Home / Opinion / Views /  The enduring mystery of giraffe necks
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One morning recently, I was leaning on a lamp post. Not in case a certain little lady came by, but because a group of giraffes was there, about 10 metres away.

It was as if they were performing. They pranced, turned and nuzzled each other. Through it all, through dozens of photographs, I nursed the question I’ve always had about giraffes: why are their necks so long?

No other animal has a neck like that. Why giraffes?

One explanation seems obvious: they feed off the higher branches of trees and bushes. This means no competition, because no other animal has a neck tall enough to reach those heights. In other words, competition from other mammals has driven the evolution of a long neck. Since Darwin first proposed his Theory of Evolution, this is how most biologists have explained the giraffe’s neck.

But over time, researchers started questioning this theory of competition. In 1996, for example, Rob Simmons and Lue Scheepers of the University of Cape Town wrote: “In searching for present-day evidence for the maintenance of the long neck, we find that during the dry season (when feeding competition should be most intense) giraffes generally feed from low shrubs, not tall trees." In fact, female giraffes generally feed with their necks stretched horizontally—not reaching for the tops of trees. Besides, both females and males “feed faster and more often with their necks bent"—not stretched upright. 

“Long necks," Simmons and Scheepers concluded, “did not evolve specifically for feeding at higher levels."

Well, what did they evolve for? The authors had an intriguing hypothesis: long necks are sexually selected. Male giraffes are known to battle each other: they position themselves side-by-side, jostling and pushing. Then they hit out “with [their] well-armored heads on long necks". Remember that giraffes have small but hard horns on their heads. So, each combatant will actually try to hit the other’s body with his horns. To that end, the longer his neck, the more easily a giraffe can strike hard at his opponent’s soft spots.

Weaker males are injured and often killed in these fights; the survivors are those with longer, thicker necks. These are the animals that become dominant and have the females to themselves. In other words, these are the animals that will pass on their particular genes. This is the charmingly-named “necks-for-sex" hypothesis for long necks on giraffes.

This mechanism of sexual selection, write Simmons and Scheepers, “provides a better explanation [for the long neck] than one of natural selection via feeding competition."

One issue here, though, is that female giraffes don’t fight. So, this sexual selection theory rests on the assumption that males must invest (speaking biologically, of course) in growing their necks more than females do. Yet, female giraffes also have long necks. In fact, lay giraffe watchers like me cannot decide the gender of giraffes going solely by the lengths of their necks. Which may be why wildlife biologists began questioning this theory as well.

Three of them, for example, examined 17 male and 21 female giraffes. They measured not just neck lengths but leg lengths, the ratio of neck length to leg length, the weights of the heads and necks, and the overall body weight.

The results were a revelation. Between a male and a female of about the same body weight, there were “no significant differences in any of these dimensions." Now, it is true that adult males are much heavier than females—with heavier heads and necks—but even so, their necks are no longer than the females’ necks. Mincing no words, the scientists titled the paper they published thus: “Sexual selection is not the origin of a long neck in giraffes" 

Incidentally, the same three biologists also found a different way to show that the Darwinian feeding competition theory didn’t hold either. In 2008, they studied the remains of 26 giraffes that had died because of a drought in Zimbabwe. The really young ones had died because they could not compete with the others. The tallest and heaviest males had died because the drought meant they couldn’t find enough to eat anyway. “Thus, the survivors of this drought were young adults," Mitchell and colleagues wrote, “a finding contrary to the predictions of Darwin’s feeding hypothesis." 

So really, and all over again, how did giraffes get their long necks?

The 1996 discovery in China of a fossil of an ancient giraffe-like animal, Discokeryx xiezhi, and the quarter-century of research it led to, prompted a new twist in this story. In a recent paper, a team of scientists report that the creature had a 5 cm thick helmet-like growth on its head. It also had thickened vertebrae “and the most complicated head-neck joints in mammals known to date". Taken as a whole, the remains suggest an animal “adapted for a fierce intermale head-butting behaviour". They fought like this both to compete for and to impress females of the species, as possible mates. (Sexual selection promotes giraffoid head-neck evolution and ecological adaptation, Shi-Qi Wang et al, Science, 3 June 2022).

And as the species and its fighting style evolved, the necks grew longer, too. Though there are questions to ask there as well. Other animals such as goats, deer and antelopes also fight with their necks and heads—or the horns on their heads—and they haven’t developed long necks. Why not?

Still, Wang’s team believes their Discokeryx xiezhi fossils show that sexual selection was indeed a factor in the lengthening of giraffe necks. But they believe that foraging was also a factor. As Wang told a journalist: “Maybe the profound purpose for the long neck is to reach food at the higher levels, but the direct driving force...may be fighting because males fight using their long necks." I suspect it will be a long (pun intended) time before we hear the last word on this.

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. His Twitter handle is @DeathEndsFun

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