ORIGINAL ARTICLES

                  HEREDITY AND DISEASE RESISTANCE

                                                BY

                 PROF. F. A. E. CREW, M.D., D. Sc., PH.D.

    Director, Imperial Bureau of Animal Genetics, University of Edinburgh.

               (Received for publication on 10th January, 1938)

OBSERVATION and experiment have shown clearly and conclusively that
constant and true-breeding differences in resistance to particular diseases
distinguish the species and that in all probability such differences are paralleled
by differences which distinguish individuals of one and the same species.
This is as would be expected by the geneticist. It is indeed safe to assert
that such resistance and susceptibility are genetic, in whole or in part, and
that natural selection would tend to eliminate the susceptible and produce
a population more resistant than one which had not been subjected to such
natural selection.

Granting this it follows that the genetic improvement of an animal popula-
tion is stopped by any measures that prevent selection. Prophylaxis and
therapy must necessarily prevent genetic improvement in respect of resistance
because the less resistant are saved to reproduce.

There can be little doubt that the resistance of an individual host to a
given infection is determined largely by genetic factors but the value and the
nature of these factors have not yet been disclosed. We do not know how
these factors produce their effects, whether they are specific or non-specific,
and we do not know whether such resistance is uni- or multi-factor in its origin.
Experiment has shown that between strains of the same species there are
differences in mortality from specific infections which are to be referred to
genetic differences between the strains. Selective breeding within the strain
on the other hand has yielded results which lack uniformity. If resistance

NOTE.—It should be explained that the above note by Prof. F. A. E. Crew was
not written for publication but for the purpose of taking part at a discussion
on "Heredity and Disease Resistance," held at the Jubilee Session of the Indian
Science Congress, Calcutta, 1938. In view of the importance of the subject his
permission has, however, been obtained to publish it as it stands. The feasibility
of breeding disease-resistant strains of domesticated animals is a matter regard-
ing which there has been considerable difference of opinion and the clear expres-
sion of opinion contained in this note, by such an authority as Professor Crew,
should help to clarify the position.—[ Ed. ]

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