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.
A variety of other studies show
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
usually feed from bushes at or below shoulder height (about two
and one half meters in females and three meters in males). Fifty
percent 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;
see Figure 2). During the rainy season, when there is abundant
browse at all levels, giraffes are more likely to feed from the
higher branches, browsing fresh, protein-rich leaves. Other
studies also show that giraffes do most of their feeding at about
shoulder height, with their necks positioned nearly horizontally
(Young and Isbell 1991; Woolnough and du Toit 2001). So it looks
as though giraffes are not using their long necks the way the
theory demands. And they use them even less to reach heights in
the dry season, when the theory demands they should need them
4) There are other ways to reach
the high foliage of trees. Goats, for example, are known to climb
into trees and eat foliage (see Figure 3). Why didn't
tree-climbing leaf-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, often
stands on its hind limbs and browses, reaching heights of two
meters and more. The much larger and heavier elephant even stands
sometimes on its back legs and extends its trunk to reach high
limbs—but no one thinks that the elephant developed its
trunk as a result of selection pressures to reach higher food.
In sum, there is nothing in this
theory that shows a compelling link between leg and neck
lengthening and feeding on high limbs. Just because giraffes have
long necks and long legs and can reach food high in the
trees does not mean that a need to reach high browse was a
causative factor in the evolution of those characteristics.
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.)
Clearly, both Darwin's and
Lamarck's conceptions of giraffe evolution were highly
speculative. The idea that giraffes developed longer legs and
necks to reach higher food seems plausible, even compelling, as
long as we do not (1) think the idea through in all its
implications and (2) take into account essential observations of
giraffe behavior and ecology. In the end, the idea is neither
logically compelling nor based on fact.
Alternative Explanatory Attempts
Pincher (1949), after critiquing
Darwin's explanation, suggests that the "most extraordinary
feature of the giraffe is not the length of the neck but the
length of the forelegs." By developing long legs, the giraffe
has acquired a huge stride so that it can move relatively fast for
its size. This has left the giraffe with only one predator—the
lion. Pincher therefore explains the "excessive length of its
forelegs as the effect of natural selection acting continually
through the hunter-hunted relationship, as in the case of hoofed
mammals generally." The neck, in turn, followed the
lengthening legs so that the giraffe could still reach the ground
It is strange that Pincher is able
to critique Darwin's view so clearly and yet 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 running muscles, both of which would have aided in avoiding
predators. The fact is that despite its size and long stride, the
giraffe is still preyed upon by lions. And as one study of one
hundred giraffes killed by lions in South Africa showed, almost
twice as many bulls were killed as cows (Pienaar 1969; cited in
Simmons and Scheepers 1996). The longer stride of bulls evidently
doesn't help them avoid lions better than the shorter legged
females. Who knows whether their long stride may in some way make
them more vulnerable? Another speculative idea into the
Brownlee (1963) speculates that
the lengthening of the limbs and neck in the giraffe give the
giraffe a relatively large surface area, which should allow it to
dissipate heat. This would be of advantage in the hot tropical
climate, so that the tendency toward lengthening would have been
encouraged by natural selection, since the largest animals would
have been best able to survive heat waves.
As in the other suggested
"explanations," the central question is, Is Brownlee's
idea rooted in reality? Because of its long legs and neck, the
giraffe appears to have a large surface area. But surface area
alone is not important; it is the relation of the heat producing
volume to surface area that is crucial. A small animal has a small
volume in relation to a very large surface area, while a large
animal very large volume in relation to its relatively small
Now 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 blood vessels, would
act to enlarge the surface-to-volume ratio substantially.
Krumbiegel (1971) estimates that the ratio of volume to surface in
the giraffe is 11:1, compared, say, to a smaller, long-necked
antelope, the gerenuk, which has a ratio of 4.7:1 (similar to the
human). In other words, despite appearances, the giraffe still has
a very large volume in relation to its surface area and its unique
form provides no grounds to think that it evolved in relation to
More 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 point 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 large, 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 frequently. Since long-necked males mate more
frequently, selection works in favor of long necks. This would
also help explain why males have not only absolutely longer, but
proportionately heavier heads than females.
