Before giraffes became the skyscrapers of the savanna, evolution nearly gave them a heart attack. Scientists now believe their long legs came before their famous necks. That course of evolution may have allowed their hearts to keep up with the hefty demands of growing taller.
A study in the Journal of Experimental Biology found that the giraffe’s heart works harder than almost any other mammal in the animal kingdom. It burns about 16% of their resting energy just to push blood to the brain, nearly twice the amount required for similar-sized species. Without their long legs raising the heart higher, that energy cost would rise to 21%, a strain that researchers say could make life unsustainable.
Roger Seymour, from the University of Adelaide, and Edward Snelling, from the University of Pretoria, created a computer model to test the theory. They imagined an “elaffe,” a mix of giraffe and eland, with short legs but the same long neck. The result showed extreme blood pressure, around 286 mmHg, compared to the giraffe’s typical 200. The model confirmed that leg length directly reduces the work required to pump blood upward.
Turns Out Giraffes Got Their Long Legs First—and It Probably Kept Them Alive
Fossil records show this adaptation began around 16 million years ago. Early giraffids already had long limbs with relatively short necks. Later species started to balance the two more evenly. The sequence implies that evolution raised the heart first, giving the circulatory system time to adjust before the neck began its climb skyward.
Evolution can only go so far, though. The lungs sit near the heart, and if blood pressure climbs too high, fluid can leak into the air sacs, causing suffocation. That boundary may explain why no land animal has ever developed a taller, upright body than the giraffe. Even giant dinosaurs likely kept their necks extended forward rather than vertical to avoid collapsing under the same pressure problem.
Those stilts of bone and muscle might look awkward, but they are precision-built for survival. Evolution found a balance that lets giraffes walk among treetops without their hearts giving out.
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