Posted by Alan Nagel on November 23, 1998 at 17:28:04:
In Reply to: Sidebar: Lamarck and evolution posted by Steve Price on November 23, 1998 at 08:17:04:
Steve's summary is superb. It may bear adding that the mechanisms of evolution must act upon the genetic makeup, and we should not forget that.
The simplest thumbnail version I know would sketch it here that giraffe's with the genes for long necks survive better when, for example, the lower browsing is all consumed by other animals and/or the relatively shorter giraffes during a time of stress (e.g. drought, when there's nothing to graze, and trees are steadily browsed higher and higher, and death by starvation comes into play).
Then there'll be some generations of longer-necked giraffes if the selection has been relatively strong for them, and a possible elimination of short-necked giraffes permanently if the selection is absolutely strong.
This kind of development has recently been demonstrated in very short-term changes in the size of bird-beaks among finches, if I recall correctly, again in the Galapagos islands where Darwin was able to find persuasive evidence for his basic hypotheses, under the conditions of a stressful and tightly bounded ecology.
AFN