it again. In addition it
gained him the esteem of a new circle of scientists and that a
decidedly exclusive circle.

The publication of these books did much for Darwin. His narrative of
the voyage gained the good will of cultured England in general. The
book on coral reefs won the geologists. His "Manual of the
Cirrhipedia" (as the barnacle book was called) secured the attention
of systematic zooelogists. The time was not far distant when he would
need every aid possible toward gaining and keeping the regard of men;
for he was to promulgate a theory that would arouse the bitterest
opposition and the keenest scorn.

All the while Darwin was working on these books his mind was quietly
busying itself with what he called the species question. The more he
studied the material collected on his long tour, the more confident he
became that the animals of the present are the altered descendants of
the animals of the past. He tried patiently to work out every
conceivable hypothesis to see whether he could account for the
alteration. He felt quite sure animals changed, but how they changed,
and why, he could not for a long time conceive. He knew that gardeners
were constantly producing new varieties of plants, and that animals of
various breeds were clearly the descendants of other and familiar
varieties. Accordingly he began to study the methods of animal and
plant breeders, to visit their farms, to open correspondence with them
and read all their trade journals, to undertake experiments in the
breeding of plants. The longer he worked the more confident he became
of the reality of the change; but for a long time no glimmer of the
cause by which it could be brought about came to his mind. In 1838 he
came across a book by Malthus called "An Essay on Population," in
which the author shows that, whereas man increases by a geometric
ratio, he cannot hope to increase his food supply in more than an
arithmetic ratio. That is, while the food might increase like the
series 2-4-6-8-10, the population would increase like the series
2-4-8-16-32. On this basis it is only a question of time when the
earth will be too full of people for it to be possible for the food to
sustain them. Malthus added many observations and suggestions, but
this is as much of the book as interests us in this connection. Here
was the idea that suggested to Darwin his agency for producing the
change of the animals of the past into those of the present.

The numbe