Whether your summer plans include a trip to the African Serengeti or just a day at the zoo, take note of the giraffes. The tallest of mammals, their legs alone measure more than many humans—six feet—and they can run up to 35 miles an hour, according to National Geographic.

But how did the giraffe get so tall, and what’s with that long neck? A new study offers some clues.

Researchers from Pennsylvania State University and the Nelson Mandela African Institute for Science and Technology in Tanzania have sequenced the genomes of the giraffe and its closest living relative, the okapi of the African rainforest. The study identified the genetic changes that resulted in the evolution of the giraffe's exceptionally long neck and its rank as the world's tallest land species.

The study was published in Nature Communications on May 17.

To identify genetic changes likely to be responsible for the giraffe's unique characteristics, the researchers compared the gene-coding sequences of the giraffe and the okapi—both originated from the same ancestor 11 to 12 million years ago—to more than forty other mammals including the cow, sheep, goat, camel, and human.

Using a battery of comparative tests to study the genome sequences of the giraffe and the okapi, the scientists discovered 70 genes that showed multiple signs of adaptations.

Over half of the 70 genes code for proteins that are known to regulate development and physiology of the skeletal, cardiovascular, and nervous system are also the type of genes predicted to be necessary for driving the development of the giraffe's unique characteristics.

Of those, some show multiple signs of adaptation in the giraffe, suggesting that the giraffe's stature and turbocharged cardiovascular system evolved in concert through changes in a small number of genes.