nce. It is his nature, not
his nurture, that is mainly responsible for his character.

CHAPTER II

MODIFICATION OF THE GERM-PLASM

Every living creature was at some stage of its life nothing more than a
single cell. It is generally known that human beings result from the
union of an egg-cell and a sperm-cell, but it is not so universally
understood that these germ-cells are part of a continuous stream of
germ-plasm which has been in existence ever since the appearance of life
on the globe, and which is destined to continue in existence as long as
life remains on the globe.

The corollaries of this fact are of great importance. Some of them will
be considered in this chapter.

Early investigators tended naturally to look on the germ-cells as a
product of the body. Being supposedly products of the body, it was
natural to think that they would in some measure reproduce the character
of the body which created them; and Darwin elaborated an ingenious
hypothesis to explain how the various characters could be represented in
the germ-cell. The idea held by him, in common with most other thinkers
of his period, is still held more or less unconsciously by those who
have not given particular attention to the subject. Generation is
conceived as a direct chain: the body produces the germ-cell which
produces another body which in turn produces another germ-cell, and so
on.

But a generation ago this idea fell under suspicion. August Weismann,
professor of zooelogy in the University of Freiburg, Germany, made
himself the champion of the new idea, about 1885, and developed it so
effectively that it is now a part of the creed of nearly every
biologist.

Weismann caused a general abandonment of the idea that the germ-cell is
produced by the body in each generation, and popularized the conception
of the germ-cell as a product of a stream of undifferentiated
germ-plasm, not only continuous but (potentially at least) immortal.
The body does not produce the germ-cells, he pointed out; instead, the
germ-cells produce the body.

The basis of this theory can best be understood by a brief consideration
of the reproduction of very simple organisms.

"Death is the end of life," is the belief of many other persons than the
Lotus Eaters. It is commonly supposed that everything which lives must
eventually die. But study of a one-celled animal, an Infusorian, for
example, reveals that when it reaches a certain age it pinches in two