Neck and neck Anup Shah/Getty

Tweaking a few dozen key genes that regulate development gave giraffes their long necks. It’s a discovery that points to the subtle complexity behind this striking adaptation.

Biologists now routinely compare genomes of related species to identify the genes that may underpin their differences. Douglas Cavener of Penn State University in University Park, Pennsylvania, realised that giraffes afforded an unusual opportunity because their closest relative, the okapi, lacks the giraffe’s elongated body.

Cavener and his team sequenced the genomes of both species and identified 70 genes where the giraffe version showed clusters of unique changes or other signs of natural selection.


When the researchers looked more closely, they found that 46 of these genes were involved in regulating the development of the skeleton, cardiovascular system or nervous system. This fits giraffes’ unusual biology: long necks and legs require unusual bone growth, and their great height requires specialised changes in the heart, blood vessels and nerves.

“That was really remarkable,” says Cavener. Similar studies of unique genetic changes in other mammals typically turn up no more than one or two developmental genes, he notes.

Moreover, some of the altered genes affect precisely those body regions where giraffes are unique. The gene FGFRL1, for example, has been shown to affect development of the neck in mice, and the giraffe version has mutations that affect its action.

Cavener’s study provides an unusually detailed look at the evolution of body form. “It reveals the complexity of the evolutionary process that resulted in the modern giraffe,” says Oliver Ryder, a geneticist at the San Diego Zoo Institute for Conservation Research.

Cavener has not yet proven that the genes he has identified are actually responsible for the giraffe’s body form. However, he is now working to insert the giraffe versions of these genes into mice to see how each gene alters their development.

Last year, researchers showed what an intermediate stage between an okapi and a giraffe may have looked like. They did so by analysing bones from Samotherium major, a prehistoric relative of the giraffe that lived in parts of Eurasia some 7 million years ago. It had a neck about 1 metre long, compared with the giraffe’s 2.6 metres.

Though this extinct animal was probably not a direct ancestors of giraffes, it does show a lengthening of the neck compared with that of a short-necked precursor — a sort of an intermediate state.

Journal reference: Nature Communications, DOI: 10.1038/ncomms11519

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