stretched their necks to reach higher leaves, thereby bequeathing their long neckedness to subsequent generations—with Darwinian natural selection, in which evolution favored those individual giraffes whose genetic background endowed them with longer necks, thus selecting for this trait. Although Lamarck remains in disfavor, research recently published in the journal Science strongly suggests that a different and far sexier variant of natural selection—appropriately termed sexual selection—has been operating.1
Time to revise the textbooks.
But not completely. It remains true that giraffes with longer necks get to munch on leaves that are beyond the reach of other, shorter-necked competitors. Also true is that the highest leaves tend to be more nutritious. Food matters: Without enough of it, living things—however well adapted in other ways—wouldn’t survive to project their genes into the future. Looking at giraffes (and who doesn’t like to do that?), it’s all too easy to see them as merely munching machines on stilts, although their extraordinary anatomy necessitates a number of evolutionarily expensive adjustments, such as providing sufficient blood flow to that skyscraper head,