Answer :
Lamarck stressed two main themes in his biological work. The first
was that the environment gives rise to changes in animals. He cited
examples of blindness in moles, the presence of teeth in mammals and the
absence of teeth in birds as evidence of this principle. The second
principle was that life was structured in an orderly manner and that
many different parts of all bodies make it possible for the organic
movements of animals.[15]
Although he was not the first thinker to advocate organic evolution,
he was the first to develop a truly coherent evolutionary theory.[7] He outlined his theories regarding evolution first in his Floreal lecture of 1800, and then in three later published works:
Recherches sur l'organisation des corps vivants, 1802.Philosophie Zoologique, 1809.Histoire naturelle des animaux sans vertèbres, (in seven volumes, 1815–1822).Lamarck employed several mechanisms as drivers of evolution, drawn
from the common knowledge of his day and from his own belief in
chemistry pre-Lavoisier.
He used these mechanisms to explain the two forces he saw as comprising
evolution; a force driving animals from simple to complex forms, and a
force adapting animals to their local environments and differentiating
them from each other. He believed that these forces must be explained as
a necessary consequence of basic physical principles, favoring a
materialistic attitude toward biology.