I
IT is a familiar fact that offspring resemble their parents on the whole, but differ from them in details. For example, the child of a human being is always another, but never an exactly similar, human being.
These differences in detail are of two sorts, inborn and acquired. Inborn or innate differences arise “by nature”; the child is inherently unlike the parent—taller or shorter, fairer or darker, and so forth. Acquired differences, on the other hand, are due to the conditions under which parents and children have lived. Thus, owing to better or worse surroundings, the child may develop better or worse than the parent and so be taller or shorter, or a greater exposure to weather may render him darker or fairer.
Things We Cannot Inherit
It was formerly believed by scientific men, and is still believed by the public, that traits acquired by the parent tended to be inherited by the child—that is, reproduced as inborn traits. Thus it was supposed that if a man were made strong by exercise, or injured by accident, his child would tend to inherit, in some degree at least, the acquired benefit or injury, and as a result be naturally stronger or more defective than the parent was at the start.
Acquired Traits not Hereditary
But very prolonged and careful investigation has proved that this is certainly an error. For example, though for æons human beings have been learning to speak and walk, and make a multitude of other acquirements, yet none of these are ever inherited. In fact, owing to the evolution of memory and the retrogression of instinct, man, of all animals, acquires the most and inherits the least. Every child has to begin afresh and learn what its ancestors learnt; all are born ignorant; none speak or walk “naturally.” Each starts where the parent began, not where he left off. The parental traits, if reproduced at all, are always of the same kind in the child as in the parents, and appear in the same way. That is, the inborn traits of the parent are always inborn in the offspring; the acquired traits are never anything but acquirements resulting from the same causes as they did in the parent. In brief, the acquirements of the parent are never transmuted into inborn characteristics in the child. They are never inherited. It is admitted on all hands that inborn differences—variations, as they are termed technically—tend to be inherited.
Thus, if the parent is naturally darker than the grandparent, the child tends in colour to resemble the former more than the latter. Since the child may vary from the parent in the same direction as the latter varied from the grandparent, these inborn differences may be accentuated in subsequent generations. It is due to this fact that plant and animal breeders have improved domesticated species. They are able to benefit the individual by improving his surroundings, but the race they can improve only by breeding from the best. In other words, when they have the latter end in view, they must build on natural variations, not on acquirements.
A Great Problem of Science