re 1859, when the
_Origin of Species_ was published.

Like Lamarck, Charles Darwin was, neither by inclination nor by
training, a morphologist. In his youth he was a collector, a sportsman
and a field geologist. His voyage round the world on the _Beagle_
aroused in him keen interest in the problem of species--their variety,
their variation according to place and time, their adaptedness to
environment. The conviction gradually took possession of his mind that
the puzzling facts of geographical range and geological succession which
he observed wherever he went were explicable only on the hypothesis that
species change. He was not satisfied with the theories of evolution that
had been proposed by his grandfather, by Lamarck, and by E. Geoffroy St
Hilaire--he did not indeed understand these theories any too well. He
resolved to work out the problem in his own way, for his own
satisfaction. He tells us all this very clearly in his autobiography.
"During the voyage of the _Beagle_ I had been deeply impressed by
discovering in the Pampean formation great fossil animals covered with
armour like that on the existing armadillos; secondly, by the manner in
which closely allied animals replace one another in proceeding
southwards over the continent; and thirdly, by the South American
character of most of the productions of the Galapagos archipelago, and
more especially by the manner in which they differ slightly on each
island of the group; some of the islands appearing to be very ancient in
a geological sense.

"It was evident that such facts as these, as well as many others, could
only be explained on the supposition that species gradually become
modified; and the subject haunted me. But it was equally evident that
neither the action of the surrounding conditions, nor the will of the
organisms (especially in the case of plants) could account for the
innumerable cases in which organisms of every kind are beautifully
adapted to their habits of life--for instance, a woodpecker or a
tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I
had always been much struck by such adaptations, and until these could
be explained it seemed to me almost useless to endeavour to prove by
indirect evidence that species have been modified."[351]

All Darwin's varied subsequent work revolved round these, for him,
essential problems--How do species change, and how do they become
adapted to their environment? He never ceased to be e