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.
