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In this question, the OP uses giraffe necks as a supportive example of evolution. Is the mechanism described in this post accurate? At some point, I thought I remember hearing that giraffes did not evolve long necks to reach higher food resources, but instead longer, stronger necks gave some sort of mating advantage (male competition perhaps?).

Is there a consensus in the scientific community as to evolutionary mechanism(s) that contributed most to the evolution of long necks in giraffes?

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That was Lamark's postulate: – nico Aug 3 '12 at 6:25
up vote 13 down vote accepted

There seems to consensus that it is not competition for tall food. Giraffes actually often feed on resources that are lower than their maximum possible height. See:

Simmons, R. E. & Scheepers, L. 1996. Winning by a Neck: Sexual Selection in the Evolution of Giraffe. The American Naturalist 148: 771–786

This paper put forth the idea that sexual selection is the reason behind long necks. The idea is that longer necked males are dominant. But this theory has also been questioned. See:

G. Mitchell, S. J. Van Sittert, J. D. Skinner. 2009.Sexual selection is not the origin of long necks in giraffes. Journal of Zoology 278, Issue 4: 281–286

So in the end there's no clear consensus. Some papers have returned to the theory of competition for research in the past few years.To put it simply, no there is no consensus.

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Competition for research? Giraffes must be more advanced than I've been giving them credit for! – Richard Smith-Unna Aug 3 '12 at 9:48
Lol, yeah, that's awkwardly worded I suppose. I meant returned to the theory of competition as a topic of research :) – emhart Aug 3 '12 at 20:43

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