22Section I.G. Sergi. 
are abstract objections, and are not based upon observed or observable 
facts, and because they are the effect of theories upon the origins of the 
forms which have never been verified by facts. 
As regards the external tegumentary characters with their adjuncts, the 
colour of the skin, of the hair, and of the iris, and the characters of the 
hair and of the eyes, we can affirm categorically that to-day these are as 
fixed as the skeletal characters. Their formation and their origin elude 
modern investigations but must be as primordial as the formation of the 
human varieties under various influences, especially geographical and local, 
and of immemorial time. These characters now resist all other influence 
different from that which has contributed to produce them, and hence do 
not exhibit variations, but on the contrary preserve a fixed heredity. 
Only in crossings) the external characters undergo alterations, as is easily 
proved in mulattos by the union of negroes with whites or other varieties of 
colour. Studies, researches, inquiries have been made to determine if the 
characters which, after aid, are derived from many factors behave according 
to the Mendelian heredity, or do not follow it. In this field we have the 
labours of Mendelians, such as Bateson, Davenport, Hurst, and the labours 
of the Biometricians, such as Pearson and others, the one class in opposition 
to the other. But the same supporters of the Mendelian heredity, such as 
Bateson and Doncaster, admit the necessity for new and rigorous observa­ 
tions in order to be able to prove decisively that human heredity proceeds 
according to Mendel’s theory—for there are still opposing facts which 
depend on many factors and various conditions—in order to be able to decide 
about the hereditary nature of them in the same way as is done in the 
case of many animals and many plants. Taking one’s stand, however, on 
the general theory, if Mendelian heredity is constantly verified in the animal 
kingdom, there should be no reason why it should not be found to apply 
in man. As to this question, Doncaster believes he can write that “ In this 
respect crosses between different races of mankind resemble hybrids between 
different species of animals and plants, except that there is usually no 
sterility.” He is not accurate in one respect, the crossing in the human 
race not being fertile indefinitely as is commonly believed. For the rest, 
that Mendelian heredity is found only in the crossing of varieties and 
cannot take place in the crossing of species, cannot at present be absolutely 
affirmed. Experiments exist of plants which tend to show Mendelian 
heredity also in the crossing of species, and Bateson awaits experiments for 
a safe affirmation in one or the other sense. So, also, as regards crossing 
in man, we are in the same expectant attitude. 
In any case the fact of heredity in disease and in deformities of human 
organs is established, as may be read in the works of many writers who treat 
particularly of the subject. Whether this heredity assumes the Mendelian 
form, complete or incomplete, is an inquiry which does not much concern us 
here, inasmuch as it has an exclusively theoretical character and value.