THEORIES OF EVOLUTION
Lamarck's 'theory of inhertitance' was further studied by a group of scientists. Their ideas supporting Lamarck's opinion collectively constitute neo-Lamarckism.
The neo-Lamarckians were of the opinion that 'adaptions' are universal in nature. An adaptation happens through causal relationship of structure, function and environment. Due to changes in the environment, habits and life style of organism gets altered. Thus gradually the organism acquires new structures. The newly obtained character gradually becomes an inheritable trait. This opinion and argument is a modified form of Lamarckism. These ideas stressed direct action of environment on organisms.
Support to neo-Lamarckian concept - Experiments
1. McDougall (1938) tried to prove that learning is an acquired character that can be inherited. He did his experiments on rats.
He deviced a 'T' shaped tank. The tank had two exits. One exit was well lighted. However at the terminal region of the exit he deviced an arrangement for giving electrical shock. The pathway to the other exit was kept dark. At the terminal exit point a small piece of cheese was kept as a reward. McDougall dropped several rats into the tank. Many of the rats preferred lighted pathway to escape and at the exit they received electric shock. Those rats, that preferred dark pathway received the cheese. He repeated the trial several times. Gradually many rats learnt the correct route for escape. Subsequently the rats were allowed to breed and the next generation developed.
The same experiment was repeated in the second generation. According to Mc Dougall, it was claimed that the number of mistakes committed, gradually got reduced. The speed of learning increased from generation to generation. Thus he concluded that learning is an acquired character.
However later workers found some technical mistakes in the work of Mc Dougall. The same experiment while repeated in other laboratories failed to give similar results.
2. Temperature related changes in the body of mice was noted by F.B.Sumner (1910). He reared one set of white mice in warmer temperature (20 - 300c) and another set in cold conditions. He found that in warmer conditions the mice developed larger ears and longer tails. He further claimed that these characters were inherited.
Through similar works claim for inheritance of acquired characters were made by Lindsey, Guyer and Smith and Kammerer. In all these works while repeating, critics have found technical mistakes and rejected them outright.
However, the controversy over 'inheritance' of acquired characters still continues. This theory of Lamarck while has not been disproved totally, it remains to be proved correct.