Both the work of Karl Pearson and William Bateson represent an important first step in the science of genetics. What these posts hoped to have uncovered is Bateson and Pearson’s philosophical presuppositions that enlightened their scientific work. As we have seen, Pearson’s rejection of a theory of causation and Bateson’s refusal to speculate about the constitution of theoretical entities did have an enormous effect on their scientific outlook. On one hand, Pearson’s notion of association prevented him from accepting the existence of ‘units’ of heredity, and the ultimate rejection of a sort of Mendelism. On the other hand, Bateson’s acceptance of the theoretical entity’s usefulness allowed him to accept the existence of some substance that causes variation in organisms even though we know not what that substance is.
Such an ontological view resembles quite closely what Locke says about substance in his Essay. Locke writes: “The mind being, as I have declared, furnished with a great number of the simple ideas, conveyed in by the senses, as they are found in exterior things, or by reflection on its own operations, takes notice also, that a certain number of these simple ideas go constantly together; which being presumed to belong to one thing, and words being suited to common apprehensions, and made use of for quick dispatch, are called, so united in one subject, by one name: Which, by inadvertency, we are apt afterward to talk of, and consider as one simple idea, which indeed is a complication of many ideas together; because, as I have said, not imagining how these simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum wherein they do subsist, and from which they do result, which therefore we call substance.” II.xxiii.2.; and “These and like fashions of speaking, intimate, that the substance is supposed always some thing besides the extension, figure, solidity, motion, thinking, or other observable ideas, though we know not what it is.” II.xxiii.3 (See Locke 1959).
Bateson inferred that some unobservable theoretical entities exist that cause variation of character traits. Ian Hacking states something close to what Bateson accepts, “as we move down in scale [from the observable] to the truly unseeable, it is our power to use unobservable entities that makes us believe they are there.” Thus, the importance of one’s philosophical presuppositions does impugn upon one’s scientific outlook, no matter how insignificant the assumption seems.