Consideration of Weismann’s Arguments 199 
on grass and herbs would force some of these animals 
to feed on tree leaves, others to become transformed into 
rodents and insectivors or to undergo some transforma- 
tion of still another kind. 
In this connection it is to be especially noted that 
just because a large number of the individuals of the 
old species will thus have come to seek their nourish- 
ment elsewhere, no change will appear in those remaining 
behind in the former conditions of nourishment. In 
other words the elimination caused by the change in 
their habits of the overcrowding individuals from among 
the company of the old species will leave the other 
individuals of this species, whose number will now be 
no longer too great, in the same conditions of environ- 
ment as formerly, without any overcrowding and con- 
sequently there will not be any further causes provoking 
in these individuals also a transformation into another 
species. 
The change of nutrition will induce then a whole 
series of changes in the functions of seeking food, hunt- 
ing, fighting, seizing, chewing etc., but only for that 
position of the species which has changed its mode of 
living. Thus it is clear how, during a series of entire 
geological periods, a certain number of the ancestors 
of individual species that are now quite different from 
them were able to preserve themselves unaltered and 
so to reproduce their descendants unaltered to this day. 
Man is distinguished from other animals perhaps in 
this, that whereas the latter do not modify their environ- 
ment or modify it only indirectly and intermittently by 
emigration or by overcrowding and consequently make 
no progress in their development so long as their environ- 
ment undergoes no alteration from one of the causes 
