On the rediscovery and confirmation of Mendel’s Law by de Vries,
Correns, and Tschermak two years ago, it became clear to many
naturalists, as it certainly is to me, that we had found a principle
which is destined to play a part in the Study of Evolution comparable
only with the achievement of Darwin--that after the weary halt of forty
years we have at last begun to march.
If we look back on the post-Darwinian period we recognize one notable
effort to advance. This effort--fruitful as it proved, memorable as it
must ever be--was that made by Galton when he enuntiated his Law of
Ancestral Heredity, subsequently modified and restated by Karl Pearson.
Formulated after long and laborious inquiry, this principle beyond
question gives us an expression including and denoting many phenomena
in which previously no regularity had been detected. But to practical
naturalists it was evident from the first that there are great groups
of facts which could not on any interpretation be brought within the
scope of Galton’s Law, and that by no emendation could that Law be
extended to reach them. The existence of these phenomena pointed to a
different physiological conception of heredity. Now it is precisely
this conception that Mendel’s Law enables us to form. Whether the
Mendelian principle can be extended so as to include some apparently
Galtonian cases is another question, respecting which we have as yet no
facts to guide us, but we have certainly no warrant for declaring such
an extension to be impossible.
Whatever answer the future may give to that question, it is clear from
this moment that every case which obeys the Mendelian principle is
removed finally and irretrievably from the operations of the Law of
Ancestral Heredity.
At this juncture Professor Weldon intervenes as a professed exponent
of Mendel’s work. It is not perhaps to a devoted partisan of the Law
of Ancestral Heredity that we should look for the most appreciative
exposition of Mendel, but some bare measure of care and accuracy in
representation is demanded no less in justice to fine work, than by the
gravity of the issue.
Professor Weldon’s article appears in the current number of
_Biometrika_, Vol. I. Pt. II. which reached me on Saturday, Feb. 8.
The paper opens with what purports to be a restatement of Mendel’s
experiments and results. In this “restatement” a large part of Mendel’s
experiments--perhaps the most significant--are not referred to at
all. The perfect simplicity and precision of Mendel’s own account are
destroyed; with the result that the reader of Professor Weldon’s paper,
unfamiliar with Mendel’s own memoir, can scarcely be blamed if he fail
to learn the essence of the discovery. Of Mendel’s conception of the
hybrid as a distinct entity with characters proper to itself, apart
from inheritance--the most novel thing in the whole paper--Professor
Weldon gives no word. Upon this is poured an undigested mass of
miscellaneous “facts” and statements from which the reader is asked
to conclude, first, that a proposition attributed to Mendel regarding
dominance of one character is not of “general”[52] application, and
finally that “all work based on Mendel’s method” is “vitiated” by a
“fundamental mistake,” namely “the neglect of ancestry[53].”
[52] The words “general” and “universal” appear to be used by
Professor Weldon as interchangeable. Cp. Weldon, p. 235 and
elsewhere, with Abstract given below.
[53] These words occur p. 252: “The fundamental mistake which
vitiates all work based upon Mendel’s method is the neglect of
ancestry, and the attempt to regard the whole effect upon offspring
produced by a particular parent, as due to the existence in the
parent of particular structural characters, &c.” As a matter of fact
the view indicated in these last words is especially repugnant to the
Mendelian principle, as will be seen.
To find a parallel for such treatment of a great theme in biology we
must go back to those writings of the orthodox which followed the
appearance of the “Origin of Species.”
On 17th December 1900 I delivered a Report to the Evolution Committee
of the Royal Society on the experiments in Heredity undertaken by Miss
E. R. Saunders and myself. This report has been offered to the Society
for publication and will I understand shortly appear. In it we have
attempted to show the extraordinary significance of Mendel’s principle,
to point out what in his results is essential and what subordinate, the
ways in which the principle can be extended to apply to a diversity
of more complex phenomena--of which some are incautiously cited by
Professor Weldon as conflicting facts--and lastly to suggest a few
simple terms without which (or some equivalents) the discussion of such
phenomena is difficult. Though it is impossible here to give an outline
of facts and reasoning there set out at length, I feel that his article
needs an immediate reply. Professor Weldon is credited with exceptional
familiarity with these topics, and his paper is likely to be accepted
as a sufficient statement of the case. Its value will only be known to
those who have either worked in these fields themselves or have been at
the trouble of thoughtfully studying the original materials.
The nature of Professor Weldon’s article may be most readily indicated
if I quote the summary of it issued in a paper of abstracts sent out
with Review copies of the Part. This paper was most courteously sent to
me by an editor of _Biometrika_ in order to call my attention to the
article on Mendel, a subject in which he knew me to be interested. The
abstract is as follows.
“Few subjects have excited so much interest in the last year or two
as the laws of inheritance in hybrids. Professor W. F. R. Weldon
describes the results obtained by Mendel by crossing races of Peas
which differed in one or more of seven characters. From a study of
the work of other observers, and from examination of the ‘Telephone’
group of hybrids, the conclusion is drawn that Mendel’s results
do not justify any general statement concerning inheritance in
cross-bred Peas. A few striking cases of other cross-bred plants and
animals are quoted to show that the results of crossing cannot, as
Mendel and his followers suggest, be predicted from a knowledge of
the characters of the two parents crossed without knowledge of the
more remote ancestry.”