So I beg of you to remember that while the fact and law of heredity is as certain as death itself, its course of action, its variability of operation, is as the March winds. To say that the constitutions of your children will be de* termined in great part by the condition of your body and mind is but to utter a truism; but to say exactly how—in what given channel this effect will flow—is not, in the present state of biological knowledge, possible.
For the sake of illustration it is usually the part of wisdom to give the most probable trend of a given disorder; but to assert dogmatically that the son of a lunatic will be insane or that the daughter of a woman of the street will live as her mother did, is quite as unsafe as to say that a fall from a fourth-story window on to an iron door would be certain death. You must not forget that you may, if you want to take the chances, drop an infant out of a fourth-story window on to an iron door with no bad results to the infant (door not heard from), for I have known that to happen; you may sleep with a bad case of small-pox and not take it—as I once did; you may shoot a ball into a boy's head, taking in with it several pieces of bone, you may extract the bone and leave the ball there and the boy appear to be as good as new afterward; you may live all your life long with a roue and your children not be inmates of hospital, lunatic asylum or prison. All these things have been done, but it is not the part of wisdom to infer that for this reason either one of them would be a safe or desirable course of action; for in this world it behooves us to deal—when we are attempting to study nature—with the law of probability. The accidents, the exceptions, will take care of themselves.
Notwithstanding this fact it will not be exactly fair to me for you to report that I say that every single one of Jane Smith's children will have fits and fall in the fire before they are twenty-one because she or their father is an epileptic. Perhaps one or two of those children may die in infancy, instead, or go insane—or to Congress; one may have hydrocephalus, and another be a moral idiot and astonish the natives because "His parents were such upright people." One may simply have a generally weak constitution—and another may win the American cup for wrestling; but the chances are that confirmed epilepsy (or what not) of the parent is going to "tell" in one form or another in the children. What I say of epilepsy is equally true of syphilis. This latter is so true that it can be readily told by the teeth of the children of a seriously infected case. That will strike the average "unprofessional" reader as impossible, yet it is well known to biologists, medical men and many dentists, so that a great many wholly innocent people who sit in a dentist's chair reveal more private family history than could be drawn from them with stronger instruments than mere forceps.
I have been asked to write this paper because at the present time there is a tendency to discredit some of the well-known and easily proven facts of heredity, as a result of certain statements supposed to have been made by the recent school of biologists headed by Weismann. But in the hands of the laity much that Weismann did say is misunderstood and misstated and much that he never said is inferred. To professional biologists the loose inferences from Weismann's suggestions and speculations are absurd, and to experienced medical men and experts in the lines of practice indicated above, the arguments are beneath discussion. It is in this particular line of practice that proof is easy and abundant, where the "acquired" nature of the modified "character" is readily traced and the transmission (or heredity) susceptible of proof beyond controversy.
It is for this reason that the illustrations are all taken from this field of investigation. If they were taken from consumption, tuberculosis or any of the various ordinary "transmittible" disorders, the cheerful opponent would assert (and no one could disprove if he held to the "germ plasm" theory back far enough) that the "tendency" had been inherent in the plasm since the days of "Adam"—that it was not an "acquired" character or condition which was transmitted. But with artificially produced epilepsy (either by accident or purposely as in the cases of Brown-Sequard's guinea pigs) or in the other so frequent and so frightful disorder mentioned above, it is a simple matter to trace the "acquirement" as well as the transmission. But when a new light arises in the literary or scientific world there are always many persons ready to spring forth with the declaration that they agree with the new point of view without first taking the precaution to ascertain what the recent theory really is. "Oh, I agree with him, the old theory is quite dead," greets the ear, and the placid pupils of the rising light so warp and distort the real opinion of the master as to make of him an absurdity. This has been markedly true of Weismann and his theory of heredity.
In ordinary cases of scientific discussion the misconceptions of the laity would soon adjust themselves and little or no harm would be done meantime; but in such a problem as the present far more is involved than appears upon the surface. The ethical and moral results—not to mention the physical—of a reckless mistranslation or misconception of a scientific theory of this nature cannot be readily estimated, nor can it be confined to one generation. It is pathetic to realize that many fairly well-educated and well-meaning people, who would protect with their lives the children they give to the world and shield them against all possible physical, moral or mental distortion, mutilation or deformity, will stamp upon those children far worse mutilations and distortions (and even physical disorders) through and because of a half-understood version of u the new theory of heredity. Therefore I repeat that so far as the public is concerned, so far as the sociological features of the problem of heredity are involved, so far as the new theory relates to conduct and to physical and mental condition and their transmission, this controversy belongs to the laboratory—to the how and not to the fact of hereditary transmission, as I trust the above illustrations (which might be multiplied a thousand times) will serve to show.
ENVIRONMENT: CAN HEREDITY BE MODIFIED
But heredity is not the whole story, any more than the foundation is the whole house.
Several times when I have spoken or written upon the basic principle of heredity, I have been met by questions like this: "Then you must think it is hopeless. With these awful facts and illustrations of the power and persistence of heredity before us, we must recognize that we are doomed before we are born, must we not? If there is, as you say, no escape from our heredity and its power and influence, what is the use of trying? Why not let go and just drift on the tide of inherited conditions? If these conditions are unfortunate for us, why not just accept the tragedy; if favorable, drift in the sunlight that our ancestors turned upon us, and let the world wag as it will?—we are not responsible." I confess that each time this sort of reasoning comes to me it finds me in a state of surprise that it is possible for thoughtful people—and naturally those are the ones interested in reading or talking upon the subject—I confess it surprises me anew each time to find that it is possible for such people to reason so inadequately and to see with but one eye.