Why did the giraffe get its long neck?

• Enjoyyourlife
• Thứ Tư, 31 tháng 8, 2016
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If we are talking about height, no animal can beat the giraffe! With an astonishingly long neck, a giraffe can be more than 18 feet tall, making it the world's tallest animal. It is also one of the world's heaviest animals - a male giraffe may weigh up to 4,200 pounds!

Unique genes that affect the skeleton, heart and nervous system may explain how the giraffe evolved into the world's tallest land animal, researchers have revealed.

Scientists now have the genetic instruction book that contains all the secrets of the giraffe, which over the past 12 million years has developed into one of the most bizarre creatures on Earth.

Mapping the giraffe's genetic code, or genome, has highlighted a host of DNA sequences that make the long-necked animal so special.

Standing up to 19ft (six metres) tall, the giraffe's peculiar body is dominated by its stretched out legs and neck.

Professor Douglas Cavener, from Pennsylvania State University in the US, who led the new study, said: "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."

The animal's heart, built to pump blood vertically a distance of two metres (6.5ft) to its brain, has an unusually large left ventricle chamber.

Taking a giraffe's blood pressure would show a reading twice as high as that of other mammals.

The giraffe can also sprint at speeds of up to 37 mph on its long spindly legs, and despite appearances its neck contains the same number of bones as seen in other mammals, including humans. The big difference is that both the giraffe's leg and neck bones are greatly extended.

The scientists pinpointed unique regions of the genome by comparing it with that of the giraffe's close relative, the okapi.

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Both animals have a common ancestor but branched off in separate directions along the evolutionary path around 11 to 12 million years ago.

A battery of tests comparing the two animals uncovered 70 giraffe genes that showed multiple signs of adaptation. More than half of these coded for proteins known to regulate the development of the skeletal, cardiovascular and nervous system.

Several genes controlled both heart and artery and skeletal development - raising the intriguing possibility that the giraffe's stature and cardiovascular system were modified together through changes to a small group of multi-purpose genes.

One key gene is thought to be FGFRL1, which regulates a biological pathway critical to bone growth. In addition, four "homeobox" genes were identified that are known to specify the regions of the spine and legs.

"The combination of changes in these homeobox genes and the FGFRL1 gene might provide two of the required ingredients for the evolution of the giraffe's long neck and legs," said Prof Cavener.

Undoubtedly, giraffes take full advantage of their height. When they are hungry, they don't have to lower their necks to eat grass or stand on their toes to reach for leaves. All they need to do is to stand near a tree and have an all-you-can-eat buffet of leaves and twigs from the tops of trees. Since giraffes are so tall, they don't have to compete with other plant-eating animals (such as zebras and antelopes) that also live in African savannahs. Their remarkable height also helps to keep them out of danger, as they can spot hungry lions or hyenas from far away.

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