Scientists Explain How Giraffes Got Long Necks

Scientists have managed to sequence the genome of giraffes, and now have an explanation for their long necks.

The big surprise is that there were only a few mutations necessary to give the creature its distinctive physiology. Giraffes can reach up to 6 meters tall, and boast long graceful necks.

Giraffes have a very distinctive physiology

This huge neck means that giraffes have to pump blood a long way to their heads, and they have a large left ventricle in order to do so. Their blood pressure is around twice as high as other mammals.

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Scientists were not previously sure how the biology of giraffes evolved, and things were made more difficult given the lack of “intermediate” species to examine. The closest relative of giraffes is the okapi, which is more similar to a zebra.

To get a better idea of what was going on, scientists from Penn State University sequenced the genome of both the giraffe and the okapi. The full results of their work can be found in Nature Communications, and give a better idea of how giraffes evolved.

Genome sequencing yields fascinating results

The team, led by Douglas Cavener and Morris Agaba, isolated the gene-coding sequences of giraffes and found that just 70 genes were responsible for its physiology. Interestingly giraffes only diverged from okapi around 11-12 million years ago, and the two species are closely related.

Some of the unique genetic mutations are in fact responsible for multiple characteristics. For example there are a number of genes that control cardiovascular and skeletal development, and scientists believe that only a small number of genes were responsible for huge changes in both areas.

The team also uncovered clues as to how giraffes were able to evolve such long neck and necks which only have the same number of bones as those of other mammals, despite their length.

“To achieve their extraordinary length, giraffe cervical vertebrae and leg bones have evolved to be greatly extended,” said Cavener in a release. “At least two genes are required—one gene to specify the region of the skeleton to grow more and another gene to stimulate increased growth.”

Genes provide clues to evolution

One of the genes is known as FGFRL1, and it is particularly important in the early stages of embryo development. It also plays a role in rapid bone growth soon after birth.

FGFRL1 has been associated with cardiovascular and skeletal defects in humans when it does not express properly. This gene, along with 4 homeobox genes, are two elements which are needed for giraffes to evolve long necks and legs.

“What we think has occurred then, is the giraffe evolved a long neck, which occurred over roughly a 15 to 20 million year period, and as its neck extended out, its cardiovascular system was also changing in tandem—and that some of the same genes were actually controlling both processes in concert,” noted Cavener.

Scientists also found a group of genes related to metabolism and growth. These genes likely allow giraffes to eat acacia leaves and seed pods, which are toxic to lots of other mammals.

The next step for researchers is to fuse FGFRL1 into the mice genome in order to observe how growth is affected. It is hoped that this research could lead to treatment for humans who suffer from physiological ailments such as skeletal abnormalities.