LAMARCKIAN EVOLUTION

© 2008 Paul Billiet ODWS

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 ODWS

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

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

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

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

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 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

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