CHROMOSOME THEORY OF HEREDITY 245 



Emerson as having proclaimed, " I accept the Universe. . . ." 

 (" Gad ! She'd better ! " was the sage's comment !) 



But the real conflict is between the upholders of chance 

 variation and those who believe in the direct action (not in- 

 direct, as in Natural Selection), of the environment ; or in an 

 hereditary effect of the organism's own efforts, own functioning. 



There can be no doubt but that the gene idea is at present 

 the merest approximation to reality ; if it is true, the labours 

 of analysing a unit-complex consisting of several thousand 

 units, each of these composed of one or many molecules of 

 hundreds or more probably thousands of atoms each, will be 

 prodigious. But, if it is any approximation at all to reality, 

 then nine-tenths of any and every Lamarckian theory falls to 

 the ground. Professor MacBride refers to the " factor-mad 

 pupils of Professor Morgan." But, with such a conception 

 opening up before them, a conception of a material unit of 

 exact composition, but of a complexity undreamt-of even in 

 organic chemistry, a mechanism which resists change sufficiently 

 to allow hundreds of thousands of separate species to co-exist 

 upon this globe, preserving their incredible diversity often in 

 spite of similarity of outer environment — perhaps a little 

 enthusiasm, leading to statements which may appear exag- 

 gerated, but have not been proved untrue, is pardonable — 

 pardonable especially when it is the outcome of the most 

 laborious experimental research, and not of speculations which 

 for the present appear to be often unverifiable. 



There remains the other essential side of heredity : the 

 translation of the constitution, in certain conditions of environ- 

 ment, into the adult organism, 



A formal possibility of such development has already been 

 set forth in the writings of His, Roux, Jenkinson,^ and others. 

 Briefly, if we have a constitution of some complexity, together 

 with any localisation of material or of structure within the 

 germ, whether pre-existent or caused by outer stimulus, we 

 can theoretically understand the production of a gradually 

 increasing complexity in the developing organism. 



It will help us if we take a more tangible example. We 

 have already considered the origin of the two types of gross 

 differentiation to be seen in fertilised ova, the localisation of 

 organ-forming substances, and the pre-existence of a polarity 

 or gradient. If, as we postulate, the constitution proper is 

 lodged in the chromosomes, both pre-localisation of substances 

 and polarity being in the long run determined by the environ- 

 ment in relation with the constitution, we shall have the same 

 chromosomal constitution in each and all of the cells into which 



1 See Jenkinson, Experimental Embryology, Oxford, 1909, which contains 

 references to earlier work^ 



