Darren Naish has a typically wonderful post up about the evolution of giraffe necks, with the delightful snippet that until 1999 people thought they had fewer neck vertebrae than they do.
I can't add to the biology, so allow me to make a few comments about the role of the giraffe in the history of biology.
In the middle ages, the giraffe was known to most Europeans only by travellers' reports, and from classical times it was called the "cameleopard", as it was thought to be a hybrid between a camel, which was a familiar enough animal, at least to the eastern Mediterranean Europeans, and the leopard, which was still in Europe at the beginning of the historical period.
In the nineteenth century, in 1826, a giraffe was offered to the French king, Charles X, by the Pasha of Egypt. It was the first live animal in Europe, and the naturalist Geoffroy Saint-Hilaire was sent to attend it on its path from Marseille to Paris, by the Museum histoire naturelle. Thousands of spectators lined the streets as it walked to Paris, and there began a fashion of all things giraffish, à la giraffe. Geoffroy, the last of the French evolutionists, himself became celebrated, and he and the giraffe died within months of each other, so closely were their respective fates entwined.
But Geoffroy's predecessor, Lamarck, whose theory of evolution was the first that received any attention in the scientific literature, himself made the giraffe something of a celebrated cause. In his Philosophie zoologique in 1809, he had proposed the famous misunderstanding that the long neck was the result of generations of giraffes striving to reach the upper leaves as the lower ones were eaten away, and that this striving caused longer necks to be passed down to progeny, thus gradually accruing the extreme neck of today. This is why Lamarck's view of heredity, which was widely shared at the time, has come to be known as "Lamarckism".
In 1831, Charles Lyell devoted almost an entire volume of his Principles of Geology to Lamarck's views, ironically making Lamarck known in the English speaking world even as he demolished him. The example Lyell chose to discuss at one point was Lamarck's giraffe. And it passed on to subsequent lore that Lamarck's view of evolution was all about organisms "willing" themselves to change. Lamarck himself used the French word besoin, meaning a "want" or "need" - changes were brought about by needs. Lyell used the equally ambiguous English word "want", and hence the misconstrual. Lamarck most certainly did not have the idea that organisms could will their evolution.
A voyaging naturalist named Charles Darwin received that volume en route, and read it thoroughly (no TV on board!). Lyell's discussion of Lamarck's view of species as temporary slices through a temporal sequence of change influenced Darwin to think hard about species (which I will return to in the second post on Darwin and species), and as is well known, Darwin came up with the idea that chance variations would be selected for their ability to make organisms better adapted, thus changing the constitution of a species.
The irony is, as Darren points out, that the adaptive explanation of the giraffe's neck has in recent years been overshadowed by a sexual rather than environment selection explanation - giraffe necks are, it was said, the result of male contests, and female necks followed along with selection for that trait. Now it appears that Darwin was right all along - long necks are feeding adaptations. Thus the circle is complete.
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I notice that if my arm isn't quite long enough to touch an object, I can keep trying to reach and my arm gets longer within a few seconds. Was Lamarck right after all, or should I check around the house for cosmic rays?
Was that the sort of thing that he had in mind? (Not cosmic rays, but the stretching.)
Lamarck's real view was that if there is a need for something, then that will (mechanically; Lamarck was a materialist) cause things to shift in that direction. Your arm stretching is, as I'm sure you know, a matter of ligaments relaxing and muscles deconstricting.
What Lamarck did effectively was conflate individual adaptation (like growing calluses or strong muscles) with taxonomic adaptation. He thought (not unreasonably, given the knowledge of heredity at the time) that these changes in one body would be passed on slightly to the next. Even Darwin thought that the use of a particular trait increased its hereditability, and a disuse decreased it.
But as to the giraffe... If I use my arm to lift heavy objets frequently then muscles will grow to be bulkier. If I don't, they'll decline. Muscles "know" that if they get used then they should bulk up. (Or something like that.)
If we were 18th century biologists then we could speculate that if a limb is frequently stretched then it grows longer, by analogy with muscle. I think it actually won't, not very much, but that's the twenty-first century talking.
So don't we put those together and suppose that giraffes during their lifetime grow longer necks from daily stretching, and chimpanzees longer arms, before passing on the trait to their offspring? (Until an equilibrium is reached, and giraffes crouch as often as they reach.)
Incidentally, do you know if anyone's tried a Lamarckian algorithm in a computer software "genetic algorithm" for problem solving? Software that "learns" - such as the noughts-and-crosses system that discards a move that leads to defeat so as not to play that move again - is doing the half of Lamarckism that Darwinism doesn't do, I propose - but not the mating with other algorithms. You could consider that the stupid program is the ancestor of the smart program as the child is father to the man.
Can Lamarckism be more effective than neo-Darwinian evolution? Or is Lamarckism too "difficult to do", because it requires that a "trait" is recognised and copied back into a genetic coding, whereas dumb DNA just mutates willy-nilly and effectively claims any favourable outcome as a win without trying to decide which genes contributed to success?
For instance, in the United Kingdom, red squirrels are under pressure from two other species - grey squirrels and human beings. Evidently the greys are better at squirrelhood than the reds, but I don't recall hearing of any conservation proposal to trap reds and paint them grey to improve their chances.
And what are the odds on epigenetics proving something? Micro-Lamarckism perhaps? Apparently (from Google) the term has only just been coined, by me.
I recommend reading "The Giraffe's Long Neck: From Evolutionary Fable to Whole Organism" by Craig Holdrege. It has very interesting insights into "scientific" explanatory mechanisms and, one tends to feel, the pointlessness of them all.
For a summary see: www.natureinstitute.org/pub/persp/4/index.htm