Johanssen wished to discern the phenotype from the genotype (Johannsen, 1909). “Genes,” however, became what geneticists concluded Mendelian Faktoren had been. Were genes hypothetical constructs, autonomous structural entities or loci of differential functional emphases along an integral chromosome? Or, did all that not matter and genes were simply intervening variables, helpful entities for experimental work (see Chapter 4)?

Strictly speaking, there are no hypothesis-free concepts, and the distinctions between hypothetical constructs and intervening variables that proved very helpful historiographically, are more problematic when one attempts to apply them to personal conceptions. Whether we wish it or not, our concepts “are constructions in thought representing historically an immense amount of intellectual work … the scientific hypothesis does not come after the numerical data but before them” (Woodger, 1967, 366). Morgan, like Johannsen, insisted on presenting genes as intervening variables, with no hypothesis about the nature of the “something.” As late as in his Nobel talk he asserted: