LIFE: ITS ORIGIN AND NATURE S3 
from each parent; one quarter from each grand¬ 
parent; one eighth from each of its great-grand¬ 
parents—and so on forever backwards into the 
generations of the past. Each one of us, there¬ 
fore, represents a compound of all the gener¬ 
ations which have preceded us. We are, so to 
say, a composite photograph resulting from all 
of them. 
Very obviously, the body is thus subject to 
heredity; less obviously the mind. Prof. Ribot 
has, however, brought forward a mass of evi¬ 
dence, tending to show that mind is also sub¬ 
ject to this immutable law, in his work on 
“Heredity.” Environment and heredity are gen¬ 
erally conceded to be the two great factors 
which go to the moulding of any individual. 
Whether or not “acquired characteristics” are 
thus hereditary has been the subject of acute 
and prolonged controversy. Of late years, the 
tendency has been to disbelieve in such a pos¬ 
sibility, but recent researches have again given 
plausibility to this idea, and there is a tendency 
among certain biologists to swing in favor of 
this belief. 
How does heredity operate? It is now thought 
that there is a physical basis for heredity— 
this physical basis being the so-called “germ- 
plasm.” This germ-plasm is composed of germ 
cells, and in each cell is a nucleus. Within 
this nucleus are tiny thread-like bodies, known 
as “chromosomes.” These are the real carriers 
of heredity. There are a certain and definite 
number of these chromosomes (or idants), 
which vary in different animals and plants. 
These chromosomes, in turn, consist of “ids,” 
