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.