Mutations and Evolution. 
215 
selection. It seems reasonable to suggest that the so-called death- 
feigning instinct in many insects probably originated in the same 
way. So far as I know, this is the first suggestion of a mutation 
in an instinct. It would be selected in those insects in which such 
action would save their lives. 
The hornless condition in cattle is another mutation of much 
interest. Horns are known from the palaeontological record to 
have undergone a gradual progressive development in various 
groups of Mammals, while in the polled breeds the horns have 
apparently been suddenly lost through a mutation. Punnett 1 has 
suggested that the hornless condition may have co-existed in a 
species along with the gradual development of horns. Since the 
polled condition is dominant, however, at least in cattle, the 
recessives would all be devoid of a factor for hornlessness. 
And since the horns are a highly serviceable and necessary weapon 
of defence in the wild species, it seems very probable that the 
original hornless type would be stamped out by selection as soon as 
horns developed far enough to become a valuable weapon. This 
would take place whatever the causes of the progressive develop¬ 
ment of horns. There are no traces of hornless cattle before the 
historic era, although Herodotus describes the domestic cattle of 
the Scythians as hornless. In the last two centuries many hornless 
varieties have arisen and the origin of some polled breeds is known. 2 
The hornless mutation is in a sense a reversion as regards that 
character, and as such is comparable with peloria in flowers. The 
polled Hereford breed originated from a mutant at Atkinson, 
Kansas in 1889. 3 Being dominant, it cannot be supposed to have 
been present in the germplasm before its external appearance. 
An interesting and little known work by Bonavia (1895), while 
containing some unacceptable ideas, devotes a chapter to 
monstrosities as probable factors in the creation of species. 
Among fishes are cited the sword-fish Histophorus gladius with its 
upper jaw prolonged, Hemiramphius and various others with the 
lower jaw prolonged; also Zygoena the hammer-headed shark, 
which may have originated monstrously by a projection of both ocular 
regions. A hairless condition is normal in certain races of Chinese 
and Mexican dogs. It occurs as an anomaly in horses cattle and 
dogs, and hairlessness in man “ may have occurred all of a sudden 
1 Mendelism. MacMillan. 
1 See MacDonald and Sinclair, 1882. History of polled Angus cattle, 
8 Walter, H. E. Genetics, MacMillan, 1913, 
