LAMARCKIAN EVOLUTION © 2008 Paul Billiet ODWSODWS

Jean Baptiste LAMARCK 1744 – 1829  Lamarck rejected fixity  He proposed a theory of evolution which is attractive but it was eventually rejected because of the way inheritance works Lamarck © 2008 Paul Billiet ODWSODWS

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 ODWSODWS

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 ODWSODWS

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 ODWSODWS

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 ODWSODWS

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

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 Haeckel In 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

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