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Lamarck - an alternative
theory of evolution
Jean-Baptiste Pierre Antoine de Monet,
Chevalier de Lamarck
Charles Darwin was not the first person to propose that species can change
over time into new species—that life, as we would say now, evolves. In 1801,
more than 50 years before Darwin published his theory of evolution, JeanBaptiste Lamarck proposed his own theory.
Lamarck realised that over time environments can change and therefore, he
argued, organisms must change their behaviour in order to survive. If
organisms began to use a particular organ more than they had in the past,
then that organ would increase in size or importance during the lifetime of
the organism. For example, Lamarck thought that if a giraffe stretched its
neck more to get food then over the course of its lifetime, the giraffe’s
neck would grow longer. This characteristic would then be passed onto the
Giraffe’s offspring who would inherit the longer neck. Continued stretching
would make the neck grow longer still over several generations. He also
thought that the opposite was true - organs that organisms stopped using
would shrink.
Lamarck also did not believe in extinction. He believed that nature caused
simple organisms to continuously evolve into more complex forms. Therefore,
he thought, species never become extinct; they just evolved into a more
complex version of organism.
Charles Darwin – evolution by
natural selection
Charles Robert Darwin
1809 - 1882
In 1859 Darwin published his now famous book 'On the Origin of Species by
Means of Natural Selection'. At the time it was both ground-breaking and
Darwin was heavily influenced by the theory that the fossils found in rocks
were actually evidence of animals that had lived many thousands or millions
of years ago. During an expedition to the Galapagos Islands, 500 miles west
of South America, Darwin noticed that each island supported its own form
of finch which were closely related but differed in important ways.
Darwin proposed a theory of evolution occurring by the process of natural
selection. The organisms best adapted to their environment are more likely
to survive and reproduce, passing on the characteristics which helped them
survive to their offspring. Those members of the population less suited to
the environment do not survive or reproduce. In this way, a species changes
to become adapted to its environment gradually over a long period of time.
This theory is often referred to as ‘survival of the fittest’.
Darwin believed that if organisms could not adapt quickly enough to changes
in their habitat, or were faced with competition from a better adapted
species, that their numbers would reduce and that they could eventually
become extinct.