The Struggle for Existence
The life of wild animals is a struggle for existence. The full exertion
of all their faculties and all their energies is required to preserve their
own existence and provide for that of their infant offspring. The possibility
of procuring food during the least favorable seasons and of escaping the
attacks of their most dangerous enemies are the primary conditions which
determine the existence both of individuals and of entire species.
The numbers that die annually must be immense; and as the individual
existence of each animal depends upon itself, those that die must be the
weakest -- the very young, the aged, and the diseased -- while those that
prolong their existence can only be the most perfect in health and vigor,
those who are best able to obtain food regularly and avoid their numerous
enemies. It is "a struggle for existence," in which the weakest and least
perfectly organized must always succumb.
Useful Variations Will Tend to Increase, Unuseful or Hurtful Variations to Diminish
Most or perhaps all the variations from the typical form of a species
must have some definite effect, however slight, on the habits or capacities
of the individuals. Even a change of color might, by rendering them more or
less distinguishable, affect their safety; a greater or less development of
hair might modify their habits. More important changes, such as an increase
in the power or dimensions of the limbs or any of the external organs, would
more or less affect their mode of procuring food or the range of country
which they could inhabit. It is also evident that most changes would affect,
either favorable or adversely, the powers of prolonging existence. An
antelope with shorter or weaker legs must necessarily suffer more from the
attacks of the feline carnivora; the passenger pigeon with less powerful wings
would sooner or later be affected in its powers of procuring a regular supply
of food; and in both cases the result must necessarily be a diminution of the
population of the modified species.
If, on the other hand, any species should produce a variety having slightly
increased powers of preserving existence, that variety must inevitably in time
acquire a superiority in numbers.
Lamarck's Hypothesis Very Different from that Now Advanced
The hypothesis of Lamarck -- that progressive changes in species have been
produced by the attempts of animals to increase the development of their own
organs and thus modify their structure and habits -- has been repeatedly and easily
refuted by all writers on the subject of varieties and species.
The giraffe did not acquire its long neck by desiring to reach the foliage
of the more lofty shrubs and constantly stretching its neck for the purpose,
but because any varieties which occurred among its ancestors with a longer
neck than usual at once secured a fresh range of pasture over the same ground
as their shorter-necked companions, and on the first scarcity of food were
thereby enabled to outlive them.
Journal of the Proceedings of the Linnean Society. August 1858, London