Walking Tall … by Design
The giraffe is an animal that certainly stands ‘head and shoulders’ above every other animal. An adult male can reach a height of 3 metres (10 feet) at the shoulder, with a neck that can extend for a further 2.5 metres (8 feet). Its front legs are about 10% longer than the hind legs.
There are few more iconic images of Africa than a group of these magnificent creatures silhouetted against the warm oranges of the setting sun. Their uniquely long necks and stilt-like legs give the appearance of slowness to their graceful, almost casual way of moving. Yet, an adult giraffe can give most other creatures ‘a run for their money’, with a top speed of around 55 km/h (34 mph).1
The giraffe (Giraffa camelopardalis) is an even-toed ungulate (hoofed animal). It is also the world’s largest ruminant (animals that partly digest their food and then regurgitate it to chew as ‘cud’).2 The giraffe is placed in the family Giraffidae, a group that contains only two animals— the other being the Okapi. This is a curious animal in its own right, with a giraffe-like head, zebra-striped legs and hindquarters, and a body shape much like that of a large gazelle.
Far more than just a beautiful and impressive animal to look at, the giraffe has a whole range of interesting design features. These mostly either involve supporting its amazing neck or are in some way related to it. Long and powerful, this 225 kilogram (500 pound) structure enables the giraffe to reach foliage that other species can only dream of.
Yet, despite its impressive size, the giraffe’s neck still contains just seven cervical vertebrae (neck bones). This is the same as most other mammals—but the giraffe’s vertebrae are of course longer (up to 25 cm = 10 in) and they are bound together with ball-and-socket joints.3 This is the same kind of joint that links our arm to our shoulder, giving a 360-degree range of motion. So the bony structure of the giraffe’s neck demonstrates an excellent balance of weight, flexibility and durability. Indeed, so durable is a giraffe’s neck, that adult males will enthusiastically club one another with them in order to win mates.
To further assist in supporting the neck, the vertebrae over the shoulders have long vertical extensions, which allow for a very large ligament (the nuchal ligament, which runs from the back of the skull all the way down to the base of the tail, but it is at its thickest just over the shoulders). This ligament helps counteract the weight of the giraffe’s head and neck, acting like a giant rubber band, pulling the neck up. This means very little muscular energy is required to hold the head up.
Having one’s head perched approximately 5.5 metres (18 ft) in the air may provide an excellent view and premium browsing options, but it does pose the problem of how to get the blood all the way up there. The higher you need to push a liquid up a pipe against gravity, the more powerful a pump you need. Thankfully, the Creator knew about this and furnished the giraffe with a suitably large heart (up to 60 cm (2 ft) long in an adult male), which generates a blood pressure about twice that of a human or other large mammal. The artery walls have extra elasticity to ensure that they can handle this high pressure close to the heart. Furthermore, to prevent the blood from rushing too quickly back down the neck again, the jugular veins in the neck partially contract to restrict return flow.4
Now this is all very well for when the giraffe is walking around with its head up, but what about when it wants to take a drink? When it lowers its head, all that high pressure blood would likely rush downhill (further assisted by gravity) and blow out the delicate blood vessels in the brain and eyes—if it weren’t for a series of clever mechanisms working in concert with one another. When the head is lowered, special shunts in the arteries supplying the head restrict blood flow to the brain, diverting it into a web of small blood vessels (the rete mirabile or ‘marvellous net’). This network of vessels near the brain gently expands to accommodate the increased local blood pressure. Valves in the jugular veins also prevent returning blood from flowing backward while the head is lowered.
All of this is controlled by a complex series of mechanisms that constantly monitor the pressure in the blood vessels and make whatever adjustments are needed to ensure that the proper pressure is maintained in all situations. This means that even if the giraffe lifts its head up quickly mid-drink (perhaps in response to a nearby lion), proper blood supply is maintained to the brain, so that the giraffe doesn’t faint (probably much to the lion’s disappointment—a giraffe can kill a lion with its powerful kick).
