SELECTED ARTICLE

          THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE
                                                STOCK*

                                                1. MEAT

                                          JOHN HAMMOND

                                (School of Agriculture, Cambridge)

                           (With Plates XIV—XIX and three text-figs.)

[Reprinted, from the Empire Journal of Experimental Agriculture, Vol. III, No. 9,
                                                January 1935.]

Introduction.—Almost all the characters that are of any importance for
meat (such as weight-for-age and body-proportions) in our farm animals are
dependent for their full expression on environment and nutrition. We cannot,
therefore, consider the genetic characters for meat-production without considering
the environment in which they are developed. In my opinion, most of these
characters have been developed purposely, and their development has been
planned and directed by man through selection in an environment that he has
created to produce them, whilst in only a very small minority of cases have they
arisen, by chance, from large mutations. The large mutations that occur in our
live stock are nearly all of the recessive type, and for the most part consist of
defects and abnormalities or fancy points (such as colour and horns) which are
of little commercial importance. They usually segregate out in simple ratios,
and it is an easy matter to breed for them by using Mendelian methods. On the
other hand, almost all the commercial qualities are ' blending' in inheritance:
there is no dominance, and in my opinion they have been produced by quite a
different method, that is, by the accumulation of small variations, which are conti-
nually appearing, and may be stimulated by the environment. In my opinion,
too, these characters exist in all degrees of ' fixity ' in the animal. In other words,
in terms of present-day explanations, I believe not only in the mutation of a gene
already formed, but also in the possibility of the evolution of a new gene by the
animal itself under the stimulation of the environment, and consequently of
varying degrees of ' fixity ' of characters under environmental change, according
to the state of evolution of the gene in question. Whilst the animal produces
the gene as a mechanism for putting the characters that it has evolved into its
inheritance, a mutation in the gene already fully formed gives a variation in the
animal that is of small importance in evolution, because it is at random and not
purposeful, as in the former case. Thus, I see the real evolution of commercial

* The five papers under this head were read to Section D (Zoology) of the British
Association for the Advancement of Science, Aberdeen, September 10, 1934.

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