Researchers modeled a fictional chimera called the elaffe (a giraffe neck on a short eland body) and found its circulatory demands would be dangerously high. The study reports the elaffe would spend about 21% of its energy on circulation versus about 16% in real giraffes and 7% in humans. Longer legs save roughly 5% of cardiac energy — more than 3,300 pounds of food annually — and giraffes also evolved highly elastic blood vessels to manage extreme blood pressures.
Why Giraffes Have Such Long Legs — A Heart-Driven Evolutionary Trade-off
Researchers modeled a fictional chimera called the elaffe (a giraffe neck on a short eland body) and found its circulatory demands would be dangerously high. The study reports the elaffe would spend about 21% of its energy on circulation versus about 16% in real giraffes and 7% in humans. Longer legs save roughly 5% of cardiac energy — more than 3,300 pounds of food annually — and giraffes also evolved highly elastic blood vessels to manage extreme blood pressures.
04:03, 04.11.2025Science
Why giraffes evolved incredibly long legs
Giraffes are best known for their towering necks, but their legs are nearly as extraordinary. Adult giraffe legs measure about 6 feet, almost matching their 6-to-9-foot necks. Those long, slender limbs force giraffes into an awkward wide-legged stance to drink, which can slow their escape from predators.
The elaffe thought experiment
To investigate why giraffes have such long legs, researchers in Australia and South Africa designed a thought experiment: a fictional chimera named the elaffe, combining an elongated giraffe neck with the short, squat body and stubby legs of the common eland. Mathematical models of circulation in that hybrid body plan showed the arrangement would place dangerously high demands on the heart.
The study found that the elaffe would need to spend about 21% of its energy on circulation, compared with roughly 16% in a real giraffe and about 7% in humans. The researchers concluded that longer legs reduce the overall cardiac energy requirement by roughly 5%, an amount that they estimated translates to more than 3,300 pounds of extra food saved over a year. The results were published in the Journal of Experimental Biology.
Cardiovascular challenges and adaptations
Whether legs evolved before necks or vice versa remains uncertain, but both traits pose major cardiovascular challenges. Gravity helps push blood down to the lower limbs but increases the risk of blood pooling in the feet. Conversely, delivering blood to a brain positioned many feet above the heart requires extremely high arterial pressure — as much as three times typical human systolic pressure — and giraffes risk fainting when they rapidly raise their heads.
Evolutionary biologist David Barash, writing for Nautilus, described the giraffe's solution as a physiological hack: highly elastic vessel walls that act like biological compression socks to regulate blood flow and pressure.
In short, giraffes did not rely on long necks alone. Their long legs and specialized vascular system are integral parts of the evolutionary package that let them reach high foliage while keeping circulation in balance.
Sources: Journal of Experimental Biology; Nautilus (David Barash).