Scientists have uncovered information about the giraffe's unique long neck by sequencing its genome along with that of its closest living relative, the okapi of the African rain forest.
"The giraffe's stature, dominated by its long neck and legs and an overall height that can reach 19 feet (approximately 6 meters), is an extraordinary feat of evolution that has inspired awe and wonder for at least 8,000 years - as far back as the famous rock carvings at Dabous in the Republic of Niger," said Douglas Cavener of Penn State University and senior author of the study.
"The evolutionary changes required to build the giraffe's imposing structure and to equip it with the necessary modifications for its high-speed sprinting and powerful cardiovascular functions have remained a source of scientific mystery since the 1800s, when Charles Darwin first puzzled over the giraffe's evolutionary origins," he added.
Cavener and his team examined the gene-coding sequences of the giraffe and okapi and compared them to more than 40 other mammals including sheep, goats, cows and humans. Although the okapi possesses similar gene sequences, they look more like a zebra. The similarities and differences between them were used to gauge the unique genetic changes in the giraffe.
The Penn State team used various comparative tests to gain deeper insight into the genome sequences of the giraffe and the okapi and discovered 70 genes that showed signs of adaptation.
"These adaptations include unique amino-acid-sequence substitutions that are predicted to alter protein function, protein-sequence divergence, and positive natural selection," Cavener said
More than half of these genes are for proteins that are responsible for the regulation of the development and physiology of the skeletal, cardiovascular and nervous system, all of which would be needed to give the giraffe its unique long neck and physical characteristics.
"We hope that the publication of the giraffe genome and clues to its unique biology will draw attention to this species in light of the recent precipitous decline in giraffe populations," Cavener said. "While the plight of the elephant - giraffe's shorter companion in the African savannah - has received the lion's share of attention, giraffe populations have declined by 40 percent over the past 15 years due to poaching and habitat loss. At this rate of decline, the number of giraffes in the wild will fall below 10,000 by the end of this century. Some giraffe subspecies already are teetering on the edge of extinction."
The findings were published in the May 17 issue of Nature Communications.
