PROVISIONAL HYPOTHESIS OF PANGENESIS.
PRELIMINARY REMARKS.
FIRST PART:
THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY, THE VARIOUS
KINDS OF REPRODUCTION.
REGROWTH OF AMPUTATED PARTS.
GRAFT-HYBRIDS.
THE DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE.
DEVELOPMENT.
THE FUNCTIONAL INDEPENDENCE OF THE UNITS OF THE BODY.
VARIABILITY.
INHERITANCE.
REVERSION.
SECOND PART:
STATEMENT OF THE HYPOTHESIS.
HOW FAR THE NECESSARY ASSUMPTIONS ARE IMPROBABLE.
EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF FACTS SPECIFIED
IN THE FIRST PART.
CONCLUSION.
In the previous chapters large classes of facts, such as those bearing on bud-
variation, the various forms of inheritance, the causes and laws of variation,
have been discussed; and it is obvious that these subjects, as well as the
several modes of reproduction, stand in some sort of relation to one another.
I have been led, or rather forced, to form a view which to a certain extent
connects these facts by a tangible method. Every one would wish to explain to
himself, even in an imperfect manner, how it is possible for a character
possessed by some remote ancestor suddenly to reappear in the offspring; how
the effects of increased or decreased use of a limb can be transmitted to the
child; how the male sexual element can act not solely on the ovules, but
occasionally on the mother-form; how a hybrid can be produced by the union of
the cellular tissue of two plants independently of the organs of generation;
how a limb can be reproduced on the exact line of amputation, with neither too
much nor too little added; how the same organism may be produced by such
widely different processes, as budding and true seminal generation; and,
lastly, how of two allied forms, one passes in the course of its development
through the most complex metamorphoses, and the other does not do so, though
when mature both are alike in every detail of structure. I am aware that my
view is merely a provisional hypothesis or speculation; but until a better one
be advanced, it will serve to bring together a multitude of facts which are at
present left disconnected by any efficient cause. As Whewell, the historian of
the inductive sciences, remarks:--"Hypotheses may often be of service to
science, when they involve a certain portion of incompleteness, and even of
error." Under this point of view I venture to advance the hypothesis of
Pangenesis, which implies that every separate part of the whole organisation
reproduces itself. So that ovules, spermatozoa, and pollen-grains,--the
fertilised egg or seed, as well as buds,--include and consist of a multitude
of germs thrown off from each separate part or unit. (27/1. This hypothesis
has been severely criticised by many writers, and it will be fair to give
references to the more important articles. The best essay which I have seen is
by Prof. Delpino, entitled 'Sulla Darwiniana Teoria della Pangenesi, 1869' of
which a translation appeared in 'Scientific Opinion' September 29, 1869 and
the succeeding numbers. He rejects the hypothesis, but criticises it fairly,
and I have found his criticisms very useful. Mr. Mivart ('Genesis of Species'
1871 chapter 10.) follows Delpino, but adds no new objections of any weight.
Dr. Bastian ('The Beginnings of Life' 1872 volume 2 page 98) says that the
hypothesis "looks like a relic of the old rather than a fitting appanage of
the new evolution philosophy." He shows that I ought not to have used the term
"pangenesis," as it had been previously used by Dr. Gros in another sense. Dr.
Lionel Beale ('Nature' May 11, 1871 page 26) sneers at the whole doctrine with
much acerbity and some justice. Prof. Wigand ('Schriften der Gesell. der
gesammt. Naturwissen. zu Marburg' b. 9 1870) considers the hypothesis as
unscientific and worthless. Mr. G.H. Lewes ('Fortnightly Review' November 1,
1868 page 503) seems to consider that it may be useful: he makes many good
criticisms in a perfectly fair spirit. Mr. F. Galton, after describing his
valuable experiments ('Proc. Royal Soc.' volume 19 page 393) on the
intertransfusion of the blood of distinct varieties of the rabbit, concludes
by saying that in his opinion the results negative beyond all doubt the
doctrine of Pangenesis. He informs me that subsequently to the publication of
his paper he continued his experiments on a still larger scale for two more
generations, without any sign of mongrelism showing itself in the very
numerous offspring. I certainly should have expected that gemmules would have
been present in the blood, but this is no necessary part of the hypothesis,
which manifestly applies to plants and the lowest animals. Mr. Galton, in a
letter to 'Nature' (April 27, 1871 page 502), also criticises various
incorrect expressions used by me. On the other hand, several writers have
spoken favourably of the hypothesis, but there would be no use in giving
references to their articles. I may, however, refer to Dr. Ross' work, 'The
Graft Theory of Disease; being an application of Mr. Darwin's hypothesis of
Pangenesis' 1872 as he gives several original and ingenious discussions.)
In the First Part I will enumerate as briefly as I can the groups of facts
which seem to demand connection; but certain subjects, not hitherto discussed,
must be treated at disproportionate length. In the Second Part the hypothesis
will be given; and after considering how far the necessary assumptions are in
themselves improbable, we shall see whether it serves to bring under a single
point of view the various facts.