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LAMARCKIANEVOLUTION

© 2008 Paul Billiet ODWS 

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 Jean Baptiste LAMARCK  1744 – 1829  Lamarck rejected

fixity

He proposed a theoryof evolution which isattractive but it waseventually rejectedbecause of the wayinheritance works

Lamarck 

© 2008 Paul Billiet ODWS 

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 Adaptation and specialisation

Lamarck noticed that organisms adaptedto a particular niche had well developedspecialised organs

For example a carnivore will have longcanine teeth to grip its prey

© 2008 Paul Billiet ODWS 

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 vestigial organs

Small non-functional organs (vestigialorgans)

e.g. the appendix in humans, the internal

hind limbs of whales and the internal legsof some species of snakes

Comparative anatomy showed that theseorgans resembled those which were muchmore developed, with particular functions,in other species

© 2008 Paul Billiet ODWS 

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 The Law of Use and Disuse

He proposed that if an organ is used a lotit 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 

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 The Inheritance of Acquired

Characteristics  if an organism developed a characteristic feature

through adapting to a new way of life during itslifetime, it would pass this on to its offspring

The classic example given is that of the giraffe’sneck

As the giraffe’s ancestors searched for a richerfood supply they stretched to reach higherbranches in trees

Thus their stretched bodies were passed ontotheir offspring

© 2008 Paul Billiet ODWS 

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Lamarck v Darwin

Lamarck’s theory required adaptation to createnew variations

This was followed by the inheritance of thesecharacteristics

Darwin’s theory requires random hereditaryvariation first, followed by selection of thevariations

The argument was over when Mendel’s laws of genetics were rediscovered at the end of the 19thcentury

Variations are due to hereditary traits passingfrom one generation to the next in predictablefrequencies

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Disproving Lamarck 

Characteristics acquired during the lifetime of aparent are not passed onto the offspring

An athlete who develops a large muscle massthrough training does not have children whoalready possess this large muscle mass

Ernst HaeckelIn an attempt to disprove Lamarckism he is saidto have cut off the tails of mice for severalgenerations

The babies born from this line of tailless mice stillgrew tails as long as their ancestors

This was not exactly a fair test as the mice hadnot stopped using their tails in an attempt toadapt to their environment

They still found their tails useful

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Lamarckism in evolution theory

today  Behaviour can be different

Some behaviour patterns are innate and will alsoevolve 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 theselearned skills onto others including their children

This pattern of evolution resembles theLamarckian pattern

The evolution of learnt behaviour is much fasterthan genetic evolution and it plays an importantrole in human cultural evolution