Short-Sight in Watchmakers and Engravers
Darwin notices that watchmakers and engravers are liable to be short-sighted, and that short-sight and long-sight certainly tend to be inherited.47 But we must be careful not to beg the question at issue by assuming that the frequent heredity of short sight necessarily covers the heredity of artificially-produced short-sight. Elsewhere, however, Darwin states more decisively that “there is ground for believing that it may often originate in causes acting on the individual affected, and may thence-forward become transmissible.”48 This impression may arise (1) from the facts of ordinary heredity—the ancestral liability being excited in father and son by similar artificial habits, such as reading, and viewing objects closely as among watchmakers and engravers—or by constitutional deterioration from indoor life, &c., acting upon a constitutional liability of the eye to the “something like inflammation of the coats, under which they yield” and so cause shortness of sight by altering the spherical shape of the eye-ball. (2) Panmixia, or the suspension of natural selection, together with altered habits, will account for an increase of short-sight among the population generally. (3) Long-sighted people could not work at watchmaking and engraving so comfortably and advantageously as at other occupations, and hence would be less likely to take to such callings.