How the Giraffe Got Its Neck

It’s difficult to know what to make of the giraffe. It shuffles like a camel (right legs forward, then left legs) but runs like a rabbit (hind legs forward, then front legs). Its distinctive aroma repulses many ticks but enchants certain people. It bellows, hisses, and moans in the wild, and in captivity it hums in the dark. It naps with its head aloft but sleeps like a swan, with its head on its haunches. Had Aristotle ever seen a giraffe, he might have said that it was the product of an interspecies dalliance at the watering hole, which he thought of as a kind of zoological swingers’ club—a place where “bastard animals are born to heterogeneous pairs.” Centuries of further guesswork failed to clarify the giraffe’s essential nature. Simone Sigoli, a Renaissance traveller, wrote that it had the body of an ostrich, only with fine white wool instead of feathers, and that it ate bread. “It is quite a deformed thing to see,” he concluded. Sigoli’s contemporary Sir John Mandeville (likely the pseudonym of a travel-averse plagiarist) described the “gerfaunts” of Arabia as deer-rumped horses. For the eunuch general Zheng He, who brought a giraffe home to Beijing, in 1415, it was a mythical qílín incarnate. Not until the seventeenth century did the English, who fixated on the giraffe’s camel-ish shape and leopard-ish coloring, stop calling it a camelopard. Today, of course, we recognize the giraffe as a distinct species, though the misapprehensions of the past endure in the animal’s Linnaean name: Giraffa camelopardalis.

And then there’s that neck. Why is it so long? Unlike the swan and the ostrich, which have a surplus of neck bones, the giraffe has seven cervical vertebrae, the standard count for a mammal. But each one is eleven inches in length. A human’s entire spine, by comparison, is about two feet from top to bottom, not much longer than a giraffe’s tongue. (Fynes Moryson, a Scotsman who went to Constantinople in 1597, was distressed to find that the giraffe in the palace menagerie there was able to plant “familiar kisses” on him from great range.) The French naturalist Jean-Baptiste Lamarck held that a giraffe was merely an antelope whose progenitors had strained their necks toward higher and higher branches for food. Charles Darwin gave barely a thought to the neck problem—it didn’t appear in his magnum opus, “On the Origin of Species,” until the sixth edition—but he favored a similar, if more scientifically rigorous, explanation. In periods of drought, he suggested, when all the other animals on the savannah were scrounging at eye level, Giraffa sprouted the evolutionary equivalent of an EZ Reacher, which gave it access to a private larder in the succulent crowns of the acacia trees, a privilege it passed on to its offspring. “It seems to me almost certain that an ordinary hoofed quadruped might be converted into a giraffe,” Darwin wrote, echoing Lamarck. The theory was accepted as gospel for decades, until researchers noticed two problems. First, no other quadrupeds underwent such a conversion: the giraffe remained the lankiest thing around. And second, the animal grazed with its neck horizontal about half the time, feeding on the same bushes and shrubs as everyone else. (As Edgar Williams notes in his book “Giraffe,” the animal is a born topiarist, “giving a manicured appearance to the savannah.”)

Another popular theory involved sexual selection. To establish social dominance, male giraffes engage in a practice known as necking, swinging their heads at each other and trying to score a hit with their ossicones, the horn-like growths on their skulls. (Afterward they make up, sometimes quite bawdily.) For the neck to be a primarily sexual characteristic, it would need to be larger in males than in females, like a fiddler crab’s fiddle claw—but it isn’t. Although males are indeed taller and heavier than females, the sexes’ necks are proportional. Yet another theory, less widely accepted than the first two, posits that the giraffe’s long neck is compensation for its long legs. (You try bending down to drink on those things.) The neck’s true provenance is perhaps some combination of these theories. As Darwin wrote, “The preservation of each species can rarely be determined by any one advantage, but by the union of all, great and small.”

A new paper, published today in the journal Nature Communications, addresses the issue from a genetic perspective. The lead authors of the study—Morris Agaba, of the Nelson Mandela African Institute for Science and Technology, in Tanzania; and Douglas Cavener, of Pennsylvania State University—seem less interested in why the giraffe’s neck is so long than in how and when it got that way, a question they investigate by comparing the giraffe’s genome to that of its closest living relative, the okapi. At first glance, the family resemblance is easy to miss. Okapis dwell in the lush equatorial forests of the Congo, and were not discovered by Western zoologists until the Victorian era. They are normal-necked and about the size of a small horse, with the coloring of a chocolate Labrador on top and zebrine stripes around their legs. And yet nearly a fifth of the proteins that their genes encode are identical to those of giraffes. (Another similarity: both animals are cloven-hoofed cud-chewers, which makes their meat kosher.) Agaba, Cavener, and their colleagues estimate that the two species diverged about eleven and a half million years ago, fairly recently on the evolutionary time scale. By cross-referencing the animals’ genomes, the researchers were able to focus on seventy giraffe genes that show unique signs of adaptation. Fully two-thirds of these DNA snippets control aspects of development and physiology.

Consider, for a moment, the biomechanical quandaries involved in being a giraffe. To get blood from your heart to your brain, a vertical distance of at least six feet, requires blood pressure two and a half times higher than a human’s. Every time you bend down for a drink, spreading your front legs a little in order to get lower, the blood rushes to your head and you risk stroke. Every time you straighten up, the blood rushes back and you risk fainting. And when you’re standing, gravity causes fluid to pool in your lower extremities, which makes them swell. The giraffe manages these handicaps with a suite of anatomical innovations. Its heart is “turbocharged,” according to Agaba and Cavener, small in proportion to the animal’s over-all size but with tremendously thick walls. The veins, arteries, and capillaries are rugged, too, behaving as a kind of dampening system to prevent the blood from sloshing around willy-nilly. And the giraffe’s skin, tough and tight-fitting, performs the same task as a compression stocking. (The Victorian explorer Henry Stanley had to melt down his zinc canteens to make bullets hard enough to penetrate the giraffe’s hide.) The adaptations are also neurological. A giraffe’s left laryngeal nerve, for instance, which controls the muscles in its voice box, must wind some fifteen feet through the neck, even though the distance between the brain and larynx is only about six inches as the crow flies. And, if the prospect of swallowing food down such a long neck is startling, recall that giraffes are ruminants, and that whatever goes down must also come up. Their esophageal muscles are correspondingly strong.

The seventy genes that Agaba and Cavener’s group examined doubtless play a role in many of these adaptations, regulating which regions of the embryonic giraffe’s skeleton expand and how much, and instructing the developing vascular and nervous systems how to compensate. In fact, the paper’s authors suggest that the giraffe’s stature and its physiology may have co-evolved, with each growth spurt accompanied by, say, sturdier blood vessels or thicker skin. The team is unveiling a new initiative, the Giraffe Genome Project, to continue their inquiries. In the meantime, the camel-like, rabbit-like, swan-like, ostrich-like giraffe will remain one of nature’s curiosities, its neck swaying faintly as it shuffles across the savannah.

  • Anthony Lydgate is the editor of Elements,’s science-and-tech blog.

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