LAMARCKIAN EVOLUTION

1. LAMARCKIAN EVOLUTION © 2008 Paul Billiet ODWS

2. Lamarck Jean Baptiste LAMARCK1744 – 1829 • Lamarck rejected fixity • He proposed a theory of evolution which is attractive but it was eventually rejected because of the way inheritance works © 2008 Paul Billiet ODWS

3. Adaptation and specialisation • Lamarck noticed that organisms adapted to a particular niche had well developed specialised organs • For example a carnivore will have long canine teeth to grip its prey © 2008 Paul Billiet ODWS

4. vestigial organs • Small non-functional organs (vestigial organs) • e.g. the appendix in humans, the internal hind limbs of whales and the internal legs of some species of snakes • Comparative anatomy showed that these organs resembled those which were much more developed, with particular functions, in other species © 2008 Paul Billiet ODWS

5. The Law of Use and Disuse • He proposed that if an organ is used a lot it will develop and strengthen • If it is not used it will atrophy • He called this the law of use and disuse © 2008 Paul Billiet ODWS

6. The Inheritance of Acquired Characteristics • if an organism developed a characteristic feature through adapting to a new way of life during its lifetime, it would pass this on to its offspring • The classic example given is that of the giraffe’s neck • As the giraffe’s ancestors searched for a richer food supply they stretched to reach higher branches in trees • Thus their stretched bodies were passed onto their offspring © 2008 Paul Billiet ODWS

7. Lamarck v Darwin • Lamarck’s theory required adaptation to create new variations • This was followed by the inheritance of these characteristics • Darwin’s theory requires random hereditary variation first, followed by selection of the variations • The argument was over when Mendel’s laws of genetics were rediscovered at the end of the 19th century • Variations are due to hereditary traits passing from one generation to the next in predictable frequencies

8. Disproving Lamarck • Characteristics acquired during the lifetime of a parent are not passed onto the offspring • An athlete who develops a large muscle mass through training does not have children who already possess this large muscle mass • Ernst HaeckelIn an attempt to disprove Lamarckism he is said to have cut off the tails of mice for several generations • The babies born from this line of tailless mice still grew tails as long as their ancestors • This was not exactly a fair test as the mice had not stopped using their tails in an attempt to adapt to their environment • They still found their tails useful

9. Lamarckism in evolution theory today • Behaviour can be different • Some behaviour patterns are innate and will also evolve in by natural selection • learned behaviour patterns can be changed within a generation • Members of a social group who have acquired the behaviour in their lifetimes will pass these learned skills onto others including their children • This pattern of evolution resembles the Lamarckian pattern • The evolution of learnt behaviour is much faster than genetic evolution and it plays an important role in human cultural evolution