from pole to pole, one hundred layers deep. But there is no
such danger. Year by year the mulleins hold their own and no more. Any
particular field may have more or less, but in the long run the
average for a district is about the same. Some of the seeds are poor
and thin. These scarcely sprout. Others spring up into thin-skinned
plants, and the first frost nips them. Still others lack the woolly
coating in its finest abundance, and the browsing animals eat these.
Others lack power to put out a wide-ranging root supply and the first
drought kills these. Still others fail to send up a vigorous stem and
the passing animal knocks them over and they die. Of the few that are
still surviving, some produce such small and inconspicuous blossoms
that the insects scarcely see them, and they go unfertilized. In the
end only the aristocrats of the group are left, aristocrats in the
best sense of the word. These are strong, thrifty, and beautiful, and
are provided with every defense known to the mullein world. From these
the mulleins of the next generation will spring. Again Nature will
select the best of these, by a repetition of the same process. Thus
year by year the stock is improved. Any new feature that is favorable
helps its possessor to survive, and, if happily mated, will show
itself after a while in the entire group. This, in brief, is the
underlying idea of Natural Selection, as Darwin conceived it.

In 1842, at Lyell's suggestion, Darwin wrote a short sketch of his
ideas which he, two years later, expanded into a somewhat larger
account. The manuscript of these early views of the theory was
completely lost and has only been recovered within the last few years.
It was recently published under the editorship of Charles Darwin's
son, Francis. It is astonishing to see how clearly the first short
sketch states the underlying conception which all of Darwin's
subsequent work amplifies. Hooker was constantly urging Darwin to
write out his whole theory in the form of a book, and Darwin had begun
to do so in 1856.

Meanwhile, down in the Moluccas, Alfred Russell Wallace had been lying
sick of a fever contracted during his exploring expedition in that
neighborhood. He had been studying the distribution of the animal life
of the Malay Archipelago. Overcome by sickness, as he lay in bed, he
began to think over a book which he had read not long before, "Malthus
on Population." Wallace had been pondering on the question of the
origin