1878.] Doctrine of Development. 455 
elimination of the slower and the preservation of the swifter 
forms. 
From butterflies we pass to birds. In a work containing 
much with which we are unable to agree,* the author, con- 
tending that over-preserving and the extirpation of hawks 
have not led to the multiplication of weak and sickly grouse, 
which formerly would have been improved away, and have 
left more scope for their stronger and healthier fellows, 
argues that it is not the weaker and slower birds which fall 
victims to the falcon. The celerity of this destroyer is so 
tremendously in excess of that of the fleetest grouse that 
all differences in speed among the latter birds utterly vanish. 
The strongest-winged and most vigorous moorcock, if once 
espied in the air by the enemy, has practically no greater 
chance of escape than a feeble and sickly bird. On the 
contrary, the boldest and most energetic grouse, who may 
fairly be assumed to be, as a rule, the healthiest, will fall 
victims more frequently than their weaker brethren, from 
the mere fact that they are more active and venturesome, 
and hence more likely to be on the wing. The effects ot 
the co-existence of falcons and grouse in any country will 
be, therefore, not the development of a form of the latter 
better adapted for rapid flight, and ultimately, in the course 
of many generations, endowed with longer and more pointed 
wings, but merely a thinning of numbers, which will tell 
equally upon the strong and the weak, and which in some 
cases may even give an advantage to the latter. 
This argument of Mr. Morant’s concerning the influence 
of the falcon upon the development of the grouse appears 
to us applicable not merely to this individual instance, but 
to every case where a bird or a beast has to struggle for 
existence against enemies greatly its superiors in speed, in 
strength, or in general resources. Slight increments of 
swiftness or force, trifling improvements in offensive or de- 
fensive arms, would be absolutely thrown away under such 
circumstances, however valuable they might be as against 
an enemy but slightly superior to the original form. Hence 
there are numbers of cases where it must become question- 
able how, on the principle of Natural Selection, advances 
in these important directions are to be effected. If variation 
proceeds not at one uniform rate and by gradations almost 
imperceptible, but occasionally by more rapid movements, 
the matter is entirely different. Nor are considerations of 
* “ Game-Preservers and Bird-Preservers.” See Quarterly Journal of 
Science, vii., 145. 
