, are
governed by one universal force of attraction. In like manner the
researches and investigations of the nineteenth century led to the
conviction that all forms of life upon the earth obey a universal law
of development. By this law the higher are evolved from the lower
through a succession of gradual but progressive changes.

This conception originated long before the beginning of the Victorian
era, but it lacked the support of carefully examined facts, and most
sensible men regarded it as nothing more than a plausible conjecture.
The thinker who did more than any other to supply the facts, and to
put the theory, so far as it relates to natural history, on a solid
and lasting foundation, was the distinguished English naturalist,
Charles Darwin.[1]

[1] Alfred Russel Wallace, also noted as a naturalist, worked out the
thoery of evolution by "natural selection" about the same time, though
not so fully, with respect to details, as Darwin; as each of these
investigators arrived at his conclusions independently of the other,
the theory was thus doubly confirmed.

On his return (1837) from a voyage of scientific discovery round the
world, Darwin began to examine and classify the facts which he had
collected, and continued to collect, relating to certain forms of
animal life. After twenty-two years of uninterrupted labor he
published a work in 1859, entitled "The Origin of Species," in which
he aimed to show that life generally owes its course of development ot
the struggle for existence and to "the survival of the fittest."

Darwin's work may truthfully be said to have wrought a revolution in
the study of nature as great as that accomplished by Newton in the
seventeenth century. Though it excited heated and prolonged
discussion, the Darwinian theory gradually made its way, and is now
generall received, though sometimes in a modified form, by practically
every eminent man of science throughout the world.

After Mr. Darwin began his researches, but before he completed them,
Sir William Grove, an eminent electrician, commenced a series of
experiments which resulted in his publishing his remarkable book[2] on
the connection of the physical forces of nature. He showed that heat,
light, and electricity are mutually convertible; that they must be
regarded as modes of motion; and, finally, that all force is
persistent and indestructible, thus proving, as Professor Tyndall
says, that "to nature, nothing can be added; f