928 



SCIENCE. 



[N. S. Vol. XI. No. 285. 



isms are isolated from one another either 

 geographically or in consequence of their 

 habits. There are probably many causes 

 which prevent conjugation, but, whatever 

 they may be, the efifect of them is to break 

 up organisms into specific groups, the 

 gametes of which do normally conjugate 

 with one another. 



In many cases, no doubt, the gametes of 

 organisms which are kept apart in Nature 

 by mechanical barriers will conjugate fully 

 if brought together. But in the great ma- 

 jority of cases it is probable that no amount 

 of proximity will bring about complete con- 

 jugation . There is physical incompatibility. 

 Here is a fruitful opening for investigation. 

 Observations are urgently needed as to the 

 real nature of this incompatibility. 



IMPOETANCE OF THE STUDY OF VARIATION. 



Another and most important effect of 

 conjugation is, as we have seen, the much- 

 spoken-of constitutional or genetic varia- 

 tions. They are, as we have already in- 

 sisted, of the utmost importance to the 

 evolutionist. Evolution would have been 

 impossible without them, for it is made up 

 of their summation. It becomes, there- 

 fore, desirable to find out to what extent a 

 species is capable of varying. This can 

 only be done, as Mr. Bateson has pointed 

 out, by recording all variations found. Mr. 

 Bateson, in his work already referred to, 

 has carried this out, and has shown the 

 way to a collection of these most important 

 data. In order to carry it further, I would 

 suggest that the collection be made not only 

 for structure, but also for function. This 

 has been done largely for the nervous func- 

 tions by psychologists and naturalists who 

 pay special attention to the instincts of 

 animals ; but we want a similar collection 

 for other functions. For instance, the vari- 

 ations in the phenomena of heat and men- 

 struation, and of rut amongst mammals, 

 and so on. To do this is really only to 



apply the methods of comparative anatomy 

 and comparative physiology to the mem- 

 bers of a species, as they have already been 

 applied to the different species and larger 

 groups of the animal kingdom. Such in- 

 vestigations cannot fail to be of the greatest 

 interest. Indeed, when we have learnt the 

 normal habits and structure of a species, 

 what more interesting study can there be 

 than the study of the possibilities of varia- 

 tion contained within it ? Then when we 

 know the limits of variability of any given 

 specific group, we proceed to try if we can 

 by selective breeding or alteration of the 

 conditions of life alter the variability, and 

 perhaps call into existence a kind of varia- 

 tion quite different in character from that 

 previously obtained as characteristic of the 

 species. 



THE EVOLUTION OF HEREDITY AND THE 

 ORIGIN OF VARIATION. 



These remarks bring me to the consider- 

 ation of a point to which I am anxious to 

 call your attention, and which is an im- 

 portant aspect of our subject. Has the 

 variability of organisms ever been different 

 from what it is now ? Has or has not evo- 

 lution had its influence upon the property 

 of organisms as it is supposed to have had 

 upon their other properties ? There is only 

 one possible answer to this question. Un- 

 doubtedly the variability of organisms must 

 have altered with the progress of evolution. 

 It would be absurd to suppose that organ- 

 isms have remained constant in this respect 

 while they have undergone alteration in all 

 their other properties. If the variability of 

 organisms has altered, it becomes necessary 

 to inquire in what direction has it altered ? 

 Has the alteration been one of diminution, 

 or has it been one of increase ? Of course, 

 it is possible that there has been no general 

 alteration in extent with the course of evo- 

 lution, and that the alteration, on the 

 whole, has been one of quality only. But 