This hypothesis seems consistent
with the difference between male and female giraffes. At least it
gives a picture of how the longer neck of males can be maintained
in evolution. But it doesn't tell us anything about the origin of
neck lengthening in giraffes per se—the neck has to reach a
length of one or two meters to be used as 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
can only speculate that female neck 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 Have a Long Neck?
All the above explanations of the
evolution of the giraffe's long legs and long neck are
unsatisfying. Each of the authors sees problems in other
explanations, but remains within the same explanatory framework
when putting forward his own 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 area) and consider
them in isolation from the rest of the organism. The individual
feature is then placed into relation to one purported
causal factor in the environment (drought, heat, predator
avoidance, male competition). The link of individual feature to
environmental factor is supposed to explain the evolution of that
But this is a highly problematic
procedure. The giraffe's neck carries out a variety of
functions—it allows feeding from high branches, serves as a
weapon in males, brings the head to elevated heights that give the
giraffe a large field of view, is used as a pendulum while
galloping, and so on. Virtually all structures and organs in the
animal 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 be inadequate.
This is comparable to believing you can paint a richly-nuanced,
colorful rendition of a landscape with one color. It just does not
Figure 4. "Short-necked"
giraffes grazing. Giraffes can only reach the ground with their
mouths to drink or graze by splaying their front legs (left) or
splaying and bending their forelegs (right). (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 short neck.
If you observe a giraffe drinking or, as they occasionally do,
grazing close to the ground, then you know what I mean (see Figure
4). Giraffes do not drink often, but when they do, they have to
either splay their forelegs to the side or bend their forelegs
strongly at the wrist joint. Both procedures take time and are
awkward for the giraffe. But only in this way can it get the tip
of its mouth 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 reach the ground without bending their legs,
and the long-legged elephant has its trunk to compensate for its
short neck. Only the giraffe (and its rain forest relative, the
Okapi) have necks that are so 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 manifestly short neck? Why don't we have
evolutionary hypotheses explaining how the giraffe got its short
neck? It is because the giraffe's 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
torso. We 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, short-necked drinking giraffe
appears as exceptional, almost unfortunate behavior.
Whether the neck is long or short
depends on our perspective and on the behavioral or anatomical
context we are focusing on. We only understand the giraffe when we
view it from various perspectives and let the giraffe show
different aspects of its being. The moment we focus solely on the
"long neck"—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 explanation may be coherent and logical, but
what it explains is not the thing itself but a specter of it—the
isolated aspect that has been abstracted from the whole organism.
In reality, the organism as a whole evolves; all its parts are
multifunctional, facilitating its interactions with its complex,
changing environment. It we don't consider all partial aspects
within this larger context, we can only have inadequate
explanations void of life.
Another consequence of the usual
way of explaining is that the organism itself is atomized into
individual characteristics, each having its own explanation. Each
part takes on a quasi-reality of its own, 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.
In sum: the whole project of
explaining the evolution of an animal by abstracting from the
whole leads to unsatisfying, speculative ideas on the one hand,
and to conceptual dissolution of the unity of the organism on the
other. A more adequate understanding requires that we first
investigate the organism as a whole and how its members
interrelate and interact within the context of the whole organism
and its environment. This holistic understanding can then form the
starting point for thinking about the evolution of the
animal. The evolutionary biologist Dobzhansky's famous statement
that "nothing in biology can be understood except in light of
evolution" is a grand claim, which I believe is, in the end,
true. But we have a lot of work to do before we get there, and we
should not be satisfied with short-cut evolutionary
If evolutionary thought is to have
a solid foundation, we must establish this firm grounding in
holistic understanding. As it is, stories of the evolution of
traits seem compelling 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 be no more than a tall story."
for the sake of explanation a spherical body, the two-dimensional
surface grows as a function of the square of the radius, while the
volume—being three-dimensional—grows as a function of
the cube of the radius. A sphere with a radius of 2.5 cm (1 inch)
has a volume-to-surface ratio of 0.8:1. A much larger sphere with
a radius of 50 cm (about 20 inches) has a volume-to-surface ration
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Original source: In Context #10 (Fall, 2003, pp.
14-19); copyright 2003 by The Nature Institute