Of course, this high blood pressure, combined with the effect of gravity on such a tall body, would also be a problem for the giraffe’s legs. The animal would bleed profusely from any cut, and there is a very real danger of blood pooling in the lower extremities. To combat this, the skin on the giraffe’s legs is extremely tough, and tightly fitted by way of a firm inner fascia5 to prevent blood pooling. (This has been studied by NASA scientists developing the special ‘gravity-suits’ worn by astronauts to help maintain correct circulation while in space.6) To prevent excess bleeding, the blood vessels in the giraffe’s legs run deep (away from the skin’s surface), and those capillaries that do reach the surface are very narrow, with blood cells only 1/3 the size of ours. Additionally, these smaller blood cells allow for faster absorption of oxygen, ensuring a good supply to the extremities of such a large animal.
Many have asked how the giraffe got all these interesting features. Some suggest that you can start with a non-giraffe and, through successive small changes, end up with a giraffe. However, the fossil evidence of giraffes in the past shows them to be much the same as the ones we see in Africa today. Fossil evidence of transitional forms, or ‘not-quite-giraffes’, is “completely lacking”.7 The selective advantage of a long neck for reaching higher leaves in a drought is often discussed, but this does not account for the survival of baby giraffes (who are unable to reach this food supply). And female giraffes would have a selective disadvantage because they are shorter. In addition, giraffes spend a good portion of their time, legs splayed, browsing grass or low-lying shrubs.8
In any case, the idea that the neck became elongated stepwise over successive generations under environmental/selection pressures is now shown to be a great deal more complex than previously thought, with a whole assortment of structures and systems that need to be in place to accommodate the long neck. Many of these features involve and affect parts of the body seemingly unrelated to the neck, but nonetheless connected through the necessities of function or support. It illustrates the point that an organism is a finely balanced collection of interconnected (and often interdependent), systems. And the only One who can achieve such a delicate balancing act is the creative Genius who designed it in the first place.
The giraffe’s scientific name (Giraffa camelopardalis), is similar to its older English name of camelopard. It refers to its irregular patches of colour on a light background, which bear a token resemblance to a leopard’s spots, and its face, which is similar to that of a camel.
With their long legs, giraffes walk by moving both legs on one side of their body forward at the same time—known as ‘pacing’ (other quadrupeds usually walk by moving diagonally opposite limbs forward at the same time). This allows a longer stride, thus fewer steps and less energy used.
The irregular brown markings that cover most of its body are unique to each giraffe, like fingerprints in humans. They were often thought to be for camouflage, but giraffes show no interest in hiding—fairly pointless for such a towering beast anyway. Instead, the markings are used as thermal windows to regulate temperature. Each one has a large blood vessel around its border; by directing blood flow to or away from the smaller vessels branching off to the centre, the giraffe can radiate heat away or retain it as appropriate.
The collective name for a group of giraffes (as in ‘pride of lions’ or ‘gaggle of geese’) is a ‘journey of giraffes’.9
References and notes
- Estimates within the literature vary from 50–60 km/h (30–37 mph). Return to text.
- Giraffe—the facts: Taxonomy, evolution and scientific classification, giraffeconservation.org, accessed July 2011. Return to text.
- Conger, C., If a giraffe’s neck has only seven vertebrae, how is it so flexible?, animals.howstuffworks.com, accessed July 2011. Return to text.
- Pedley, T., Giraffes’ Necks & Fluid Mechanics, abc.net.au, (from transcript of broadcast 25 October 2003). Return to text.
- Fascia is a connective tissue that, in this instance, lies directly under the skin and serves as a means to flexibly bond the skin to the muscles underneath it. Return to text.
- Hofland, L., Giraffes … animals that stand out in a crowd, Creation 18(4):10–13, 1996; creation.com/giraffe. Return to text.
- Lönnig, W.-E., The Evolution of the Long-Necked Giraffe (Giraffa camelopardalis L.) what Do We Really Know? (Part 1), weloennig.de, accessed March 2006. Return to text.
- Dagg, A and Foster J., The Giraffe: Its Biology, Behavior, and Ecology, Robert E. Krieger Publishing Company. Malabar, Florida, 1982. Return to text.
- African wildlife: Giraffe Facts, southafrican-wildlife.blogspot.com, accessed July 2011. Return to text.