July 28, 192 1] 



NATURE 



681 



book by a very distinguished biologist. He contro- 

 verted not a fact or an inference ; all he had to say 

 was : "The trail of the deductive thinker is over all." 

 But how on earth can any supp>osition be established 

 except by deduction? Crucial testing is deduction. 

 All interpretative science has been created by it. " If 

 my hypothesis be true and all others wrong, then this 

 thing, and that, and that other must be true also. 

 Let me see if it is so." Again, I once argued with 

 another distinguished biologist. "But isn't the evi- 

 dence true?" said I. "It may be," said he; "but 

 it's not the sort of evidence we accept nowadays!" 

 I found that his opinions corresponded with those of 

 the writer of the following passage, another very 

 distinguished biologist : — 



"The recognition that only by experimental methods 

 can we hope to place the study of zoology on a footing 

 with the sciences of chemistry and physics is a com- 

 paratively new conception, and one that is by no 

 means admitted as yet by all zoologists. I do not 

 wish to disparage those studies that deal with the 

 descriptive and the historfcal problems of biology. 

 ... It is undoubtedly true that many zoologists who 

 have spent their lives in acquiring a broad know- 

 ledge of the facts of their science fail to make use 

 of their information by testing the very problems that 

 their work suggests. This ^s owing, no doubt, to 

 their exclusive interest in the observational and de- 

 scriptive sides of biology, but also in part, I think, to 

 the fact that the experimental method has not been 

 recognised by zoologists as the most important tool 

 that scientists employ . . . the essence of the experi- 

 mental method consists in requiring that every sug- 

 gestion (or hypothesis) be put to the test of experi- 

 ment before it is admitted to a scientific status. From 

 this point of view the value of a hypothesis is to be 

 judged, not by its plausibility, but bv whether it 

 meets the test of experiment. ... It is sometimes 

 said that Nature has already carried out innumerable 

 and wonderful experiments. . . . Let us not be blinded 

 by rhetorical questions of this kind." And so on, and 

 so forth. 



I wonder if anyone can tell us of a passage in 

 any sort of literature which contains more misunder- 

 standing than the one I have quoted. "Rhetorical " 

 indeed ! Oj course, the essence of the experimental 

 method is not that every suggestion shall be put to 

 the test of experiment. Experiment is a mode of 

 observing, not of thinking. It is used only when the 

 desired facts cannot be directly observed, and only 

 for the purpose of removing the conditions which 

 obscure them. O/ course, physics and chemistry are 

 advanced and accurate, not because of difficulties in 

 observing, but only because their workers have veri- 

 fied both their facts and their thinking, because they 

 have accepted all tested suppositions readily, and be- 

 cause they have been in a position to measure and 

 weigh accurately. They are experimental only be- 

 cause, from the nature of things, most of the desired 

 facts were obscured and could not be revealed except 

 by some device. Physicists and chemists would not 

 be so silly as to experiment if they could observe at 

 sight. As a fact, nearly all their established truths 

 started with suppositions founded on patent facts, and 

 were tested experimentally only because of the paucity 

 of such evidence. There is nothing sacrosanct about a 

 fact discovered experimentally, or about a hypothesis 

 so tested. If you twist a dog's tail experimentally, 

 the howl you elicit is not in the least more valuable 

 intrinsically than the tail which you observe directly. 

 You prove a man a thief just as surely by observing 

 the spoons sticking out of his pockets as by turning 

 them out. O/ course, experiment is valuable ; but we 



NO. 2700, VOL. 107] 



need not assign it wrong values. It enables us to pene- 

 trate below the surface. But a diving dress is not the 

 only wear. There are things worth knowing on the sur- 

 face — so many things, nearly all the facts of zoology, 

 botany, and most other biological sciences, that if 

 they be ignored, crucial testing is impossible. O/ 

 course, hypotheses, founded on or even confirmed by 

 experiment, are, like all other untested hypotheses, 

 mere guesses; whereas all tested hypotheses, whether 

 proved experimentally or otherwise, are in a differeni 

 category : for a real test is crucial ; it not only con- 

 firms the truth, but also eliminates the untruth. If 

 literature be examined I think it will be found that 

 when anyone insists that all suppositions must be put 

 to the test of experiment, he really asks that we shall 

 ignore all evidence except that revealed by experi- 

 ment, and all suppositions except those founded on 

 experiment — that, in fact, wei shall grant his facts 

 the same status and his opinions the same immunity 

 from criticism that other sectarians {e.g. Mohamme- 

 dans) claim for their evidence and opinions. Com- 

 pare Newton, who when he found that the moon's 

 orbit (a thing which must be directly observed) did 

 not, as then calculated, fit into his theory of gravita- 

 tion, laid aside his supposition for many years, and 

 published it only when a fresh inquiry demonstrated an 

 error in the first calculation. Consider the glaring 

 truism that "Variation is the sole cause of non-in- 

 heritance ; apart from variations, like exactly begets 

 like when parent and offspring develop under like 

 conditions." No biologist will venture to dispute that 

 truism. Is it necessary to test it experimentally? If 

 it be true, what becomes of the Lamarckian and Neo- 

 Darwinian suppositions, and much besides that bio- 

 logists have unendingly "tested" experimentally and 

 unendingly disputed about ? 



When such freakish, partisan stuff as I have quoted 

 can be published and applauded, is it not evident that 

 biology must remain a tumbling ground for whimsies 

 unless its workers discuss and agree on its rules of 

 procedure? The rules under which other interpreta- 

 tive sciences have been created — that language must 

 be precise and significant, that all verifiable facts are 

 equal before science, that all suppositions must be 

 crucially tested before admittance to a scientific status, 

 and that all fully tested suppositions must be candidly 

 accepted— are so few and simple that were they 

 rigorously applied, then, since the evidence is so abun- 

 dant, it is certain that biology would soon rank among 

 the greatest, best estabHshed, and most useful of 

 sciences. It is generally thought that the multiplicity 

 and diversity of biological phenomena, derived» as they 

 are, or should be, from so many sciences, make the 

 task of the inquirer peculiarly difficult. Actually the 

 reverse is the case; for, when evidence is abundant 

 and diverse, opportunities for testing are correspond- 

 ingly frequent and established truth, rightly sought, 

 should soon cover a wide area. Other sciences halt 

 while evidence is painfully collected ; biology halts be- 

 cause the methods of its students are such that they 

 are unable to use the abundant evidence already avail- 

 able. 



Dr. Bather says d propos of recapitulation : " At the 

 moment when his letter was published some of us 

 werei discussing that very question at the Linnean 

 Society, and Sir Archdall Reid, had he been present, 

 would have seen that the issue was far from being 

 the simple one that he imagines." As readers of 

 Nature know, I am very modest and retiring. Never- 

 theless, if Dr. Bather will indicate his difficulties I 

 believe I can help him. The truth is, I have, on 

 one hand, great faith in ordinary scientific procedure, 

 and on the other, amid vast ignorance, a knowledge 



