



LOTSY, CURRENT THEORIES OF EVOLUTION. 397 
cultures we have come across such cases, but have not ventured 
to exploit them, since wild type flies are always present in the 
laboratory and hence the discovered form may have arisen through 
contamination. Thus even when a red eyed vellow fly appeared 
in the white-eyed yellow stock, there is the barest chance that a 
yellow red-eyed fly or an egg of such a fly had somehow gotten 
into the stock.” 
This is admirably sincere, but justifies my position that positive 
proof of the existence of mutation has not yet been obtained. But 
even supposing, for argument’s sake, that MORGAN's aberrant forms 
were mutants, then still they would have no evolutionary value, 
as MORGAN himself says that he does not consider them large 
enough to transgress the limit of the group of individuals known 
to taxonomists as Drosophila ampelophila or, more recently, as 
D. melanogaster. 
As a matter of fact different eyecolors, differences in hoariness 
and other such minor differences, or defects such as crumpled or 
abortive wings are all diversities observed within every Linnean 
species and to them any particular value in evolution, can hardly 
be ascribed. Whenever they appear, nature — Drosophila itself 
shows it — very soon succeeds in eliminating most of them. 
In this respect MorGANn’s mutants differ considerably from those 
of DE VRIES; the latter obtained aberrant forms which did trans- 
gress the limits of Oenothera Lamarckiana, so that I cannot escape 
the feeling, that while the hunt of dame variability started with 
the pursuit of big game, it has gradually dwindled to that of game 
decreasing perpetually in size, so that, while gone out to hunt 
elephants, some of us now express satisfaction at the death of a 
mouse! The reason for this, it seems to me, is the continuation of 
the belief that the diversity which we observe in nature, can be 
explained in one way only, to wit on the assumption of the existence 
of some kind of transmittable variability. Still it has long been 
known, that diversity, can be caused in another way, to wit by: 
Hybridisation. 
But this effect of hybridisation has, for a long time, been explained 
away by assuming that the diversity observed after hybridization, 
