In technical language, this is the problem of use-inheritance, otherwise known as the inheritance of acquired characters.  It is apt to seem obvious to the plain man that the effects of use and disuse are transmitted to offspring.  So, too, thought Lamarck, who half a century before Darwin propounded a theory of the origin of species that was equally evolutionary in its way.  Why does the giraffe have so long a neck?  Lamarck thought it was because the giraffe had acquired a habit of stretching his neck out.  Every time there was a bad season, the giraffes must all stretch up as high as ever they could towards the leafy tops of the trees; and the one that stretched up farthest survived, and handed on the capacity for a like feat to his fortunate descendants.  Now Darwin himself was ready to allow that use and disuse might have some influence on the offspring’s inheritance; but he thought that this influence was small as compared with the influence of what, for want of a better term, he called spontaneous variation.  Certain of his followers, however, who call themselves Neo-Darwinians, are ready to go one better.  Led by the German biologist, Weismann, they would thrust the Lamarckians, with their hypothesis of use-inheritance, clean out of the field.  Spontaneous variation, they assert, is all that is needed to prepare the way for the selection of the tall giraffe.  It happened to be born that way.  In other words, its parents had it in them to breed it so.  This is not a theory that tells one anything positive.  It is merely a caution to look away from use and disuse to another explanation of variation that is not yet forthcoming.

After all, the plain man must remember that the effects of use and disuse, which he seems to see everywhere about him, are mixed up with plenty of apparent instances to the contrary.  He will smile, perhaps, when I tell him that Weismann cut off the tails of endless mice, and, breeding them together, found that tails invariably decorated the race as before.  I remember hearing Mr. Bernard Shaw comment on this experiment.  He was defending the Lamarckianism of Samuel Butler, who declared that our heredity was a kind of race-memory, a lapsed intelligence.  “Why,” said Mr. Shaw, “did the mice continue to grow tails?  Because they never wanted to have them cut off.”  But men-folk are wont to shave off their beards because they want to have them off; and, amongst people more conservative in their habits than ourselves, such a custom may persist through numberless generations.  Yet who ever observed the slightest signs of beardlessness being produced in this way?  On the other hand, there are beardless as well as bearded races in the world; and, by crossing them, you could, doubtless, soon produce ups and downs in the razor-trade.  Only, as Weismann’s school would say, the required variation is in this case spontaneous, that is, comes entirely of its own accord.