Figure 1. Giraffe in a

Figure one. Giraffe in a "classic" feeding position, extending its neck, head, and tongue to reach the leaves of an Acacia tree. (Tsavo National Park, Kenya; drawing by C. Holdrege)

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Lamarck and Darwin

Once scientists began thinking about animals in terms of evolution, the giraffe became a welcome — and seemingly straightforward — example. It is as if the giraffe's long neck was begging to exist explained by evolutionary theorists.

One of the kickoff evolutionary thinkers, Jean-Baptist Lamarck, offered a brusk description of how the giraffe evolved in his major work, Philosophie Zoologique, which was published in 1809:

It is interesting to observe the result of habit in the peculiar shape and size of the giraffe: this animal, the tallest of the mammals, is known to live in the interior of Africa in places where the soil is most always arid and barren, and then that it is obliged to browse on the leaves of trees and to brand constant efforts to reach them. From this habit long maintained in all its race, it has resulted that the animal'due south forelegs have become longer than its hind-legs, and that its neck is lengthened to such a degree that the giraffe, without standing up on its hind-legs, attains a height of vi meters. (Quoted in Gould 2002, p. 188)

In Lamarck'due south view, we must imagine a situation in the by where the all-time food for browsing mammals was college upward in copse, the lower vegetation having been eaten by other animals. The ancestors of the giraffe — which nosotros should imagine similar antelopes or deer — needed to adapt their behavior to this changing environment. As Lamarck wrote, "variations in the environment induce changes in the needs, habits and modes of life of living beings ... these changes give ascension to modifications or developments in their organs and the shape of their parts" (p. 179). So Lamarck imagined that over generations the habit of continually reaching for the higher scan produced in the giraffe'southward ancestors a lengthening of the legs and neck.

A little over lx years later, Charles Darwin commented on giraffe evolution in the sixth edition (1872) of his seminal book, Origin of Species:

The giraffe, past its lofty stature, much elongated neck, forelegs, head and tongue, has its whole frame beautifully adapted for browsing on the college branches of trees. It tin thus obtain food beyond the reach of the other Ungulata or hoofed animals inhabiting the same land; and this must be a great advantage to it during dearths.... Then under nature with the nascent giraffe the individuals which were the highest browsers, and were able during famine to achieve even an inch or two in a higher place the others, volition often accept been preserved; for they volition have roamed over the whole country in search of food.... Those individuals which had some one part or several parts of their bodies rather more elongated than usual, would generally have survived. These volition take intercrossed and left offspring, either inheriting the same bodily peculiarities, or with a tendency to vary once again in the same manner; whilst the individuals, less favoured in the aforementioned respects will accept been the most liable to perish.... By this procedure long-continued, which exactly corresponds with what I have called unconscious selection past human, combined no dubiousness in a nearly important mode with the inherited effects of the increased use of parts, it seems to me almost sure that an ordinary hoofed quadruped might be converted into a giraffe. (Darwin 1872, pp. 177ff.)

In many respects this is a classic formulation of how Darwin viewed evolution: every species consists of individuals that bear witness considerable variations. Under certain environmental conditions particular variations will be almost advantageous. Natural selection weeds out the unadapted and the best-adapted survive. These variations become dominant in the species and then it evolves. In the case of giraffes, times of drought and arid conditions give an advantage to those animals that can out-compete others past reaching the college, untouched leaves. They form the ancestral stock of the animals that evolve into giraffes.

Interestingly, Darwin believed in the "inherited effects of the increased use of parts" — a very "Larmarckian" view. Lamarck argued for the inheritance of acquired characteristics. Darwin felt that this was primal to explain giraffe evolution; otherwise in that location is no guarantee that longer features in one generation volition have an outcome on subsequent ones. But this view of the inheritance of caused characteristics is rejected by mainstream Darwinists today.

The Long Neck equally a Feeding Strategy

The thought that the giraffe got its long neck due to food shortages in the lower reaches of trees seems near self-evident. The giraffe is taller than all other mammals, can feed where nearly no others can, and therefore has a singled-out advantage. Information technology seems compelling to say that the long neck and legs adult in relation to this advantage. Why else would the giraffe be and so tall? You find this view presented in children's books, in web descriptions of the giraffe, and in textbooks.

