[From the Proceedings of the American Association for the 

 Advancement of Science, Vol. xlvi, 1897.] 



Modification and variation and the limits of organic selkction. 

 By Prof. Henry F. Osborn, Columbia University, New Yorlc and 

 Prof. Edward B. Poulton, Oxford University, England. 

 (Abstract of Professor Osborn's paper.) 



Organic selection is the term proposed by Prof. Mark Baldwin and 

 adopted by Prof. C. Lloyd Morgan and the author, for a process in nature 

 which is believed to be atrue cause of definite or determinate evolution in 

 certain stuctures. The hypothesis is briefly as follows : that ontogenetic 

 adaptation is a very profound character. It enables animals and plants to 

 survive very critical changes in their environment. Thus all the individ- 

 uals of a race are similarly modiflc d over such long periods of time that 

 very gradually congenital or phylogenetic variations which happen to 

 coincide with the ontogenetic adaptive variations, are selected. 'I'hus 

 there would result an apparent, but not real transmission of acquired 

 characters. 



This hypothesis, if it has no limitations, brings about a very unexpected 

 harmony between the Laniarckian and Darwinian aspects of evolution, 

 by mutual concessions upon the part of the adherents of both theories. 

 While it abandons the transmission of acquired characters, it plnces indi- 

 vidual adaptation first, and fortuitous variation second, as Lamarckians 

 have always contended, instead of placing survival conditioned by fortu- 

 itous variations first and foremost, as selectionists have contended. 



This hypothesis has been endorsed by Alfred Wallace It appears to 

 the author, however, that it is subject to limitations, and exceptions which 

 go far to nullify its universal application. This is especially seen in the 

 fact that the law of Determinate Variation is observed to operate with 

 equal force in certain structures, such as the teeth, which are not im- 

 proved by individual use or exercise, as strongly as in structures which are 

 so improved. A very large class of determinate variations in other 

 stationary characters, such as the inner parts of the .-kull, also remain 

 unexplained. The author's studies of teeth in a great many piiyla of 

 Mammalia in past time liave convinced him that there are fundamental 

 predispositions to vary in certain directions ; that the evolution of the 

 teeth is marked out beforehand by hereditary influences which extend 

 back hundreds of thousands of years. These predispositions are aroused 

 under certain exciting causes and the progress of teeth development takes 

 a certain form converting iuto actuality what has hitherto been poteulial- 

 ity. 



This paper was discussed by Dr. Theodore Gill and Prof. Edward D 

 Campbell. 



(Abstract of Professor Poulton's paper.) 

 It must be admitted that the adaptation of the individual to its en- 

 vironment during its own lifetime possesses all the significance attributed 

 to It by Professor Osborn, Professor Baldwin, and Professor Lloyd Mor- 



(23!)) 



