184 NATURAL SCIENCE [September 
hypothesis enunciated, it remains to bring forward experimental 
evidence of the validity of the first part—ie., it is necessary to 
prove that in some cases more closely similar individuals Of a species 
show greater mutual fertility than less similar; in other words, that 
there may be a partial sterility between varieties. On this point 
Darwin has collected a considerable amount of evidence in his 
“Variation of Animals and Plants under Domestication.” A few 
of the cases mentioned there may be now cited. Thus Girtner 
found that a variety of dwarf maize, bearing yellow seed, showed a 
considerably diminished fertility with a tall maize having red seed, 
though both varieties were perfectly fertile when crossed inter se. 
Again, in the genus Verbascum, numerous experiments were made by 
Gartner with the white and yellow varieties of V. lychnitis and V. 
blattaria, he finding that crosses between similarly coloured flowers 
yielded more seed than those between dissimilarly coloured flowers. 
These experiments have been repeated and extended by Scott with 
confirmatory results. Again, Girou de Buzareingues crossed three 
varieties of the gourd, and concluded that their mutual fertilisation 
is less easy in proportion to the difference which they present. 
Still again, the blue and red varieties of pimpernel, which are con- 
sidered by most botanists as varieties, were found by Gartner to be 
quite sterile when crossed. 
With regard to members of the animal kingdom, there is very little 
evidence. Such as there is, is related only to domesticated animals, 
and can be at once objected to on the ground that it merely shows 
that the animals in question are descended from two or more dis- 
tinct species. Thus Youatt? states that longhorn and shorthorn 
cattle, when crossed, show a diminished fertility. This statement 
has, however, been denied by Wilkinson. 
The evidence determinable from certain anthropological data is, 
on the other hand, of more value. Thus Professor Broca has brought 
forward evidence * that some races of man show diminished fertility 
together. Again, according to statistics collected in Prussia from 
1875 to 1890, it was found that Protestants, Catholics and Jews, 
marrying among themselves, had, on an average, respectively 4°35, 
5°24 and 4°21 children. When, however, the husband was a Jew 
and the wife a Protestant or Catholic, the numbers of children were 
only 1°58 and 1°38 respectively ; and when the wife was a Jewess 
and the husband a Protestant or Catholic, only 1°78 and 1°66 re- 
spectively. Whether this apparent partial sterility was due to 
differences of race or to social reasons it was impossible to say.* 
Still again, from the natality tables of Korosi,> which are calculated 
1 2nd ed., vol. ii. p. 82. 2 ** Cattle,” p. 202. 
3 “On the Phenomena of Hybridity in the Genus Homo.” 1864. 
4 Quoted from Mayo Smith’s ‘‘ Statistics of Sociology,” p. 115. 
5 <¢ Phil; Trans.,” 1895, B..781. 
