The only thing that separates giraffes from their smaller cousins — besides a lot of vertical space — is a handful of genes.
Scientists have sequenced the giraffe genome for the first time, and they found that the genes responsible for the animals' long necks are also responsible for their unusually strong hearts.
Researchers compared giraffes to okapi, their closest relative, to spot the genetic quirks. More than half of the giraffe's specialized genes control development of its skeletal and cardiovascular systems.
In other words, a giraffe isn't just a stretched okapi. To evolve such a long neck, giraffes had to evolve better hearts, too.
A giraffe's blood pressure is twice as high as that of other mammals. Its heart has to be small and muscular to send blood 6 feet upward against gravity.
"As its neck extended out, its cardiovascular system was also changing in tandem. And some of the same genes were actually controlling both processes in concert," said Penn State's Douglas Cavener.
Researchers want to test some of those skeletal growth genes in mice. They're not expecting long-necked mice, but they're hoping to see changes in skeletal structure.
This video includes clips from The Cincinnati Zoo & Botanical Garden, the Detroit Zoo and Penn State University, and images from Getty Images, Doug Cavener and Radio Okapi / CC BY 2.0. Music provided courtesy of APM Music.