But just because this caption is widespread does not hateful information technology is true. In fact, this "cocky-evident" caption retains its ability to convince only as long as we exercise not become too involved in the actual biological and ecological details. Diverse scientists take noticed that this elegant film of giraffe evolution dissolves under closer scrutiny. Hither are a few examples of my and their objections:

1) Since the taller, longer-necked, evolving giraffe ancestors were also larger and heavier, they would need more food than the animals they're competing with. Wouldn't this counterbalance their reward in times of dearth? Would they really have any advantage over smaller members of the same and other species? Moreover, information technology is absurd to assume that only the leaves on high branches were available to the giraffe during a drought. Had this been the example, and so the multitude of browsing and grazing antelope species in Africa would all have gone extinct (or never evolved in the first identify). So, even without growing taller, the giraffe ancestor could have competed on even terms for those lower leaves.

ii) Male giraffes today are up to 1 meter taller than female giraffes; newborn and young giraffes are much smaller. The moment this sexual dimorphism manifested in the development of the giraffe, it would have been the males that could have reached the college branches. The females and immature animals would accept died and the species would have gone extinct (Pincher 1949).

Figure 2. Giraffe feeding at about shoulder height — the most prevalent height at which giraffes feed. (South of Moremi Game Reserve, Botswana; drawing by C. Holdrege.)

Figure ii. Giraffe feeding at about shoulder elevation — the well-nigh prevalent pinnacle at which giraffes feed. (South of Moremi Game Reserve, Botswana; drawing by C. Holdrege.)

three) If giraffes evolved past eating high leafage during times of drought and maximal contest for nutrient, one would expect that giraffes today would likewise feed from the high foliage during these times in order to avert contest. Males commonly feed at greater heights than females and the results of i study show a surprising spread (Ginnett and Demment 1997). Male giraffes fed nearly half of the time at heights of almost five meters, that is, in the "classical" long-necked giraffe posture. In stark dissimilarity, females fed around seventy percentage of the fourth dimension at belly height or below, which the theory demands they should non be doing. These researchers did not written report on the seasons in which they made these observations, so their results are of little help in discerning whether, for instance, males feed at greater heights mainly during droughts.

A diversity of other studies prove that giraffe feeding habits vary according to place and time (reviewed in Simmons and Scheepers 1996). Giraffes move seasonally, and in the dry season in East Africa they tend to seek out lower valley bottoms and riverine woodlands. There they ordinarily feed from bushes at or below shoulder height (nearly two and i half meters in females and three meters in males). L percentage of the time they fed at a height of two meters or less, which overlaps with the feeding zone of larger herbivores such as the gerenuk and the kudu (Leuthold and Leuthold 1972; Pellew 1984). During the rainy season, when there is abundant browse at all levels, giraffes are more than likely to feed from the higher branches, browsing fresh, protein-rich leaves. Other studies besides evidence that giraffes do most of their feeding at about shoulder peak, with their necks positioned virtually horizontally (Young and Isbell 1991; Woolnough and du Toit 2001; meet Effigy 2). So it looks equally though giraffes are not using their long necks the way the theory demands. And they use them even less to accomplish heights in the dry flavor, when the theory demands they should need them most!

Figure 3. A goat does not require a long neck to feed on twigs and leaves of an oak tree. (Drawing by C. Holdrege after a photo in Butzer 2000.)

Figure 3. A caprine animal does not require a long neck to feed on twigs and leaves of an oak tree. (Cartoon by C. Holdrege after a photo in Butzer 2000.)

4) At that place are other ways to reach the high leaf of trees. Goats, for instance, are known to climb into trees and swallow leaf (see Figure 3). Why didn't tree-climbing leafage-eaters (folivores) develop in the savannah? They would have had the advantage of feeding at all levels easily and been in that respect more adaptable than the highly specialized giraffe. The long-necked gerenuk, an antelope, ofttimes stands on its hind limbs and browses, reaching heights of two meters and more than. The much larger and heavier elephant even stands sometimes on its dorsum legs and extends its trunk to reach loftier limbs — but no one thinks that the elephant developed its trunk equally a result of pick pressures to attain higher nutrient.

