Part 2

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I venture to express the conviction, that if the facts now before us are carefully studied, it will become evident that the experimental study of heredity, pursued on the lines Mendel has made possible, is second to no branch of science in the certainty and magnitude of the results it offers. This study has one advantage which no other line of scientific inquiry possesses, in that the special training necessary for such work is easily learnt in the practice of it, and can be learnt in no other way. All that is needed is the faithful resolve to scamp nothing.

If a tenth part of the labour and cost now devoted by leisured persons, in this country alone, to the collection and maintenance of species of animals and plants which have been collected a hundred times before, were applied to statistical experiments in heredity, the result in a few years would make a revolution not only in the industrial art of the breeder but in our views of heredity, species and variation. We have at last a brilliant method, and a solid basis from which to attack these problems, offering an opportunity to the pioneer such as occurs but seldom even in the history of modern science.

We have been told of late, more than once, that Biology must become an exact science. The same is my own fervent hope. But exactness is not always attainable by numerical precision: there have been students of Nature, untrained in statistical nicety, whose instinct for truth yet saved them from perverse inference, from slovenly argument, and from misuse of authorities, reiterated and grotesque.

The study of variation and heredity, in our ignorance of the causation of those phenomena, must be built of statistical data, as Mendel knew long ago; but, as he also perceived, the ground must be prepared by specific experiment. The phenomena of heredity and variation are specific, and give loose and deceptive answers to any but specific questions. That is where our exact science will begin. Otherwise we may one day see those huge foundations of “biometry” in ruins.

But Professor Weldon, by coincidence a vehement preacher of precision, in his haste to annul this first positive achievement of the precise method, dispenses for the moment even with those unpretending forms of precision which conventional naturalists have usefully practised. His essay is a strange symptom of our present state. The facts of variation and heredity are known to so few that anything passes for evidence; and if only a statement, or especially a conclusion, be negative, neither surprise nor suspicion are aroused. An author dealing in this fashion with subjects commonly studied, of which the literature is familiar and frequently verified, would meet with scant respect. The reader who has the patience to examine Professor Weldon’s array of objections will find that almost all are dispelled by no more elaborate process than a reference to the original records.

With sorrow I find such an article sent out to the world by a Journal bearing, in any association, the revered name of Francis Galton, or under the high sponsorship of Karl Pearson. I yield to no one in admiration of the genius of these men. Never can we sufficiently regret that those great intellects were not trained in the profession of the naturalist.

Mr Galton suggested that the new scientific firm should have a mathematician and a biologist as partners, and--soundest advice--a logician retained as consultant. Biologist surely must one partner be, but it will never do to have him sleeping. In many well-regulated occupations there are persons known as “knockers-up,” whose thankless task it is to rouse others from their slumber, and tell them work-time is come round again. That part I am venturing to play this morning, and if I have knocked a trifle loud, it is because there is need.

March, 1902.

Biometrika, I. Pt. I. p. 5.

CONTENTS.

INTRODUCTION.

THE PROBLEMS OF HEREDITY AND THEIR SOLUTION, pp. 1–39.

Preliminary statement of Mendel’s principles, 8. Relation of Mendel’s discovery to the law of Ancestral Heredity, 19. Heterozygote and Homozygote, 23. New conceptions necessitated by Mendel’s discovery, 26. Simple alternative characters, or allelomorphs, 27. Compound allelomorphs and their components, 29. Analytical Variations, 29. Relation of Mendel’s principle to continuous variation, 32. Dominance, 32. Non-Mendelian phenomena, 33. False hybrids of Millardet, 34. Brief historical notice, 36.

MENDEL’S EXPERIMENTS IN PLANT HYBRIDISATION, pp. 40–95.

Introductory Remarks, 40. Selection of Experimental Plants, 42. Division and Arrangement of Experiments, 44. Characters selected, 45. Number of first crosses, 47. Possible sources of error, 47. Forms of the Hybrids, 49. Dominant and recessive, 49.

First generation bred from the Hybrids, 51. Numbers of each form in offspring, 52. Second generation bred from the Hybrids, 55. Subsequent generations bred from the Hybrids, 57.

Offspring of Hybrids in which several differentiating characters are associated, 59. The reproductive cells of the Hybrids, 66. Statement of Mendel’s essential deductions, 67. Experiments to determine constitution of germ-cells, 68. Statement of purity of germ-cells, 72.

Experiments with Phaseolus, 76. Compound characters, 80. Concluding Remarks, 84.

MENDEL’S EXPERIMENTS WITH HIERACIUM, 96–103.

A DEFENCE OF MENDEL’S PRINCIPLES OF HEREDITY, 104–208.

Introductory, 104.

I. The Mendelian Principle of Purity of Germ-cells and the Laws of Heredity based on Ancestry, 108.

II. Mendel and the critic’s version of him.

The Law of Dominance, 117.

III. The facts in regard to Dominance of Characters in Peas, 119.

The normal characters: colours of cotyledons and seed-coats, 120. Shape, 122. Stability and variability, 124. Results of crossing in regard to seed-characters: normal and exceptional, 129. Analysis of exceptions, 132. The “mule” or heterozygote, 133.

IV. Professor Weldon’s collection of “Other evidence concerning Dominance in Peas.”