Interestingly, Darwin believed in the “inherited effects of the increased use of parts” - a very “Larmarckian” view. They form the ancestral stock of the animals that evolve into giraffes. In the case of giraffes, times of drought and arid conditions give an advantage to those animals that can out-compete others by reaching the higher, untouched leaves. These variations become dominant in the species and so it evolves. Natural selection weeds out the unadapted and the best-adapted survive. Under certain environmental conditions particular variations will be most advantageous.
In many respects this is a classic formulation of how Darwin viewed evolution: every species consists of individuals that show considerable variations. By this process long-continued, which exactly corresponds with what I have called unconscious selection by man, combined no doubt in a most important manner with the inherited effects of the increased use of parts, it seems to me almost certain that an ordinary hoofed quadruped might be converted into a giraffe. These will have intercrossed and left offspring, either inheriting the same bodily peculiarities, or with a tendency to vary again in the same manner whilst the individuals, less favoured in the same respects will have been the most liable to perish. Those individuals which had some one part or several parts of their bodies rather more elongated than usual, would generally have survived. So under nature with the nascent giraffe the individuals which were the highest browsers, and were able during dearth to reach even an inch or two above the others, will often have been preserved for they will have roamed over the whole country in search of food. It can thus obtain food beyond the reach of the other Ungulata or hoofed animals inhabiting the same country and this must be a great advantage to it during dearths. The giraffe, by its lofty stature, much elongated neck, forelegs, head and tongue, has its whole frame beautifully adapted for browsing on the higher branches of trees. So Lamarck imagined that over generations the habit of continually reaching for the higher browse produced in the giraffe’s ancestors a lengthening of the legs and neck.Ī little over 60 years later, Charles Darwin commented on giraffe evolution in the sixth edition (1872) of his seminal book, Origin of Species:
these changes give rise to modifications or developments in their organs and the shape of their parts” (p. As Lamarck wrote, “variations in the environment induce changes in the needs, habits and modes of life of living beings. The ancestors of the giraffe - which we should imagine like antelopes or deer - needed to adapt their behavior to this changing environment. In Lamarck’s view, we must imagine a situation in the past where the best food for browsing mammals was higher up in trees, the lower vegetation having been eaten by other animals. From this habit long maintained in all its race, it has resulted that the animal’s 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 six meters. 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 nearly always arid and barren, so that it is obliged to browse on the leaves of trees and to make constant efforts to reach them. One of the first evolutionary thinkers, Jean-Baptist Lamarck, offered a short description of how the giraffe evolved in his major work, Philosophie Zoologique, which was published in 1809: It is as if the giraffe’s long neck was begging to be explained by evolutionary theorists. Once scientists began thinking about animals in terms of evolution, the giraffe became a welcome - and seemingly straightforward - example.
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