666 REPORT— 1901. 



Section D— ZOOLOGY. 

 Pbi5sit)T)Nt ov the Sectiox, — Professor J. COSSAR EWAHT, ]\[.D,, F.K.S, 



THURSDAY, SEPTEMBER 2. 

 The President delivered the following Address : 



Tlie Experimental Study of Vcoriation. 



The study of variation may be said to consist (1) in noting and classifying tlie 

 differences between parents and their offspring; and (2) in determining by obser- 

 vation and experiment the causes of these differences, especially wliy only some of 

 them are transmitted to future generations. The facts of variation having been 

 dealt with at considerable length in a recent work by Mr. Bateson, I shall discuss 

 chiefly the causes of variation. 



Though for untold ages parents have doulitless observed differences in the form 

 and temperament of their children, and though breeders have long noted unlooked- 

 for traits in their flocks and herds, the systematic study of variation is of very 

 recent date. This is not surprising, for, while the belief in the immutability of 

 species prevailed, there was no special incentive either to collect the facts or 

 inquire into the causes of variation ; and since the appearance in 1859 of the 

 ' Origiii of Species,' biologists have been mainly occupied in discussing the theory 

 of natural selection. Now that discussions as to the nature and origin of species no 

 longer occupy the chief attention of biologists, variability— the fountain and origin 

 of progi'essive development — is likely to receive an ever-increasing amount of notice. 

 Strange as it may appear, naturalists at the end of the eighteenth century con- 

 cerned themselves more with the causes of variation than their successors at the 

 end of the nineteenth. Buffon, who discus.sed at some length nearly all the 

 great problems that interest naturalists to-day, after considering variation arrived 

 at the conclusion that it was due to the direct action of the environment, and 

 even invented a theory (strangely like Darwin's theory of pangenesis), to explain 

 how somatic were converted into germinal variations. Erasmus Darwin and 

 Lamarck also had views as to the causes of variation. Erasmus Darwin believed 

 ■variability resulted from the efforts of the individual, new structures being 

 gradually evolved by organisms constantly endeavouring to adapt themselves 

 to their surroundings. Lamarck about the same time endeavoured to jjrove that 

 changes in the environment produced new needs, which in turn led to the forma- 

 tion of new organs and the modification of old ones, use being especially potent in 

 perfecting the new, disuse in suppressing the old. Both Erasmus Darwin and 

 Lamarck, without attempting, or apparently even seeing the need of, any sucli 

 explanation as pangenesis otlered, assumed that definite acquired modifications 

 were transmitted to the offspring, and they both further assumed that variations 

 occurred not in many but in a single definite direction ; hence they had no need 

 to postulate selection. The speculations of Erasmus Darwin and Lamarck having 



