A paper was here read by O. F. Cook, Botanist in charge of Tropical Agriculture, 

 U. S. Department of Agriculture: 



EVOLUTION UNDER DOMESTICATION 



[This paper has not been submitted for publication, but the discussion thereon is given below.] 



W. Bateson: The author of this paper raises a number of questions ol very great 

 theoretical importance. As I understand it, he proposes to distinguish variations accord- 

 ing as they are debilitating, or, if I understand rightly, progressive. Such distinctions 

 have, of course, in the past been attempted, but I feel that we should be better able to 

 appreciate his position if he would indicate the tests by which he proposes to draw those 

 distinctions. For my own part, I know no such tests, and I should like to ask him how 

 he would propose to apply a test that would distinguish the debilitating variation from 

 the pi^ogressive variation. 



O. F. Cook: I am not trying to do what has been done in the past in that direction, 

 but recognize the debilitation of a symptom of an evolutionary debility, if you will allow 

 that expression (I don't know of one that will meet the case any better), and that those 

 variftions called mutations and also variations from many hybrids where the fertilization 

 fails to grow, or is incomplete, are symptoms of organic or evolutionary debility. The 

 test is not in the variation itself so much as in the history, as these things may be learned 

 from our knowledge of the history of plants. On the other hand, there is, I think, prob- 

 ably a difference in the variations as noted; that is, there are (i) these abrupt variations 

 without the gradations, and (2) the multitude of intergradations that we find in large 

 species in nature which are freely breeding. We get these pronounced variations, which, I 

 believe, are abnormal, and although there is no distinction to be drawn perhaps between 

 the kinds of variation, there is a difference, as we might say, in the temperature 

 of the body. We find a man l^ing on the street or somewhere; we find virnether he is 

 warm or not, and if he is cold we think he is dead. If he is warm we think he is alive; 

 if he is extremelv warm we recognize that he is ill. And so I think with this variation. 

 It is a quality that is normal to a certain degree and may be abnormal in a greater 

 degree. 



W. Bateson: I want to know how we are able to recognize these differences. The 

 speaker tells us that he will distinguish certain variations in a certain way, but I want 

 to know how we can do it. What we want is a thermometer. 



O. F. Cook: This, of course, is a question of degree. I think it is a matter that 

 needs to be used with some sympathy, perhaps, to be appreciated. But I cited the coffee 

 as a typical instance of a plant which, without selection, was producing relatively sterile 

 varisticns. I may say also that I found excellent opportunities in Guatemala recently to 

 see the tests of the varieties that have been advertised in coffee, and also to see a great 

 many of these mutations that are exceedingly interesting, but much less fertile than the 

 parent. The infertility occurs with offspring that produce a small number of berries, or 

 that produce an abnormal number of berries, with but a small number of seeds, and so 

 on through, and all these in the aggregate are less fertile than the parent form. Now, 1 

 am associating that fact with the historical fact of inbreeding, unintentional in this case, 

 and associating it also with the general well-known fact that close breeding 

 tends to sterility. That is a fact that I do not pretend to explain in the sense of a 

 molecular or other cause. I am simply suggesting that association, and that associatio-.i 

 applies not only in the cases where it has been applied, but to a much larger extent than 

 has been supposed. In the case of the wheat there is a distinction to be drawn. We 



