The giraffe has some highly unusual and specific adaptations, among which at least one that demonstrates how evolution must work with the "materials at hand" rather than being able to come up with more elegant engineering solutions. Richard Dawkins explains one such compromise in the following video.
https://www.youtube.com/watch?v=cO1a1Ek-HD0
A word about Dr. Dawkins. He has had some controversial things to say on subject matter that technically lies outside of science. Feel free to agree or disagree with his opinions on non-scientific topics. But when it comes to evolutionary biology, Dawkins is in fact a leading light (his brilliant book "The Selfish Gene" is seminal), and he is not expressing opinion but explaining biological facts.
One fact about giraffes--again, something that points toward common descent--that is surprising is that they have the same number of vertebrae in their necks as humans and most other mammals. You can see from the photo of the model giraffe that one reason for that is that the bones are elongated. Human cervical (roughly, "neck") vertebrae are short, compact, and closely nested. You can see that this is not the case with giraffe cervical vertebrae. Again, this is typical of what evolutionary processes must do--make do with materials at hand. It might have been an advantage to have more, smaller bones in terms of flexibility (and in fact, in snakes this adaptation DID occur), but just because an organism might benefit from some feature does not mean it will get it. Novel features are largely determined, initially, by chance,and those differences that confer a survival and reproductive advantage spread throughout the species population. Over geological time (thousands of years), advantageous features accumulate, bringing about usually gradual (rarely, less gradual) change.
Other adaptations that enable the giraffe's unique body plan include those related to the circulatory system. Consider the problem--getting an adequate blood supply all the way up that long neck into the brain, and, if the giraffe, say, has to bend down to get a drink, the pressure can't, oh...make its little noggin explode? So the giraffe has evolved some unusual hydraulic equipment, which top-notch science writer Natalie Angier explains in the October 7 2014 New York Times:
Also of interest is the giraffe’s exceptional cardiovascular system. A large giraffe can stand 20 feet tall — the height of a second-story window — with its neck accounting for roughly a third its span and its long legs the same. The multitiered challenge, then, is how to both pump blood very high and retrieve it from far below while avoiding burst capillaries in the brain or blood pooling around the hooves.
As part of the Danish Cardiovascular Giraffe Research Program, scores of scientists have traveled to South Africa to study giraffe physiology. They have measured blood pressure at different sites and found readings that range from high to ridiculous — up to five times human blood pressure — yet with none of the organ damage commonly seen in hypertensive patients.
Instead, the giraffe has extremely thick blood vessel walls to prevent blood from leaking into surrounding tissue, while rugged, inflexible collagen fibers in its neck and legs help keep the blood traffic moving, rather as the tight antigravity suits worn by astronauts and fighter pilots will maintain blood flow under the most extreme gravitational shifts. A complex mesh of capillaries and valves store and release blood in the neck, allowing the giraffe to bend over for a drink of water and then raise its head again quickly without fainting; when the giraffe is standing still, sphincters at the top of the legs limit circulation to the lower extremities, to minimize the risk of fluid buildup around the hooves.
Researchers were also surprised to find that contrary to old textbook wisdom, giraffes do not have unusually large hearts for animals their size. “It’s half a percent of body mass, and that’s the same as we see in a cow, dog or mouse,” said Christian Aalkjaer of the department of biomedicine at Aarhus University in Denmark.
Moreover, Dr. Aalkjaer and his colleagues have determined that the giraffe’s cardiac output — the amount of blood pumped into circulation each minute — is modest, proportionally lower than it is in humans. That finding could help explain why giraffes rarely run for very long: Their hearts can’t deliver oxygen to their muscles fast enough to power extended aerobic exertion.
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