Giraffe necks help them regulate their body temperatures in hot African climates by increasing the surface area of their bodies, through which internal heat can escape. The idea that giraffes' necks help them regulate their body heat is actually not particularly new.
Brownlee put it forward as an idea in Researcher Graham Mitchell of the University of Wyoming has been thinking about it at least since , but now he and a team have put it to the test for the first time by looking at the body measurements of dozens of giraffes in Zimbabwe. What they found was that a giraffe's surface area is about what you'd expect for any other animal of the same mass.
However, the shape of their bodies could help them stay cool. In other words, they can turn their "flat" sides away from the direct sunlight, reducing the amount of heat on their skin. It's just one possibility, though, and gives another intriguing angle for ongoing study. Proceeds from every sale help fund our conservation work in Africa. We promise not to clutter your inbox. You'll receive our news updates once every 2 months. It's the best way to learn about our work and how you can get involved!
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Please check your email to confirm your subscription. You will not be subscribed until we receive your confirmation. All rights reserved unless otherwise stated. Hit enter to search or ESC to close. There is an ongoing anatomical debate about whether giraffes have only seven neck vertebrae or eight, the extra one being a modified part of the back. If you want to read up on the technical details of this hypothesis, see Nikos Solounias' paper on giraffe anatomy. Darwin, I was taught in my high school and college lectures, proposed that among an ancestral population of giraffes there were individuals which just happened to have slightly longer necks than their fellows.
This allowed them to reach higher branches, and as a consequence, these giraffes were more reproductively successful since they persisted on an untouched food source while giraffes of lesser stature perished due to competition.
Darwin did not explicitly consider the neck of the giraffe until much later, and when he did, it was in response to one of his most serious critics. In , the naturalist George Jackson Mivart published a book-length rebuttal to evolution by natural selection titled On the Genesis of Species.
Like many other late 19th century naturalists, Mivart accepted evolution but rejected natural selection, and one of the major points of his book was that natural selection could not account for the intermediate stages between an ancestral and descendant form. Likewise, the changes which must have occurred between the ancestral and modern giraffe must have extended beyond neck length alone. Various bits of anatomy and physiology would have had to have carried favourable variations in order for it to even be possible for giraffes to evolve long necks, and these changes — which would have increased the mass of the giraffe — would have required that it take in even more food under stressed, drought conditions.
Mivart had set up a straw man argument, but Darwin took this criticism seriously. Given the competition which would have occurred among herbivores during times of drought, Darwin surmised, it is not surprising that giraffes can reach a level of vegetation that others cannot — competition would drive forms apart rather than keep multiple forms in close competition by adapting them in the same way. Wallace considered this same point over a decade earlier. Giraffes, like any other species, expressed variation, and the ability of individuals to reach food inaccessible to others would have led to the success of the taller forms.
And, as far as drought conditions were concerned, Darwin countered that living giraffes were abundant in Africa. If the large, modern animals could survive temporarily stressed conditions, then why not intermediate forms which have since been replaced? What Darwin did not do was present a detailed, historical explanation for the form of the giraffe. Indeed, Darwin was typically careful in handling the history of life, and even when he was privately enthusiastic about fossil forms which exhibited transitional features — such as the feathered dinosaur Archaeopteryx — in his public works he avoided laying out precise step-by-step scenarios which would have taken place in the distant past.
Darwin knew that palaeontologists had only just begun to probe the fossil record, and so outlining phylogenies or tracing evolutionary lines of descent was a risky manoeuvre since those findings would almost certainly have to be revised.
The exchange between Mivart and Darwin did nothing to resolve the question of how giraffes had evolved. Proposing plausible adaptive scenarios was easy, but actually testing them has been another matter altogether.
The standard hypothesis, which is an extension of the argument Darwin outlined in , is that competition for food drove the evolution of elongated necks. Through competition for nutrition, natural selection would have resulted in the evolution of a giraffe able to reach otherwise unexploited resources above the heads of other herbivores. The idea that giraffes gain such a benefit was supported by one of the few experimental studies to look at this question.
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