How Giraffes Evolved Such a Large Neck

When we think of animals with extreme adaptations, the giraffe definitely comes to mind. Along with other animal adaptations like the saber toothed cat’s teeth and the mantis shrimp’s strength, the giraffe has one of the most extreme evolutionary features; its neck. This animal has been the study of many scientists, all of whom are trying to discover why exactly this neck evolved.

In a well known but incorrect hypothesis Lamarck, a scientist that had hypothesized his ideas before Darwin, famously suggested that giraffes grew to have a large neck by stretching towards branches on trees. By continually doing this, they not only stretched their own necks to be longer but then passed the growth they received in life to their offspring, giving the progeny long necks as well. Once Darwin’s Origin of Species came out, the ideas of the time changed. The accepted theory on giraffe evolution is that the giraffes with the longest necks passed on their genes through natural selection, and that it took millions of years to get the animal we see now.

The two forces that drove giraffes towards elongating their necks are simple. The need to eat and the need to breed. Giraffes now are the tallest browsers by far in their habitats, and therefore can reach food no other animal can. This distinct advantage has helped females to choose males with longer and stronger necks. Males determine strength by quite literally hitting their necks against one another in battles termed “necking”. Often this can lead to severe injury or even death. Such risks have led only the most fit males to win the fights and thus selected to pass on their genes. This selection, among other factors, has led these animals to have necks that can reach 6 feet (1.8 meters) and weigh nearly 600 pounds (270 kg).

The evolutionary history of the giraffe brings us back to approximately 50 million years ago. An animal similar to antelopes evolved into two species that are extant today. Many of these animals roamed across Eurasia and Africa until they went extinct or evolved into animals we see today. These surviving members of the Giraffidae family are the okapi and the giraffe, both of which (Whom?) inhabit Africa. Many other extinct predecessors of the giraffe existed, and their fossils remain. By using these fossils scientists were able to figure out  how their necks evolved anatomically.

Giraffes, despite having such humongous necks, actually have the same number of neck vertebrae as a human. There are only seven vertebrae in mammal necks, meaning that the giraffe has vertebrae that are nearly a foot long each! Their cervical (neck) vertebrae have actually just extended in length, instead of adding more bones into the anatomy. This elongation is responsible for the neck becoming so long. If we compare vertebrae of the modern giraffe to its extinct ancestors we can begin to see when and where this elongation began to take place.

 

 

A recent study by Melida Donowitz and her team at the New York Institute of Technology College of Osteopathic Medicine closely looked at fossil specimens of giraffe ancestors, focusing especially on the cervical vertebrae and cranium (skulls) of all these animals. Surprisingly enough, it wasn’t just the vertebrae that were lengthening, but also the skulls. A new possible ancestor of the giraffe was also named, the Prodremotherium, which lived before the Giraffidae family came about. This Prodremotherium family had features very similar to those of the Giraffidae, as well as a known ancestor of the giraffes, called Canthumeryx. These two ancestral families both had the beginnings of the extreme neck lengthening that is seen in the modern Giraffidae.

The paper, published in the Royal Society Open Science, discussed several detailed aspects of each vertebrae in the neck that lengthened  over the 15 million years that the Giraffidae family existed and over the 50 million year time span of the ancestral evolution of long necks. Many species and families preceded the  Giraffidae family, all of which exhibited either neck or cranial lengthening.

 

 

Most scientists agree that, although unexpected, the cranium was actually the first part of the giraffe family to begin lengthening. It is difficult to pin down exactly when this started occurring, as fossils are few and far between, but within the relatively short time span of 15 million years, a neck the length of an entire human being developed. These amazing animals, and their evolutionary history can help us to understand not only more about them and their behaviors, but how evolution can rapidly change any animal is the correct pressures are implemented on them.