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ON THE OPINION THAT EACH SEX MAT TRANSMIT ANY CHABACTEEISTIC WHATEVER.
The argument from hybrids—This argument is inconclusive— The argument from the homology between the ovum and the male cell—Homology does not involve functional similarity— The argument from the dual personality of each individual; from reversion; and from polymorphism—These phenomena admit of a simpler explanation—Summary of chapter.
The Argument from Hybrids. According to the view to be presented in this work, the functions of the two sexual elements, in inheritance, are not alike.
The proof of this will be presented further on, when the subject is reached in the logical course of the development of our argument.
Some of the very highest authorities have been led to a view which is directly opposite, and have held that either parent may transmit to the offspring any characteristic whatever. Lest any reader should assume, at the beginning of this book, that the work involves an absurdity, and that my conclusion is already disproved, it seems best^tp at once examine the reasons for the opposite view. If I can show that these reasons are inconclusive, and that there is and can bo no proof for the statement that each sexual element transmits to the offspring every characteristic of the parent, we can then enter into the subject without prejudice, and can wait for the proper time to present the proof of the opposite view, that the two sexual elements play different parts in heredity.
If the authority of great names counted for anything whatever in science, the case against me would be very strong, but where an appeal to nature is possible, authority counts for nothing.
Darwin's place among the students of heredity is certainly the highest, and he takes very strong ground indeed upon this subject.
Thus he says (Variation of Animals and Plants, Vol. ii. p. 88): "I am aware that such cases (of prepotency) have been ascribed by various authors to such rules as that the father influences the external characters, and the mother the internal characters.
"But the great diversity of the rules given by various authors almost proves their falseness. Dr. Prosper Lucas has fully discussed this point, and has shown that none of the rules (and I could add others to those quoted by him) apply to all animals. Similar rules have been announced for plants and have been proved by Gartner to be all erroneous."
In the Anatomy of Invertebrated Animals, p. 30, Huxley states that "no structural modification is so slight, and no functional peculiarity is so insignificant in either parent, that it may not make its appearance in the offspring."
Darwin, in many parts of his writings, is still more explicit. Thus he says (Variation of Animals and Plants, Vol. ii. p. 431): "Ovules and the male element, before they become united, have, like buds, an independent existence. Both have the power of transmitting every single character possessed by the parent form. We see this clearly when hybrids are paired inter se, for the characters of either grandparent often reappear, either perfectly or by segments, in the progeny. It is an error to suppose that the male transmits certain characters and the female other characters."
I think a little examination will show clearly the impossibility of proving this statement from the phenomena of crossing. In order to breed together animals must 1)0 closely related; they must belong to the same species or to two closely allied species. Since the individuals which belong to two closely related species are the descendants of a common, and not very remote, ancestral species, it is clear that almost the whole course of their evolution has been shared by them in common; all their generic characteristics being inherited from this ancestor. Only the slight differences in minor points, which distinguish one species of a genus from another, have been acquired since the two diverged, and not even all of these slight differences, for a difference between two allied species may be due to the fact that while one has been modified the other has retained, unmodified, certain resemblances to their common ancestor. We know that the duration of even the most persistent species is only an infinitesimal part of the whole history of their evolution, and it is clear that the common characteristics of two allied species must outnumber, thousands of times, the differences between them. It follows that the parents of any possible hybrid must be alike in thousands of features for one in which they differ. It is therefore out of the question to attempt to prove, from the phenomena of crossing, that each parent can transmit to the child all its characteristics. Crossing simply results in the formation of a germ by the union of a male and a female element derived from two essentially similar parents, with at most only a few secondary and comparatively slight differences, all of which have been recently acquired.
If a perfect animal could be developed from the spermatozoon of a male parent, as it can be, in cases of parthenogenesis, from the ovum of a female parent, we should have a means of proving that each sex transmits its entire organization to its offspring.
The phenomena of parthenogenesis prove that the female does actually thus transmit its entire organization, but there is nothing to show that the male parent does also, for it is clear that, from the nature of the case, the phenomena of crossing are incompetent to prove it.
The Argument from the Homology of the Male and Female Sexual Elements.
Many authors have gone much further than the statement that any characteristic whatever may be transmitted by either parent, and have held that the offspring is actually a dual personality, made up of a complete organization or individuality inherited from the father, and another, equally complete, inherited from the mother. This view has found favor with a number of modern writers, and frequently makes its appearance in the literature of the subject.
Thus Huxley says (Encyclop. Brit., Art. Evolution), "It is conceivable, and indeed probable, that every part of the adult contains molecules derived from the male and from the female parent; and that, regarded as a mass of molecules, the entire organism may be compared to a web, of which the warp is derived from the female, and the woof from the male. And each of these may constitute an individuality in the same sense as the whole organism is one individual, although the matter of the organism has been continually changing."
It will be found, on examination, that there is much to be said in support of this view, although I believe that there is a much simpler explanation of the facts which seem to favor it.
The only reason given by Huxley, in the article above quoted, is the homology between the ovum and the spermatozon; the fact that in all the higher animals and plants the germ is formed by the union of one nucleated cell, the ovum, with another more or less modified nucleated cell, the male cell, and that the structural components of the body of the embryo are all derived, by a process of division, from the coalesced male and female germs.
In answer to this we may point out that while the hypothesis requires that a wasp born from a fertilized egg should differ essentially from one born from a parthenogenetic egg, the one being a dual person and the other a unit, we do not find any obvious difference corresponding to the supposed molecular difference. We should not expect a wasp with a dual personality to be, to all appearances, exactly like one with a single personality.
A fatal objection to Huxley's argument, above given, is that, at bottom, it is simply an assumption that the homology or morphological equivalence of the ovum and male cell proves their functional equivalence. The fallacy of this assumption hardly needs notice, since it is well known that homology is no evidence whatever of functional resemblance. The quill feathers which fit a bird's wing for flight are homologous with the scales which cover and protect the arms and fingers of a crocodile, but we could hardly name two structures which serve more different purposes. The homology between them simply indicates that, at some time in their his