Lamarck’s theory of evolution

His theory involves the inheritance of acquired characters. The theory is resolved into three components: • Influence of the environment • Use and disuse of body parts • Inheritance of acquired characters Individuals of the same species growing and developing under different environmental conditions differ from one another. Etiolation occurs in plants grown in darkness. Amphibious plants are heterophyllous. Plants therefore react to external environment changes and it is possible that cumulative effects, produced by the changed conditions through successive generations, might give rise to new species. In animals, the use or exercise of certain parts of the body results in development of those parts. New characters are thus acquired in life and it is possible that these may be passed on to the offspring, giving rise to new species. Take evolution of the giraffe from its shortnecked ancestors. In the arid interior of Africa, where the giraffe lived and fed on leaves of trees, it might have needed to stretch its neck and limbs to reach the leaves of taller trees, a process which gradually lengthened the neck and fore-limbs. If these new characters could have been passed on to the offspring over generations, the modern long-necked giraffe might have resulted. Similarly, parts which are not used or exercised might degenerate and disappear or persist as vestiges. The appendix in people is believed to have been comparative to the caecum of rodents in a time when people were herbivores. When people changed from the herbivores mode of feeding to the omnivores type, the caecum was no longer used in digestion. It therefore degenerated into a vestigial structure, the appendix. A character was therefore acquired through disuse, and passed on the offspring. Lamarck’s theory helped prepare the way for the acceptance of evolution, but his views were never widely accepted. Although changes do take place in the body of an organism during its lifetime, no one has been able to prove that these changes are inherited. This means that the genotype is not changed by characteristics acquired during the life-time of an organism. Since Lamarck’s time, countless experiments performed y biologists have failed to confirm his theory.