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
Update, Jan 2023
Editors: While researching for their new book Titans of the Earth, Sea, and Air (above right), authors Dr Jonathan Sarfati and Joel Tay studied more up-to-date papers about blood pressure and very tall animals. The section (from pp. 97–99) is reprinted below. This information of course was not available to the author of the article at the time, who was following then-current research. The words in blue bold in both the book and extract are explained in the book’s glossary.
Coping with extreme height: giraffes and sauropods
Some of their design features have unfortunately not fossilized. But they must have had them to survive, as can be inferred by comparison with the giraffe. Because it is so tall (6 m), a giraffe must have a way of pumping blood uphill to its brain. So its heart is about 60 cm long, with walls as much as 7 cm thick, and a mass of 11 kg. This is needed to deliver blood pressure twice as much as humans: about 220/180, to deliver blood to its brain at 110/70.10
For comparison, normal human blood pressure is 120/80, while 140/90 is high blood pressure (hypertension). Even worse is a pressure at 180/120 or more—this is a hypertensive crisis that often requires hospitalization to prevent an imminent hemorrhagic stroke.
Also, humans with hypertension often develop thickened hearts that become stiffer because of too much connective tissue (fibrosis). The stiffening means the heart can’t refill with as much blood after every beat, a disease called diastolic heart failure. This causes shortness of breath and fatigue. But giraffes have large hearts without fibrosis.11
A giraffe heart also has a different rhythm from hearts of ‘ordinary’ animals. It delays the pump of the ventricles longer so that they have a chance to fill with more blood. This is why giraffes have no problem running fast and pumping lots of blood, even with a larger heart.
But what would happen if the giraffe bent down to drink—wouldn’t that high pressure, no longer working against gravity, cause a hemorrhagic stroke? For a long time, the explanation involved shunting off blood into the rete mirabile or ‘marvellous net’—a network of smaller blood vessels. [Reference to this article] But recent work shows that the blood pressure drops only about 0.5% in this network, so it wouldn’t protect the brain.12
The likely answer is that when the head is down, the big veins in the neck store over a litre of blood. This is blood that doesn’t reach the heart. Thus, the heart cannot generate its usual high blood pressure, so the brain is not overwhelmed. As soon as the giraffe lifts its head, the blood rushes back to the heart, which can then generate the high pressure needed to pump blood to the raised brain. That way it doesn’t have a dizzy spell like humans sometimes experience when they get up too quickly.13 This is an ingenious automated mechanical pressure regulating system.
And there are also design features needed for their long legs—to avoid both blood pooling and hemorrhage from a cut because of such high pressure assisted by gravity on top. Humans with hypertension often have swelling (edema) in their ankles because the pressure forces some water out of blood vessels into tissues. Sometimes they wear elastic support stockings or pressure bandages to compress tissues to keep water out. Giraffes have natural pressure bandages comprising both tight skin and tight fascia, the connective tissue surrounding and stabilizing muscles. This causes the tissue pressure in the lower legs to be about five times higher than in the neck, which resists swelling.14 Massive bleeding is prevented by having very deep veins, and very narrow capillaries supplying blood near the surface.
Since a giraffe requires very high blood pressure, a fortiori (even more so), the even taller Brachiosaurus would need an even higher blood pressure with a neck several times longer than a giraffe’s. The same must be true for the Diplodocid dinosaur Barosaurus, if it lived as it is often pictured or displayed rearing up, with its neck reaching very high. The larger sauropod hearts must have been much bigger even than a giraffe’s, and able to pump blood with pressure two or three times as high. And given the giraffe’s feedback mechanism to regulate blood pressure to the brain, its pressure bandages in the legs, we can only wonder at the design features that God must have programmed into the sauropods.
Some proposals have not won wide acceptance. For example, did long-necked sauropods have multiple hearts in the neck? However, no known vertebrate animal has more than one heart, although cephalopods such as squid do.15 Or, the larger animals floated on the surface of the water and used their long necks to feed on underwater plants.16 But as above, sauropods have many features of land-walking creatures.
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.
- Holmes, B., How giraffes deal with sky-high blood pressure, Knowable Magazine, bbc.com, 4 Aug 2021. Return to text.
- Baccouche, B. and Natterson-Horowitz, B., Giraffe myocardial hypertrophy as an evolved adaptation and natural animal model of resistance to diastolic heart failure in humans, International Society For Evolution, Medicine, and Public Health Conference, 15 Aug 2019. Return to text.
- O’Brien. H. and Bourke, J. Focus: Vascular ‘safety net’ doesn’t protect the brains of giraffes from dangerous pressure changes, anatomytoyou.com, 20 Jan 2019; Physical and computational fluid dynamics models for the hemodynamics of the artiodactyl carotid rete, J. Theoretical Biology 386:121–131, 7 Dec 2015. Return to text.
- Aalkjær, C and Wang, T., The remarkable cardiovascular system of giraffes, Annual Review of Physiology 83:1–15, Feb 2021. Return to text.
- Aalkjær and Wang, Remarkable cardiovascular system of giraffes. Return to text.
- Choi, D.S.J. and Ellis, R., Multiple hearts in animals other than Barosaurus, Lancet 352(9129):744, 29 Aug 1998. Return to text.
- Seymour, R.S., Cardiovascular physiology of dinosaurs, Physiology 31:430–441, 2016. Return to text.