14 DAY TRIAL // Although they look stunningly beautiful, with their long necks stretching over the top of trees, giraffes also posed a difficult challenge for evolution, in terms of making them capable of surviving. What is beautiful about them – the long and thin neck – also comes with a disadvantage, and namely the fact that the head is very far away from the heart. In humans, the distance is between 20 and 40 centimeters, between the brain and the “blood pump.” In the savanna animals, the distance is longer than 1 meter, maybe even two, so getting blood to the brain is difficult, the BBC News reports.
Evolution had three options when it “constructed” the giraffe. It could have made its heart extremely large, such as the one dinosaurs had. A larger heart means more muscles, and therefore more power transmitted to the bloodstream, which could thus reach the brain. The second option was to create an average-sized, but extremely powerful heart, capable, in short bursts, of sending the blood to its destination. The third option was do nothing altogether, and leave the animals to die off.
As history shows us, natural selection decided on the second, providing the giraffe with a “supercharged” heart. Details of the discovery are currently published in the latest issue of the respected scientific journal Comparative Biochemistry and Physiology, Part A. Researchers say that the organ, which is like that of no other animals, is capable of propelling blood to a brain located more than 2 meters away with relative ease. In charge of the new research were experts from the Center of Wildlife Studies (CWS), in Onderstepoort, South Africa, and the University of Wyoming, in the US.
“There are not many animals that have evolved to have a very long neck. Giraffes have this very funny long neck, and two questions immediately arise, one is why and the other is how. Giraffes have this huge problem of having a head that is 2 meters away from the heart. So in a really big animal, how does it get blood up there?” asks CWS giraffe expert, professor Graham Mitchell. He conducted the research together with UW colleague, professor John Skinner.
The key is the fact that the giraffes have an abnormally high blood pressure, to which they are perfectly adapted. “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. 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. You have a small but a very powerful heart delivering the blood pressure,” Mitchell adds.
“Blood pressure depends on the capacity of the cardiovascular system as well as the efficiency of the pump. Giraffes have got a way of adjusting the capacity of the cardiovascular system and are able to shrink and expand their blood vessels to change the volume of the cardiovascular system very efficiently,” the expert concludes.