Reaching high-up food may not have been the only or even main reason giraffes evolved to have long necks, as new research suggests that these extended body parts help the animals keep cool in the hot African savannah.
"There have been at least six explanations for the evolution of their shape," zoologists wrote about the giraffe's iconic necks in a study to be published in next month's issue of the Journal of Arid Environments. Giraffes slowly began developing their lengthy necks starting more than 16 million years ago. And this unusual morphology has captivated and puzzled people since ancient times.
Jean-Baptiste Lamarck was the among the first scientists to tackle the question of how the giraffe got its long neck, theorizing that they came about because the mammals had to constantly reach for food, thus causing them to permanently stretch out their necks over each animal's lifetime. But naturalists Charles Darwin and Alfred Russel Wallace challenged Lamarck's ideas, suggesting that the necks are a result of natural selection—giraffes with the longest necks were the ones that thrived and produced offspring because they had the greatest access to food.
But that wasn't the end of the story. Other scientists have suggested over the years that the necks provide male giraffes with a club that they can use to fight other creatures. Perhaps the necks give them a better vantage point to spot predators or the necks could help compensate for the giraffe's long legs, allowing them to drink water while keeping their bodies out of harm's way, reports Nature.com. In the latest study, researchers considered one reason proposed in 1963: heat.
Retaining or avoiding heat is a major driving factor in the evolution of many warm-blooded animals, including humans. The hominids who first evolved in Africa were notable for their tall, lean physiques with extended limbs. These body types have more surface area on the torso and arms and legs to radiate heat, helping them stay cool in the Africa's hot ecosystems.
To calculate whether this could be a factor for giraffes, researchers first had to measure the surface area of the animals, which is a lot more challenging than calculating the surface area of a cylinder. Using data from 60 of the animals, they divided their bodies into four sections and measured them out individually before combining them into a whole giraffe, reports Ryan Mandelbaum for Gizmodo.
It turned out that despite their long necks, giraffes don't have that much more skin surface area than other large animals, because their torsos are relatively small for their size. This means that that the giraffes don't inherently have any advantage in radiating heat off their bodies, Nature.com reports.
However, those necks can serve as a cooling advantage when deployed in a certain way. If a giraffe faces the sun, as they have been observed to do during the day, the long, thin neck keeps a lot of the animal's skin in shadow compared to shorter, stouter animals, leaving only a relatively small torso to be pounded by the rays of the sun.
"Our analysis here suggests that the thermoregulatory advantages that flow from [this] shape are significant and in our view may have supplemented, or been a component of, the selection pressures that resulted in the shape of giraffes," the authors conclude.