Darwin quotes some cases from Dr. Prosper Lucas's "long" but weak and
unsatisfactory "list of inherited injuries."[62] But Lucas was somewhat
credulous. One of his cases is that many girls were born in London
without mammae through the injurious effect of certain corsets on the
mothers. He also gives a long account of a Jew who could read through
the thick covers of a book, and whose son inherited this "hyperaesthesia"
of the sense of sight in a still more remarkable degree (i. 113-119).
Evidently Lucas's cases cannot be accepted without some amount of
reserve.
The cases of the three calves which inherited the one-horned condition
of the cow, the two sons who inherited a father's crooked finger, and
the two sons who were microphthalmic on the same side as their father
had lost an eye, may be due to mere coincidence; or an inherited
constitutional tendency or liability might lead to somewhat similar
results in parent and offspring[63]--just as the tendency to certain
fatal diseases or to suicide may produce similar results in father and
son, although the artificially-produced hanging or apoplexy obviously
cannot be directly transmitted. That more than one of the offspring was
affected does not render the chances against coincidence "almost
infinitely great," as Darwin mistakenly supposes. It "frequently occurs"
that a man's sons or daughters may _all_ exhibit either a latent or a
newly-developed congenital peculiarity previously unknown;[64] and the
coincidence may merely be that one of the parents accidentally suffered
a similar kind of injury--a kind of coincidence which must of course
occasionally occur, and which may have been partly caused by a latent
tendency. The chances against coincidence are indeed great, but the
cases appear to be correspondingly rare.
Darwin acknowledges that many supposed instances of inherited mutilation
may be due to coincidence; and there is apparently no more reason for
attributing inherited scars, &c., to any special form of heredity than
to the effect of the mother's imagination on the unborn babe--a popular
but fallacious belief in corroboration of which far more alleged
instances could be collected than of the inheritance of injuries.
As an instance of the coincidences that occur, I may mention that a
friend of mine has a daughter who was born with a small hole in one ear,
just as if it were already pierced for the earring which she has since
worn in it. I suppose, however, that no one will venture to claim this
as an instance of the inheritance of a mutilation practised by female
ancestors, especially as such holes are not altogether unknown or
inexplicable, though very rarely occurring low down in the lobe of the
ear.[65]
Many cases are known of the inheritance of mutilations or malformations
arising congenitally from some abrupt variation in the reproductive
elements. In such cases as the one-eared rabbits, the two-legged pigs,
the three-legged dogs, the one-horned stags, hornless bulls, earless
rabbits, lop-eared rabbits, tailless dogs, &c., if the father or the
mother or the embryo had suffered from some accident or disease which
might plausibly have been assigned as the cause of the original
malformation, these transmitted defects would readily be cited as
instances of the inheritance of an accidentally-produced modification.
The inheritance of exostoses on horses' legs may be the inheritance of a
constitutional tendency rather than of the effect of the parents' hard
travelling. Horses congenitally liable to such formations would transmit
the liability,[66] and this might readily be mistaken for inheritance of
the results of the liability. An apparent increase in this liability
might arise from greater attention being now paid to it, or from
increased use of harder roads; or a real increase might be due to
panmixia and some obscure forms of correlation.