August 5 For no reason I can put my finger on apart from laziness, I didn't send out a number of my columns in April/May/June. Maybe nobody missed them, maybe not. For what it's worth, I'll occasionally email one of those.
Like this one, which is about the necks of giraffes. Why are they so long? I bet that's a question plenty of you have asked at some point. Naturally, some scientists have also asked it, and there are theories that seek to explain the length. I don't think "necking" is one of those theories. If that interests you ... My column on June 17 examines those theories. Take a look: The enduring mystery of giraffe necks, https://www.livemint.com/opinion/online-views/the-enduring-mystery-of-giraffe-necks-11655399136363.html And let me know what you think. cheers, dilip --- The enduring mystery of giraffe necks One morning some weeks ago, I was leaning on a lamp post. Not in case a certain little lady came by, but to photograph a group of giraffes not more than about 10 or 20 metres away. It was as if they were performing for us. They pranced and turned, scratched themselves on a tree trunk and nuzzled each other. Through it all, through the dozens of photographs I got, I nursed the same 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 to any giraffe-watcher: they get their food from heights - the higher branches of trees and bushes - and thus need to be tall. Besides, they can feed without bothering about competition, because no other animal has a neck tall enough to reach those dizzying heights. In other words, competition from other hungry mammals has driven the evolution of a long neck. Since Darwin first proposed his Theory of Evolution, this is how the majority of biologists have explained the giraffe's neck. Is this a valid, reasonable theory? Well, the best thing about writing this column is finding that there are scientists who have searched for answers to nearly every question you might think of about the world around us, and then reading about the results of those searches. Theories emerge, they are tested, evolve, get rejected or confirmed, and that process itself is riveting. So it is with giraffes and their necks. Indeed, over time, giraffe researchers started questioning this theory of competition. In 1996, for example, Rob Simmons and Lue Scheepers of the University of Cape Town wrote this in a paper: "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) giraffe generally feed from low shrubs, not tall trees." In fact, they reported that more often than not, female giraffes feed with their necks stretched horizontally - not reaching up to the tops of trees. What's more, both females and males "feed faster and more often with their necks bent" - not stretched upright. ("Winning by a Neck: Sexual Selection in the Evolution of Giraffe", The American Naturalist, November 1996, https://www.journals.uchicago.edu/doi/10.1086/285955.) So much for competition and reaching for food at heights. "Long necks," Simmons and Scheepers concluded, "did not evolve specifically for feeding at higher levels." Well, then what did they evolve for? The authors proposed a quite different and most intriguing hypothesis: long necks are sexually selected. After all, male giraffes are known to battle each other to gain access to females and for dominance in their groups. How do they do this? 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 swing his horns vigorously into the other's body. 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 ones that survive 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 tend to 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" (G Mitchell, SJ Van Sittert and JD Skinner, Journal of Zoology, August 2009, https://zslpublications.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-7998.2009.00573.x ). 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." ("The demography of giraffe deaths in a drought", Transactions of the Royal Society of South Africa, March 2010, https://www.tandfonline.com/doi/abs/10.1080/0035919X.2010.509153). 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 like 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. -- My book with Joy Ma: "The Deoliwallahs" Twitter: @DeathEndsFun Death Ends Fun: http://dcubed.blogspot.com -- You received this message because you are subscribed to the Google Groups "Dilip's essays" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/dilips-essays/CAEiMe8qYkDztZj2t0XWhLYhff90B0_wZH-4rPPZ4EgoFP6AkuQ%40mail.gmail.com.
