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Do Giraffes Have Two Hearts?

Updated: Jan 5, 2021

giraffe with two brains high blood pressure
It was thought that the giraffe had two hearts that enabled blood to reach its heady heights

The distinctive shape of the tallest mammal has long now prompted two main questions.

Why is the neck so long?

How is it possible for blood to reach the brain?

To answer the first question, could be considered fairly self-evident when you see giraffes grazing from the very tops of thorny acacia trees. Interestingly, the manner in which giraffes feed reduces friction between the males and females. Cows bend down to reach lower branches of trees and shrubs, whilst the bulls get their diet by reaching up to the treetops.

giraffes eating from treetops
Giraffe cows bend down to reach lower branches of trees and shrubs, whilst the bulls get their diet by reaching up to the treetops.

Other reasons could be to thermo-regulate their body temperature with its large surface area plus also the visual benefits from having a height advantage. To answer the second question, How is it possible?, Giraffe expert Prof Graham Mitchell from the Centre of Wildlife Studies, South Africa undertook a study along with Professor John Skinner from the Centre for Veterinary Wildlife Studies, also of South Africa.

giraffe necks 2m long
Studies have proven that their blood pressure is twice that of other mammals.

"Giraffes have this huge problem of having a head that is 2m away from the heart", Prof Mitchell said. "So in a really big animal, how does it get blood up there?" It is understood that most mammals have a comparably low blood pressure because their blood has to move only a relatively short distance from the heart to head; it is significantly longer for the giraffe! In fact, earlier studies have already proven that their blood pressure is twice that of other mammals.

That creates two challenges:

A giraffe's heart must cope with the pressure exerted on it by the amount of blood in such a long neck for the head to receive a blood supply, the heart needs to beat with enough force to overcome the significant downward gravitational pressure

The researchers study went on to understand the true mechanics of the giraffe’s heart and its cardiovascular system... "For a long time it was thought that the origin of the high blood pressure was a really big heart and that was based on a single measurement based in the 1950s," said Prof Mitchell.

giraffes neck too short to reach the ground
A giraffe's neck is too short to reach the ground

"Our concern was partly to explain the origin of high blood pressure and what physiological mechanisms operate to push the blood pressure to the level in the giraffe," he said. "We established that the heart is actually quite small. It's smaller than you'd expect in similar-sized animals, but the walls are incredibly thick," Prof Mitchell said. "You have a small but a very powerful heart delivering the blood pressure." Its heart has evolved thicker muscle walls and a smaller radius, endowing it huge power. Additionally, to avoid rupture, as the giraffe matures and pressure increases as its neck lengthens, the blood vessel walls thicken.

wildlife giraffe long neck acacia tree eating
A giraffe's head is 2m away from its heart

Data collected from the body dimensions of deceased giraffes, the researchers hope to gain insights into this remarkable animal, including revealing details of its breathing and range of vision. Prof Mitchell said, "To measure blood pressure in a free living giraffe doing its thing, that would be really interesting for people who study high blood pressure in humans, or people just like me who wonder how giraffes get it right."


Giraffe Stats:

  • Distribution: across 15 sub-Saharan African countries in open woodland and grassland

  • Height: 4.7-5.3m (m), 3.9-5m (f)

  • Weight: 800-1930(m) 550-1180(f) (kg)

  • Tongue: up to 45cm long

  • Top speed: 35 mph short distances

  • Cruise: 10 mph longer distances

  • A giraffe's neck is too short to reach the ground

  • Lifespan: 25 years in the wild

  • There are 4 distinct species of giraffe: Northern, Reticulated, Masai and Southern

  • These 4 species separated millions of years ago

  • Nine subspecies of giraffe are recognised, all very similar but distinguished by coat pattern and geographical distribution

  • Current estimation: 97,500 (140,000 in 1999; 80,000 in 2014)


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