As these travels,[10] undertaken at comparatively the same age, represent
the foundation upon which their scientific work and theories were based
during the long years which followed, a glance at the conditions
governing the separate expeditions--both mental and physical--may be of
some value. The most obvious difference lies, perhaps, in the fact that
Darwin was free from the thought of having to "pay his way" by the
immediate result of his efforts, and likewise from all care and anxiety
regarding domestic concerns; the latter being provided for him when on
board the _Beagle_, or arranged by those who accompanied him on his
travels overland and by river. The elimination of these minor cares
tended to leave his mind free and open to absorb and speculate at
comparative leisure upon all the strange phenomena which presented
themselves throughout the long voyage.

A further point of interest in determining the ultimate gain or loss
lies in the fact that Darwin's private excursions had to be somewhat
subservient to the movements of the _Beagle_ under the command of
Captain Fitz-Roy. This, in all probability, was beneficial to one of his
temperament--unaccustomed to be greatly restricted by outward
circumstances or conditions, though never flagrantly (or, perhaps,
consciously) going against them. The same applies in a measure to
Wallace, who, on more than one occasion, confessed his tendency to a
feeling of semi-idleness and dislike to any form of enforced physical
exertion; but as every detail, involving constant forethought and
arrangement, as well as the execution, devolved upon himself, the latent
powers of methodical perseverance, which never failed him, no matter
what difficulties barred his way, were called forth. Darwin's estimate
of the "habit of mind" forced upon himself during this period may not
inaptly be applied to both men: "Everything about which I thought or
read was made to bear directly on what I had seen, or was likely to see;