Scientists have long tried to figure out why giraffes have such long necks. Darwin believed it helped animals get to the tops of trees. Now there is a new theory about neck length that goes in a completely different direction. Was the famous evolutionary researcher wrong?
The extremely long neck of the giraffe is possibly a result of their violent fighting behavior. An international team of researchers concludes this from examining the fossil remains of an ancient giraffe. These animals probably hit their heads against each other during fights and subsequently developed a protective hood on their heads and extremely robust cervical vertebrae, as the scientists report in the journal “Science”.
The extreme necks of today’s giraffes could have developed in a similar way. They don’t bang their heads against each other, but their impressively long and muscular necks do.
“The common notion that the long necks only developed in the course of evolution because the animals used them to reach leaves in the upper part of the trees may not go far enough,” explains co-author Manuela Aiglstorfer from the Natural History Museum in Mainz and the State Collection for Natural History Rhineland-Palatinate. “Perhaps this is just a side effect and combat strategy is the primary reason for the development of the long neck.”
As a ruminant specialist, Aiglstorfer is part of Shi-Qi Wang’s team at the Chinese Academy of Sciences in Beijing. The researchers had examined the fossil remains of an animal that lived around 17 million years ago in what is now northern China: Discokeryx xiezhi, named after the Asian unicorn mythical creature Xiezhi. The analysis of the bones showed that it was a representative of the group of giraffes, explains Aiglstorfer. “This group was much more diverse then than it is today. For example, the animals had different skull appendages and also showed diverse fighting behavior.”
The investigations showed that Discokeryx had extremely thick and robust cervical vertebrae. This allowed the animals to absorb strong vibrations, as demonstrated by modelling. On their heads they wore a thick, disc-shaped structure, which in turn was probably provided with some kind of horn. Her neck wasn’t exceptionally long.
The researchers suspect that the animals rammed their heads against each other in a similar way to today’s ibex or musk oxen. Such fights could have occurred, for example, when courting a female. In fact, the vertebral structure of the primordial giraffe was more effectively adapted to the great force than is the case in modern animals that fight in this way, the researchers write.
Today’s giraffes live on the African continent. Despite the extremely long neck, around two meters long, their cervical spine consists of only seven vertebrae, as in most mammals. “The cervical vertebrae of modern giraffes are very different from those of Discokeryx, they are designed for length,” says Aiglstorfer.
Why animals developed such long necks in the course of evolution has occupied scientists for centuries. Some researchers assume that sexual selection drove the development: Males with a strong, long neck therefore won fights more often for the females and passed their genes on to the next generation.
The theory that advantages in acquiring food were more decisive and ultimately caused the neck to grow is better known: at the beginning of the 19th century, the evolutionary biologist Jean-Baptiste Lamarck suspected that the neck of a giraffe stretched over the course of its life because it always looked for the taller ones leaves stretched. According to Lamarck, the newly acquired property was passed on to the offspring. This theory has since been disproved because individual adaptations do not affect genes in this way. As we know today, these are the basis for the inheritance of physical characteristics.
The most common opinion today goes back to Charles Darwin, who, in accordance with his theory of evolution, assumed that individuals with a particularly long neck would arise by chance again and again. Since they can reach more food than their shorter-necked counterparts, they have better chances of survival and therefore more offspring to pass on the genetic basis for the long neck. In this way, an advantageous trait gradually asserts itself in a group of animals. “Our study did not show that there was no connection between neck length and diet,” says Aiglstorfer. “But we show that in ruminants there can also be other important influences that affect the structure of the cervical spine.”
