536 SCIENCE PROGRESS 



three points may be set down as well established : (i) The 

 variability of certain characters of the so-called Spanish variety 

 of the species Gallus bankwa, namely the comb in the male and 

 the beard in the female. (2) That this variability is largely 

 independent of the other characters of the variety. These appear 

 to have been little if at all affected by the modification of the 

 chosen characters. (3) That the variations can be accumulated 

 in the same direction through several successive generations. 

 The large number of persons engaged in the double series of 

 experiments places these results of their concurrent testimony 

 beyond doubt. Putting them together we may say that they 

 prove the independent and cumulable variability of two par- 

 ticular characters of a particular variety of a particular species. 

 If, however, these experiments are taken, as they must be, with 

 hundreds of other series of experiments undertaken by other 

 breeders by which they effected changes in other characters of 

 the same variety of fowl, it will be seen that similar truths have 

 been established in regard to a great number of them. And if 

 these experiments again are taken with the experiments of thou- 

 sands of other breeders of various varieties of the same species, 

 it will be seen that the evidence of the independent and cumulable 

 variability of at all events every conspicuous character of the 

 domestic fowl is immense. Lastly Gallus bankiva is not the only 

 species which has been modified by domestication into divergent 

 varieties. If with the foregoing facts we consider the great 

 number of animals and plants in regard to which similar truths 

 have been established by similar experiments, the total evidence 

 of independent and cumulable variability in the characters of 

 organic beings becomes enormous and affords the best possible 

 ground for the belief that the rule applies to every part of organic 

 nature as a whole. The best possible ; for what more can be 

 proved by any expressly devised experiments in the case of 

 species still undomesticated ? Only that the rule applies to yet 

 one more species or rather to one or more of its characters ; a 

 difference in the quantity of proof, not in its kind. Now to prove 

 the existence of such variability throughout organic nature is to 

 establish Darwin's law, at least as far as it can be established by 

 experimental proof. For that it is in fact only or chiefly by this 

 means that life as we now see it has been evolved, can be proved 

 if at all only by appeal to the geological record; it is matter of 

 inference from observation and not susceptible of experimental 



