Darwin pointed out--and this and no more was Darwin's famous
discovery--that a third explanation, involving neither will nor purpose
nor design either in the animal or anyone else, was on the cards. If
your neck is too short to reach your food, you die. That may be the
simple explanation of the fact that all the surviving animals that feed
on foliage have necks or trunks long enough to reach it. So bang goes
your belief that the necks must have been designed to reach the food.
But Lamarck did not believe that the necks were so designed in the
beginning: he believed that the long necks were evolved by wanting
and trying. Not necessarily, said Darwin. Consider the effect on the
giraffes of the natural multiplication of their numbers, as insisted on
by Malthus. Suppose the average height of the foliage-eating animals is
four feet, and that they increase in numbers until a time comes when all
the trees are eaten away to within four feet of the ground. Then the
animals who happen to be an inch or two short of the average will die
of starvation. All the animals who happen to be an inch or so above
the average will be better fed and stronger than the others.
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