August 24, 1906.] 



SCIENCE. 



227 



Evolution of Man' and 'Principles of 

 Heredity,' shown a new path for investi- 

 gators to follow. 



The attempt to resuscitate Lamarck's 

 views on the inheritance of acquired- char- 

 acters has been met not only by the demand 

 for the production of experimental proof 

 that such inheritance takes place, which 

 has never been produced, but on Weis- 

 mann's part by a demonstration that the 

 reproductive cells of organisms are devel- 

 oped and set aside from the rest of the 

 tissues at so early a period that it is ex- 

 tremely improbable that changes brought 

 about in those other tissues by unaccus- 

 tomed incident forces can be communicated 

 to the germ-cells so as to make their ap- 

 pearance in the offspring by heredity. 

 Apart from this, I have drawn attention to 

 the fact that Lamarck's first and second 

 laws (as he terms them) of heredity are 

 contradictory the one of the other, and 

 therefore may be dismissed. In 1894 I 

 wrote : 



Normal conditions of environment have for 

 many thousands of generations moulded the in- 

 dividuals of a given species of organism, and de- 

 termined as each individual developed and grew 

 ' responsive ' quantities in its parts ( characters ) ; 

 yet, as Lamarck tells us, and as we know, there 

 is in every individual born a potentiality which 

 has not been extinguished. Change the normal 

 conditions of the species in the case of a young 

 individual taken to-day from the site where for 

 thousands of generations its ancestors have re- 

 sponded in a perfectly defined way to the normal 

 and defined conditions of environment; reduce the 

 daily or the seasonal amount of solar radiation 

 to which the individual is exposed; or remove the 

 aqueous vapor from the atmosphere; or alter the 

 chemical composition of the pabulum accessible; 

 or force the individual to previously unaccustomed 

 muscular effort or to new pressures and strains; 

 and ( as Lamarck bids us observe ) , in spite of all 

 the long-continued response to the earlier normal 

 specific conditions, the innate congenital po- 



- 1 use the term ' acquired ' without prejudice 

 j.n the sense given to that word by Lamarck him- 

 self. 



tentiality shows itself. The individual under 

 the new quantities of environing agencies shows 

 new responsive quantities in those parts of its 

 structure concerned, new or acquired characters. 



So far, so good. What Lamarck next asks us 

 to accept, as his ' second law,' seems not only to 

 lack the support of experimental proof, but to be 

 inconsistent with what has just preceded it. The 

 new character which is ex hypothesi, as was the 

 old character (length, breadth, weight of a part) 

 which it has replaced — a response to environment, 

 a particular moulding or manipulation by incident 

 forces of the potential congenital quality of the 

 race — is, according to Lamarck, all of a sudden 

 raised to extraordinary powers. The new or freshly 

 acquired character is declared by Lamarck and 

 his adherents to be capable of transmission by 

 generation; that is to say, it alters the potential 

 character of the species. It is no longer a merely 

 responsive or reactive character, determined 

 quantitatively by quantitative conditions of the 

 environment, but becomes fixed and incorporated 

 in the potential of the race, so as to persist when 

 other quantitative external conditions are substi- 

 tuted for those which originally determined it. 

 In opposition to Lamarck, one must urge, in the 

 first place, that this thing has never been shown 

 experimentally to occur; and in the second place, 

 that there is no ground for holding its occurrence 

 to be probable, but, on the contrary, strong reason 

 for holding it to be improbable. Since the old 

 character (length, breadth, weight) had not be- 

 come fixed and congenital after many thousands 

 of successive generations of individuals had de- 

 veloped it in response to environment, but gave 

 place to a new character when new conditions 

 operated on an individual (Lamarck's first law), 

 why should we suppose that the new character 

 is likely to become fixed after a much shortet 

 time of responsive existence, or to escape the opera- 

 tion of the first law? Clearly there is no reason 

 (so far as Lamarck's statement goes) for any 

 such supposition, and the two so-called laws of 

 Lamarck are at variance with one another. 



In its most condensed form my argument 

 has been stated thus by Professor Poulton : 

 Lamarck's "first law assumes that a past 

 history of indefinite duration is powerless 

 to create a bias by which the present can 

 be controlled; while the second assumes 

 that the brief history of the present can 

 readily raise a bias to control the future" 

 {Nature, Vol. LI., 1894, p. 127). 



