Typical laws of heredity / Francis Galton.

  • Galton, Francis, 1822-1911.
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Typical laws of heredity / Francis Galton. Source: Wellcome Collection.

    10/22 (page 8)
    8 Жг. Francis Galton [Féb. 9, to their stature and marched up to the wall, each man of them would find the chalked line which he saw opposite to him to be of exactly his own height. So far as I can judge from the run of the figures in the table, the error would never exceed a quarter of an inch, except at either extremity of the series. The principle of the law of deviation is very simple. The im¬ portant influences that acted upon each pellet were the same ; namely, the position of the point whence it was dropped, and the force of gravity. So far as these are concerned, every pellet would have pursued an identical path. But in addition to these, there were a host of petty disturbing influences, represented by the spikes among which the pellets tumbled in all sorts of ways. The theory of combination shows that the commonest case is that where a pellet falls equally often to the right of a spike as to the left of it, and therefore drops into the compartment vertically below the point where it entered the harrow. It also shows that the cases are very rare of runs of luck carrying the pellet much oftener to one side than the other of the successive spikes. The law of deviation is purely numerical ; it does not regard the fact whether the objects treated of are pellets in an apparatus like this, or shots at a target, or games of chance, or any other of the numerous groups of occurrences to which it is or may be applied.* I have now done with my description of the law. I know it has been tedious, but it is an extremely diflicult topic to handle on an occasion like this. I trust the application of it will prove of more interest. First, let me point Out a fact which Quetelet and all writers who have followed in his path have unaccountably overlooked, and which has an intimate bearing on our work to-night. It is that, although characteristics of plants and animals conform to the law, the reason of their doing so is as yet totally unexplained. The essence of the law is that differences should be wholly due to the collective actions of a host of independent petty influences in various combinations, which were re¬ presented by the teeth of the harrow, among which the pellets tumbled in various ways. -Now the processes of heredity that limit the number of the children of one class, such as giants, that diminish their resem¬ blance to their fathers, and kill many of them, are not petty influences, but very important ones. Any selective tendency is ruin to the law of deviation, yet among the processes of heredity there is the large influence of natural selection. The conclusion is of the greatest im¬ portance to our problem. It is, that the processes of heredity must work harmoniously with the law of deviation, and be themselves in some sense conformable to it. Each of the processes must show this conformity separately, quite irrespectively of the rest. It is not an ♦ Quetelet, apparently from habit rather than theory, always adopted the binomial law of error, basing his tables on a binomial of high power. It is abso¬ lutely necessary to the theory of the present paper to get rid of binomial limitations and to consider the law of deviation or error in its exponential form.