Correlation.

The term “correla­tion” is somewhat scornfully said by Weismann to be “unquestionably a fine word,” and it has indeed in biological writings a very varied set of meanings. I will not vex the reader with a reference to our old friend Mesopotamia, but mention what Dr. Vernon in Variation in Animals and Plants says of the term, referring to the relation between stature and head-index in man: “Such a statement must vary according to the notion of the observer as to what does and what does not constitute correla­tion.”[35] The most approved and precise meaning of the loose term in question is that associated with the work of the biometricians, and a few examples from Dr. Vernon’s book will show how far this concep­tion of correla­tion is removed from the literal applica­tion of Professor Thomson’s formula. Dr. Vernon treats of such phenomena as the correla­tion of the long heads of greyhounds with length of legs, contrasting them with the shortened heads and legs of bull-dogs. He describes also the correla­tion in man between the stature and length of forearm from elbow to tip of middle finger, correlated measurements of crabs, of external structures of prawns, the tufts of Polish fowls correlated with perforations in the skull, also certain constitutional peculiarities with colour of skin. These few cases are enough to give an idea of the more precise and fairer accepta­tion of the term, but while these form a useful subject for minute study it may be remarked that they agree also with Lamarckian factors as to their origin and development. They are much more in line with Darwin’s use of the word and are strangely reminiscent of the well-known example of the Irish elk with its great head and horns which was brought forward in favour of Lamarckism by Herbert Spencer. They breathe an atmosphere of physiology rather than anatomy, or function than form.

Enough has been said here by way of defining the terms of the issue. The negative we have to sustain is that the following facts and observations declare that certain small modifications cannot be governed by selection and are not correlated with useful characters. It will be shown later that Professor Thomson’s stringent condition is not in all of them compiled with, but that, in spite of this, the probability of their being valid examples of Lamarckism in practice is immense.

CHAPTER IV.
INITIAL VARIATIONS AND TOTAL EXPERIENCE.

The present chapter is on a priori lines and will perhaps be dismissed with a wave of the hand or hurriedly skimmed over, but I pray the reader at least to read the two or three last pages of it. It is at any rate suggestive, and perhaps I may anticipate the comments of the neo-Darwinian and throw myself on his mercy by mentioning a remark of the late Sir Andrew Clark, prince of physicians and genial cynic, which he made to a patient in my presence. A lady not distinguished for depth of thought asked him a rather silly question in medicine. As if offended he drew himself up, holding in his hand a cup of tea which he was enjoying, and replied at once “Madam, you must get a younger and more inexperienced man than I am to answer you that question.”

A very high degree of probability may be attached to the presupposi­tion that Lamarckian factors, even in their humblest form, may enter into the story of the organisms as historical and living beings. Every hypothesis in matters of science, or, to put it at its lowest, every scientific guess must transcend the evidence at the time available.