xcli REPORT—1858. 
the variety of the species at an antecedent date and state of things will 
become the type-form of the species at a later date, and in an altered state 
of things. 
Mr. Charles Darwin had previously to Mr. Wallace illustrated this prin- 
ciple by ingenious suppositions, of which I select the following :—“ To give 
an imaginary example from changes in progress on an island:—let the 
organization of a canine animal which preyed chiefly on rabbits, but some- 
times on hares, become slightly plastic ; let these same changes cause the 
number of rabbits very slowly to decrease, and the number of hares to in- 
crease ; the effect of this would be that the fox or dog would be driven to 
try to catch more hares: his organization, however, being slightly plastic, 
those individuals with the lightest forms, longest limbs, and best eyesight, 
let the difference be ever so small, would be slightly favoured, and would 
tend to live longer, and to survive during that time of the year when food 
was scarcest; they would also rear more young, which would tend to 
inherit these slight peculiarities. The less fleet ones would be rigidly 
destroyed. I can see no more reason to doubt that these causes in a thou- 
sand generations would produce a marked effect, and adapt the form of the 
fox or dog to the catching of hares instead of rabbits, than that greyhounds 
can be improved by selection and careful breeding *.” 
Observation of animals in a state of nature is required to show their 
degree of plasticity, or the extent to which varieties do arise: whereby 
grounds may be had for judging of the probability of the elastic ligaments 
and joint-structures of a feline foot, for example, being superinduced upon 
the more simple structure of the toe with the non-retractile claw, according 
to the principle of a succession of varieties in time. 
Observation of fossil remains is also still needed to make known the ante- 
types, in which varieties, analogous to the observed ones in existing species, 
might have occurred, so as to give rise ultimately to such extreme forms as 
the Giraffe for examplet. 
This application of paleontology has always been felt by myself to be so 
important that I have never omitted a proper opportunity for impressing the 
results of observations showing the “ more generalized structures ” of extinct 
as compared with recent forms of mammalia. 
But, in pointing out how local changes might affect large quadrupeds, I 
* Proceedings of the Linnean Society, August 1858, p. 49. 
t “ The powerful retractile talons of the falcon- and the cat-tribes have not been produced 
or increased by the volition of those animals; but among the different varieties which oc- 
curred in the earlier and less organized forms of these groups, those always survived longest 
which had the greatest facilities for seizing their prey.’’—Wallace, p. 61. 
t “Neither did the giraffe acquire its long neck by desiring to reach the foliage of the 
more lofty shrubs, and constantly stretching its neck for the purpose ; but because any va- 
rieties which occurred among its antetypes with a longer neck than usual at once secured a 
Fresh range of pasture over the same ground as their shorter-necked companions, and on the 
first scarcity of food were thereby enabled to outlive them?’—Ib. p. 61. 
