446 / ARTHUR THOMSON [june 



fact — that there have been many consummate naturalists who never 

 asked the fourth question at all, who took nature as they found it, saw 

 it, saw its activity, saw its " whence," but never inquired as to its 

 " how " ! To omit this question now would be to label oneself a Rip 

 Van Winkle ; not to have asked it in pre-Darwinian days, or to have 

 refused its legitimacy as a scientific question was quite congruent 

 with the intellectual environment of the time. But Darwin gave 

 naturalists a new organon, not to use which means " an unlit lamp and 

 an ungirt loin." 



On the other hand, it is equally evident that in our attempt to 

 answer the question " How has this come to be as it is ? " we must 

 keep in touch with the actual facts of the case. We may take advan- 

 tage of intricate mathematical methods in our study of variation, but 

 we must be continually returning to the actual cabbages in the garden 

 and the real herrings in the sea. AVe may take advantage of logical 

 controversies about natural selection to sharpen our intellectual weapons, 

 but we must be continually returning to an actual observation and 

 measurement of the struggle for existence among the crabs on the shore 

 or among the seedlings in the plot. We may use abstract hypotheses, 

 such as Weismann's theory of the germ-plasm — which even its fiercest 

 critics must admit to be one of the most logically ingenious and com- 

 plete hypotheses in the history of science, and to have provoked re- 

 search more than any other biological idea except that of natural 

 selection — but as Weismann says — " the test of the usefulness of 

 theories lies in the applying them to special phenomena ; it then be- 

 comes apparent whether and where they touch improbabilities, and 

 where new facts are required to improve them or to replace them by 

 others." We may think out our hypotheses by the fireside, but this 

 will be of little avail unless we condescend to test them in open air. 



Even in regard to experiment, while there is no lack at present 

 of ingenuity in playing tricks with cells and eggs, embryos and larvae, 

 and while no one can predict the outcome of what Darwin called fools' 

 experiments, it is plain that those are likely to be of most value which 

 are definitely related to the possibilities of actual occurrence in 

 nature. 



It must be clearly understood that the evolutionist has not at 

 present any rounded-off and demonstrated generalisations like the law 

 of the conservation of energy or the law of gravitation. He has a 

 certain way of looking at things, he believes that they have had a 

 natural history, he has a formula, a modal interpretation, the general 

 idea of evolution. He has also particular causal theories, all of them 

 very young, which he seeks to test, but which from the nature of the 

 case he has little hope of demonstrating in the strict sense. With 

 his general idea and his particular causal theories, his continual occu- 

 pation is to see whether his keys fit the locks of actual fact — an 

 occupation of perennial interest. Sometimes he has fancied himself 



