has been undertaken by Darwin in his selection
theory. Alfred Russell Wallace, who arrived at the same results
contemporaneously with and independently of Darwin, has, with praiseworthy
modesty, renounced his claim to priority of the discovery, as Darwin had
been longer engaged in working out his theories and had begun to collect
materials for proof.

* * * * * {38}

CHAPTER II.

HISTORY OF THE DARWINIAN THEORIES.

Sec. 1. _Darwin._

In order to explain the development of higher species from lower ones in a
natural way, Darwin starts from two facts. The first fact is, that all
individuals of the same species show, besides their specific similarity,
individual differences: a fact which we call the _law of individual
variability_. The other fact is, that each individual inclines to transmit
to his offspring all his qualities--not only the characteristics of the
species, but also those of the individual: a fact which we call the _law of
heredity_.

To show how the whole basis of explanation of the evolution of one species
from another is given in these two facts, Darwin calls attention to the
rules according to which the often extraordinarily great varieties of
domestic animals and cultivated plants are obtained and preserved; namely,
the rules of _artificial breeding_. The breeder simply selects from a
species those individuals having such individual qualities as he wishes to
preserve and to increase, and refrains from breeding those individuals
which do not possess the characteristics he wants or which possess them
only in a small degree. He continues the same process with the next
generation; and by the constant and effectual agency of the two {39}
before-mentioned laws, he will, after the lapse of a few generations, have
breeded a variety in which the characteristics originally belonging only to
a single individual have become common and permanent.

It is now important to consider whether nature, in _natural selection_
(whence the name "Selection Theory") does not act unconsciously according
to the same rules, and attain the same results, as man with his artificial
and intentional selection; and, furthermore, whether she does not reach
results which, according to that principle of natural selection, finally
explain the origin of all, even of the highest and most complicated
organisms, from one single original form or a few original and simplest
forms. Darwin finds these question