LAMARCK THEORY OF EVOLUTION

Jean Baptiste Lamarck (1744–1829) was a distinguished French zoologist.
His contributions to zoology include important studies of animal
classification. Lamarck, however, is remembered more for a theory
of how change occurs. He believed that species are not constant
and that existing species were derived from preexisting species.
Lamarck’s rather elaborate explanation for evolutionary
change involved a theory that was widely accepted in the early
1800s called the theory of inheritance of acquired characteristics.
Lamarck believed that organisms develop new organs or modify existing
organs as environmental problems present themselves. In
other words, organs change as the need arises. Lamarck illustrated
this point with the often-quoted example of the giraffe. He contended
that ancestral giraffes had short necks, much like those of any
other mammal. Straining to reach higher branches during browsing
resulted in their acquiring higher shoulders and longer necks. These
modifications, produced in one generation, were passed on to the
next generation. Lamarck went on to state that the use of any organ
resulted in that organ becoming highly developed and that disuse resulted
in degeneration. Thus, the evolution of highly specialized
structures, such as vertebrate eyes, could be explained.
Lamarck published his theory in 1802 and defended it in the
face of social and scientific criticism. Society in general was
unaccepting of the ideas of evolutionary change, and evidence for
evolution had not been developed thoroughly enough to convince
most scientists. Thus, Lamarck was criticized in his day more for advocating
ideas of evolutionary change than for the mechanism he
proposed for that change. Today, he is criticized for defending a mechanism
of inheritance and evolutionary change that is now known to
lack reasonable supporting evidence. For a change to be passed on to
the next generation, it must be carried by gametes. Changes in the giraffes’
necks, as envisioned by Lamarck, could not be passed on because
they did not originate as changes in the genetic material. Even
though Lamarck’s mechanism of change was incorrect, he should be
remembered for his steadfastness in promoting the idea of evolutionary
change and for his other accomplishments in zoology.