The theory of organic evolution seems to be the most acceptable explanation of the occurrence of varied forms of plants and animals on Earth. Evolution, which started out as a hypothesis, is now supported by evidence from many fields of science. The various convincing evidences for the occurrence of descent with modification is summarised in the Fig. 15. 1. Evidence [...]
Jean Baptiste Lamarck put forth the theory of inheritance of acquired characters, which is also known as Lamarckism. It was published in 'Philosophie Zoologique' in the year 1809. The four propositions of Lamarckism are as follows: a. Living organisms and their parts tend to increase in size continuously due to internal forces of life. b. New organs are formed in [...]
A reproductive isolating mechanism is a structural, functional, or behavioural characteristic that prevents successful reproduction from occurring between different species. This helps in accumulating genetic variations in species. If reproductive isolation does not exist, variant forms freely interbreed with the normal forms and this would lead to intermixing of their genotypes. These mechanisms are of two types: 1. Pre-Mating Mechanisms: [...]