454 POPULAR SCIENCE MONTHLY 



matin. Professor Wilson has brought forward the convincing data 

 showing that the complex character of sex in insects actually resides 

 in or is determined by particular and definite masses of this wonderful 

 basis of inheritance. 



Mendel's principles also account in the most remarkable way for 

 many previously obscure phenomena, such as reversion, and again, the 

 case where a child resembles its grandparent more than either of its 

 parents; these seem to be due, so to speak, to the rise to the surface 

 of a hidden stream of germ-plasm that had flowed for one or many 

 generations beneath its accompanying currents. I believe that the law 

 is replacing more and more the laws of Galton and Pearson, formu- 

 lated as statistical summaries of certain phenomena of human inheri- 

 tance taken en masse. According to Galton's celebrated law of ances- 

 tral inheritance, the qualities of any organism are determined to the 

 extent of a certain fraction by its two parents taken together as a 

 mid-parent, that a smaller definite fraction is contributed by the grand- 

 parents taken together as a mid-grandparent, and so on to earlier 

 generations. But Mendel's Law has far greater definiteness, it explains 

 more accurately the cases of alternative inheritance, and it may be 

 shown to hold for blended and mosaic inheritance as well. 



De Vries's mutation theory has already been explained in an 

 earlier address by Professor Richards. It is clearly not an alternative 

 but a complementary theory to natural selection, the germ-plasm 

 and Mendelian theories. Like these last, it emphasizes the importance 

 of the congenital hereditary qualities contained in the germ-plasm, 

 though unlike the Darwinian doctrine it shows that sometimes new 

 forms may arise by sudden leaps and not necessarily by the slow and 

 gradual accumulation of slight modifications or fluctuations. The 

 mutants like any other variants must present themselves before the 

 jury of environmental circumstances, which passes judgment upon their 

 condition of adaptation, and they, too, must abide by the verdict that 

 means life or death. 



From what has been said of these post-Darwinian discoveries, the 

 Lamarckian doctrine, which teaches that acquired non-congenital char- 

 acters are transmitted, seems to be ruled out. I would not lead you to 

 believe that the matter is settled. I would say only that the non- 

 transmission of racial mutilations, negative breeding experiments upon 

 mutilated rats and mice, the results of further study of supposedly 

 transmitted immunity to poisons — that all these have led zoologists to 

 render the verdict of "not proved." The future may bring to light 

 positive evidence, and cases like Brown-Sequard's guinea-pigs, and 

 results like those of MacDougal with plants and of Tower with beetles 

 may lead us to alter the opinion stated. But as it stands now most 

 investigators hold that there are strong general grounds for disbelief 

 in the principle, and also that it lacks experimental proof. 