In sum, there is nothing in this theory that shows a compelling link between leg and neck lengthening and feeding on high limbs. Just considering giraffes have long necks and long legs and can reach food high in the copse does non hateful that a need to achieve high browse was a causative cistron in the evolution of those characteristics.

 Clearly, both Darwin's and Lamarck's conceptions of giraffe development were highly speculative. The thought that giraffes developed longer legs and necks to attain higher food seems plausible, even compelling, as long as we do not (1) call up the idea through in all its implications and (two) take into business relationship essential observations of giraffe behavior and ecology. In the terminate, the idea is neither logically compelling nor based on fact.

Alternative Explanatory Attempts

Pincher (1949), after critiquing Darwin's explanation, suggests that the "nigh extraordinary feature of the giraffe is not the length of the neck just the length of the forelegs." By developing long legs, the giraffe has acquired a huge stride so that information technology can move relatively fast for its size. This has left the giraffe with merely one predator — the panthera leo. Pincher therefore explains the "excessive length of its fore-legs every bit the effect of natural choice interim continually through the hunter-hunted relationship, equally in the instance of hoofed mammals generally." The cervix, in turn, followed the lengthening legs then that the giraffe could still reach the basis and drinkable.

It is strange that Pincher is able to critique Darwin'southward view and so clearly and however doesn't recognize that he is proposing the same type of inadequate explanation. The giraffe ancestor could just as well have developed greater bulk or more than running muscles, both of which would have aided in avoiding predators. The fact is that despite its size and long footstep, the giraffe is however preyed upon past lions. And as i report of one hundred giraffes killed by lions in Southward Africa showed, almost twice as many bulls were killed every bit cows (Pienaar 1969; cited in Simmons and Scheepers 1996). The longer stride of bulls plain doesn't assistance them avoid lions better than the shorter legged females. Who knows whether their long stride may in some way brand them more vulnerable? Another speculative idea into the wastebasket.

Brownlee (1963) speculates that the lengthening of the limbs and neck in the giraffe give the giraffe a relatively big surface area, which should allow it to misemploy estrus. This would exist of advantage in the hot tropical climate, then that the tendency toward lengthening would take been encouraged past natural selection, since the largest animals would have been best able to survive heat waves.

Equally in the other suggested "explanations," the cardinal question is, Is Brownlee's idea rooted in reality? Because of its long legs and neck, the giraffe appears to accept a big surface surface area. Just expanse alone is not important; it is the relation of the heat producing volume to surface expanse that is crucial. A small creature has a pocket-sized book in relation to a very large surface surface area, while a large beast has a very big volume in relation to its relatively small surface area.* At present the giraffe is a very large animal with a barrel-shaped torso. Although its neck is long, it is also voluminous; only the lower parts of the legs, which carry relatively few claret vessels, would human action to overstate the surface-to-volume ratio essentially. Krumbiegel (1971) estimates that the ratio of volume to surface in the giraffe is 11:one, compared, say, to a smaller, long-necked antelope, the gerenuk, which has a ratio of iv.7:i (like to the human). In other words, despite appearances, the giraffe still has a very big book in relation to its surface area and its unique form provides no grounds to retrieve that it evolved in relation to dissipating oestrus.

More than recently, Simmons and Scheepers (1996) proposed that sexual selection has caused the lengthening and enlarging of the neck in males. These scientists place their ideas in relation to known facts and bespeak out shortcomings in relation to larger contexts — a happy contrast to the other hypotheses we've discussed. They describe how male giraffes fight by clubbing opponents with their big, massive heads; the neck plays the role of a muscular handle. The largest (longest-necked) males are dominant among other male giraffes and mate more ofttimes. Since long-necked males mate more oft, selection works in favor of long necks. This would also assist explicate why males have not merely admittedly longer, just proportionately heavier heads than females. This hypothesis seems consistent with the deviation between male and female giraffes. At to the lowest degree information technology gives a pic of how the longer neck of males tin exist maintained in development. But information technology doesn't tell united states anything virtually the origin of neck lengthening in giraffes per se — the cervix has to reach a length of one or two meters to be used every bit a weapon for clubbing. How did it get that long in the first place? Moreover, the female giraffe is left out of the explanation, and Simmons and Scheepers tin can only speculate that female cervix lengthening somehow followed that of males. In the end, the authors admit that neck lengthening could have had other causes and that head clubbing is a consequence of a long neck and not a cause.

