This latter point, however, is not related specially to the common errors respecting the Darwinian theory which I have indicated above, except in so far as it is a detail of the actual Darwinian theory. I would, in passing, point out that, like the detail referred to in connection with the relationship of the various races of man, this one is not logically deducible from the theory of evolution. In fact, I have sometimes thought that the principal difficulties of that theory arise from this unnecessary and not logically sound doctrine. I pointed out, rather more than three years ago, in an article “On some of our Blood Relations,” in a weekly scientific journal, that the analogy between the descent of races and the descent of individual members of any race, requires us rather to believe that the remote progenitor of the human race and the Simiadæ has had its share—though a less share—in the generation of other races related to these in more or less remote degrees. I may perhaps most conveniently present the considerations on which I based this conclusion, by means of a somewhat familiar illustration:— Let us take two persons, brother and sister (whom let us call the pair A), as analogues of the human race. Then these two have four great-grandparents on the father’s side, and four on the mother’s side. All these may be regarded as equally related to the pair A. Now, let us suppose that the descendants of the four families of great-grandparents intermarry, no marriages being in any case made outside these families, and that the descendants in the same generation as the pair A are regarded as corresponding to the entire order of the Simiadæ, the pair A representing, as already agreed, the race of man, and all families outside the descendants of the four great-grandparental families corresponding to orders of animals more distantly related than the Simiadæ to man. Then we have what corresponds (so far as our illustration is concerned) to Darwin’s views respecting man and the Simiadæ, and animals lower in the scale of life. The first cousins of the pair A may be taken as representing the anthropoid apes; the second cousins as representing the lemurs or half-apes; the third cousins as representing the platyrhine or American apes. The entire family—including the pair A, representing man—is descended also, in accordance with the Darwinian view, from a single family of progenitors, no outside families sharing _descent_, though all share _blood_, with that family.