 Lotze next goes on to consider but reject the very old idea that these superficial changes (size and color) have been effected by variations in such environmental factors as habitat or climate. In this supposition, Lotze believes that the central difficulty for all such investigations in this area is an inevitable but nonetheless unsavory dependence upon “uncertain causes of which we can form no conception” (Micro, I, p. 514). Consequently, “the hypothesis of the original unity of the human race cannot be absolutely disproved” (ibid.). The choice between monogenesis and polygenesis remains squarely at the level of scientific conjecture and no one can determine a priori which hypothesis to rule out. What we would prefer is a reliance upon “the actual facts for which we have the evidence of the senses” (Micro, I, p. 524). But even a brief consideration of this data forces upon us the realization that we have, at our disposal, a very small collection indeed.