Does the Giraffe Really Accept a Long Neck?

All the above explanations of the evolution of the giraffe'southward long legs and long neck are unsatisfying. Each of the authors sees problems in other explanations, only remains within the same explanatory framework when putting forward his ain hypothesis. No one sees the necessity for stepping outside the framework and looking at the difficulties of the overall approach. The scientists abstract individual features (long neck, long legs, large surface expanse) and consider them in isolation from the residuum of the organism. The individual characteristic is and so placed into relation to 1 purported causal factor in the environment (drought, estrus, predator avoidance, male competition). The link of individual feature to environmental factor is supposed to explain the development of that feature.

But this is a highly problematic procedure. The giraffe's neck carries out a multifariousness of functions — it allows feeding from high branches, serves as a weapon in males, brings the caput to elevated heights that requite the giraffe a large field of view, is used as a pendulum while galloping, and and so on. Virtually all structures and organs in the animate being body are multifunctional and interact dynamically with other multifunctional structures and organs. When scientists pick out a single function and focus solely on it to explain a multifunctional organ, their explanation can only exist inadequate. This is comparable to assertive you tin pigment a richly-nuanced, colorful rendition of a mural with 1 color. It just does non work.

Figure 4.

Figure 4. "Short-necked" giraffes grazing. Giraffes can merely reach the footing with their mouths to potable or graze past splaying their front legs (left) or splaying and bending their legs (correct). (Drawing by C. Holdrege after a photo in Dagg and Foster 1982.)

I sometimes wonder why no one has maintained that the giraffe has, in reality, a curt neck. If you lot find a giraffe drinking or, every bit they occasionally do, grazing shut to the ground, and so you know what I mean (see Figure 4). Giraffes do not potable often, but when they practice, they have to either splay their forelegs to the side or curve their forelegs strongly at the wrist joint. Both procedures take time and are bad-mannered for the giraffe. Merely just in this way tin can it get the tip of its rima oris down to the surface of the water. So, looked at from the perspective of drinking, the giraffe has a very short neck. Antelopes and zebras accomplish the footing without angle their legs, and the long-legged elephant has its torso to recoup for its curt neck. Merely the giraffe (and its rain forest relative, the Okapi) take necks that are and then short relative to their legs and chest that they must splay or bend their legs.

So why hasn't the giraffe become famous for its evidently brusque cervix? Why don't we have evolutionary hypotheses explaining how the giraffe got its short cervix? It is because the giraffe'southward neck, in other respects or from other perspectives, is long. No other mammal has such a long neck in absolute terms or in relation to the length of its body. Nosotros all have seen (in life or in pictures) and been amazed by the standing giraffe, its long neck sailing skyward, in comparison to which the ungainly, brusque-necked drinking giraffe appears every bit exceptional, about unfortunate behavior.

Whether the cervix is long or short depends on our perspective and on the behavioral or anatomical context we are focusing on. We but understand the giraffe when we view information technology from diverse perspectives and allow the giraffe testify dissimilar aspects of its existence. The moment we focus solely on the "long cervix" — and on it solely in terms of a food-gathering or some other strategy — we've lost the reality of the giraffe.

Reality is richer than such explanations. The caption may exist coherent and logical, but what information technology explains is non the thing itself just a specter of it — the isolated aspect that has been abstracted from the whole organism. In reality, the organism every bit a whole evolves; all its parts are multifunctional, facilitating its interactions with its circuitous, changing environment. If we don't consider all partial aspects within this larger context, we can merely take inadequate explanations void of life.

In sum: the whole projection of explaining the evolution of an beast by abstracting from the whole leads to unsatisfying, speculative ideas on the one mitt, and to conceptual dissolution of the unity of the organism on the other. A more acceptable agreement requires that nosotros first investigate the organism as a whole and how its members interrelate and interact within the context of the whole organism and its surroundings. This holistic understanding tin can then class the starting betoken for thinking about the evolution of the creature. The evolutionary biologist Dobzhansky's famous statement that "nothing in biology tin be understood except in low-cal of evolution" is a grand merits, which I believe is, in the end, true. But we have a lot of work to practise before we get at that place, and we should not exist satisfied with short-cut evolutionary "explanations." Another issue of the usual fashion of explaining is that the organism itself is atomized into individual characteristics, each having its own explanation. Each function takes on a quasi-reality of its ain, while the whole organism — which brings forth and gives coherence to the parts — degenerates into a kind of epiphenomenon, a mere composite of the surviving parts that "really" count.

If evolutionary thought is to have a solid foundation, nosotros must constitute this firm grounding in holistic understanding. As information technology is, stories of the evolution of traits seem compel-ling until you look for their context and foundation in the world and discover a pool of quicksand. As Simmons and Scheepers remark about Darwin's idea of giraffe evolution, "it may exist no more than a tall story."

* Assuming for the sake of explanation a spherical body, the two-dimensional surface grows as a office of the foursquare of the radius, while the volume — existence 3-dimensional — grows as a function of the cube of the radius. A small sphere with a radius of 2.5 cm (1 inch) has a volume-to-surface ratio of 0.viii:i. A much larger sphere with a radius of l cm (about 20 inches) has a volume-to-surface ration of 16.vii:1.

For more than of Craig's work on the giraffe, see the article "The Giraffe in Its Globe" and the monograph "The Giraffe's Long Neck." Other articles on whole organism biology can be viewed here, or y'all can find Craig'due south latest book on the topic, Seeing the Animal Whole—And Why It Matters, at our bookstore.

References

Brownlee, A. (1963). "Evolution of the Giraffe," Nature vol. 200, p. 1022.

Butzer, Karl (2000). "The Human being Role in Ecology History," Nature vol. 287, pp. 2427-2428.

Dagg, Ann Innis, and J. Bristol Foster (1982). The Giraffe: Its Biology, Behavior and Ecology. Malabar FL: Krieger Publishing Company.

Darwin, Charles (1872). Origin of Species. Sixth Edition.

Ginnett, Tim, and Montague Demment (1997). "Sex Differences in Giraffe Foraging Behavior at Two Spatial Scales," Oecologia vol. 110, pp. 291-300.

Gould, Stephan Jay (2002). The Construction of Evolutionary Theory. Cambridge, MA: Belknap Press.

Krumbiegel, Ingo (1971). Dice Giraffe. Wittenberg (Germany): A. Ziemsen Verlag.

Leuthold, Barbara, and Walter Leuthold (1972). "Nutrient Habits of Giraffe in Tsavo National Park, Kenya," E. Afr. Wildl. J.vol. 10, pp. 129-141.

Pellew, Robin (1984). "The Feeding Ecology of a Selective Browser, the Giraffe (Giraffa camelopardalis tippelskirchi)," J. Zool., London vol. 202, pp. 57-81.

Pincher, Chapman (1949). "Development of the Giraffe," Nature vol. 164, pp. 29-xxx.

Simmons, Robert, and Lue Scheepers (1996). "Winning by a Cervix: Sexual Selection in the Evolution of the Giraffe," The American Naturalist vol. 148, pp. 771-786.

Woolnough, A. P. , and J. T. duToit (2001). "Vertical Zonation of Browse Quality in Tree Canopies Exposed to a Size-Structured Guild of African Browsing Ungulates," Oecologia vol. 129, pp. 585-590.

Young, Truman, and Lynnsebell (1991). "Sex Differences in Giraffe Feeding Ecology: Energetic and Social Constraints," Ethology vol. 87, pp. 79-89.