The surprising reason why giraffes have such long legs

A long neck has advantages, but also a high cost: the enormous energy that the heart has to pump to the brain. In a new study, researchers invented an “elafa” — and discovered that giraffes’ hearts have an unexpected ally: their long, long legs.

If you’ve ever wondered why the giraffe has such a long neck, the answer seems obvious: Allows you to reach the succulent leaves at the top of tall African acacia trees.

Only giraffes have access straight to those leaves, while smaller mammals compete with each other on the ground. This exclusive food source appears to allow giraffes to reproduce throughout the year and withstand droughts better than smaller species.

But the long neck has a high price. The giraffe’s heart has to generate enough pressure to pump blood several meters up to the head. THE blood pressure of an adult giraffe usually exceeds 200 mm Hg — more than double that recorded in most mammals.

As a consequence, the heart of a giraffe at rest consumes more energy than the entire body of a human being at rest, and more energy than the heart of any other mammal of similar size.

However, according to a new report published in Journal of Experimental Biology, the giraffe’s heart has some helpers until now underestimated in their fight against gravity: your long, long legs.

Meet the “elafa”

In the new study, Roger S. Seymourresearcher at the University of Adelaide, Australia, and Edward Snellingfrom the University of Pretoria, in South Africa, quantified the energy cost of pumping blood on a giraffe and compared it with that of a imaginary, short-legged animal but with a longer neck, enough to reach the same height as the treetops.

This creature was a kind of “Frankenstein-like” combination: the body of a eland (also called papacala)a common African antelope, and the neck of a giraffe, explain Seymour and Snelling in an article in .

The two researchers, who gave the imaginary creature the name “Elafa“, that this animal would use an impressive 21% of your total energy just making the heart work, in compared to 16% in a giraffe and 6.7% in a human being.

By raising its heart closer to its head thanks to its long legs, the giraffe “saves” around 5% of energy that you get from food. Over the course of a year, this energy saving would be equivalent to more than 1.5 tons of food — enough to make the difference between life and death in the African savannah.

How giraffes work

In his book, the zoologist Graham Mitchell reveals that the ancestors of giraffes they already had long legs before they develop long necks.

Isto faz sense from an energetic point of view: long legs make the work of the heart easier, while long necks make it difficult.

Although, the evolution of long legs also brought costs. Giraffes are forced to spread the front paws too far apart to drink water, which makes them slow and clumsy to rise and flee if a predator appears.

Statistics show that giraffes are the prey mammals most likely to leaving a drinking fountain without even drinking.

How long can a neck be?

O energy cost of the heart increases directly in proportion to the height of the neck — which imposes a natural limit. A sauropod dinosaur, the Giraffatitanrises 13 meters above the ground in Berlin’s Natural History Museum. But the living creature You could hardly lift your head at this point.

Its neck, measuring 8.5 meters high, would require a blood pressure of around 770 mm Hg to get blood to the head — almost eight times more than that observed in the average mammal. This is unlikely, as the energy cost of pumping the blood would be greater than that spent by the rest of the entire body.

sauropod dinosaurs They couldn’t lift their heads that much without fainting.. In fact, say Seymour and Snelling, it is unlikely that any land animal in history has surpassed the height of an adult male giraffe.