EVOLUTION AND MENDELISM 221 



that of the disciples of Mendel, who by cross breeding closely 

 allied varieties of animals and plants have shown how parental 

 characters are rearranged in the descendants. The Mendelians 

 have undoubtedly thrown more light on the nature of heredity 

 than all the earlier investigators together, and the facts they 

 have revealed are of the utmost importance not only to the 

 horticulturist and the stock breeder, but in showing how it 

 may be possible to eliminate certain defects, and foster desirable 

 qualities in the human species. 



In his addresses as President of the British Association at 

 Melbourne and Sydney in 1914, Prof. Bateson reviewed some 

 of the more striking results obtained by the Mendelians, and 

 the bearing of the discoveries on human progress. The 

 Melbourne address was devoted mainly to the relations of 

 Mendelian facts to evolutionary theories, and many of the 

 statements made are so startling and so opposed to views 

 that have been very largely held in the past that one feels 

 somewhat bewildered. 



As is well known, the Mendelians, by cross breeding two 

 varieties of a species which differ in regard to a certain character 

 which is being studied, find that though the character may not 

 be manifest in the resulting offspring it reappears in a certain 

 proportion of the next generation ; and further that a definite 

 proportion of this last generation breed true as regards the 

 characters of the original parents experimented on. From 

 this it is assumed that the characters of any plant or animal 

 are due to certain genetic factors which are present in the 

 germ cells, and that if the form could reproduce itself 

 asexually or if the two sexes were perfectly similar as regards 

 their genetic factors, each generation would be like the 

 previous one. 



It is accepted as an " essential principle, that an organism 

 cannot pass on to offspring a factor which it did not itself 

 receive in fertilisation," and also that " parents which are 

 both destitute of a given factor can only produce offspring 

 equally destitute of it." How then, it may be asked, can new 

 forms arise ? On this point there does not seem to be complete 

 agreement among Mendelians. Lotsy believes that all new 

 forms are the result of crossing, and even goes the length of 

 suggesting that the first vertebrate arose from the crossing 

 of two invertebrates. Bateson, while he does not disguise his 

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