The change in the heritable traits of a population over successive generations, as determined by shifts in the allele frequencies of genes is called evolution. All contemporary organisms are related to each other through common descent. It is products of cumulative evolutionary changes over billions of years. Evolution is the source of the vast diversity of extant and ex:net life on Earth. Different theories of evolution were put forwLrd. The theory of natural selection is most acceptable Merv).
THEORY OF ACQUIRED CHARACTERS
Jean Baptiste Lamarck ( 7-14—I829) as a French zoologist. he studied animal classification. Ile gave a theory how change occurs. I le believed that species are not constant. 1 herelore. the existing species were derived from preexisting species.
Theory of inheritance of acquired characteristics
Lamarck explained the mechanism of evolutionary changes. De proposed the theory of inheritance of acquired characteristics. Lamarck believed that organisms develop new organs or modify existing organs due to environmental problems. Thus the organs changes according to need. Lamarck used the example of the giraffe. he described that the ancestral giraffes had short necks like other mammals. It strains his neck to reach higher branches during browsing. Thus it acquired higher shoulder and longer necks. These modifications were passed on to the next generation. The use of any organ make it highly developed. The disuse of an organ causes degeneration. Therefore, it can describe the evolution of highly specialized structures like vertebrate eyes.
Criticism and objections on the theory of Lamarck
Lamarck published his theory in 1802. he had to face the social and scientific criticism. Society was not accepting his ideas of evolutionary changes. He did not have much evidence to support it.
So this theory would not convince most scientists. Thus, Lamarck
was much criticized for ideas of evolutionary change at that time. Today. he is criti ized for his mechanism of inheritance and evolutionary chang . This mechanism lack reasonable evidences. The changes are passed to the next generation by gametes. For example, change in neck of giraffe does not occur in genetic material. So it cannot be transferred to the next generation.