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Powerpoint Presentation: Lamark

 

Evolution Index

The origins of life
Evolution and Fixity
Natural selection
Antibiotic Resistance
Industrial melanism
Palaeontology : The study of fossils
The C-14 Decay Curve
In Search of Deep Time
Evolution of the Horse
Punctuated Equilibrium
The classification of living organisms : Taxonomy
Kingdoms
Humans: Neotonous, bipedal African apes
The Hominids
The Changing Trees of Human Evolution
Genetic verses Cultural Evolution
Phenylketonuria (PKU) Fact Sheet
Cystic Fibrocis (CF) Fact Sheet

Topic Chapters Index

 

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 (as Jacques Monod put "Chance and necessity").

The argument was over when Mendel's laws of genetics were rediscovered at the end of the 19th century. He showed that variations are due to hereditary traits passing from one generation to the next in predicable frequencies.

 

EVOLUTION

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Lamarkian Evolution

Jean Baptiste 1744 - 1829 French botanist

Jean-Baptiste de Monet Chevalier de Lamarck

Jean-Baptiste de Monet Chevalier de Lamarck (1744-1829)
by Charles Thévenin (Public Domain image)

Unlike many of his contemporaries Lamarck rejected fixity. He proposed a theory of evolution which is attractive but it was eventually rejected because of the way inheritance works.

 

The Law of Use and Disuse

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.

More important he noticed that some organisms possessed 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. Through comparative anatomy it could be seen that these organs resembled those which were much more developed, with particular functions, in other species.

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.

 

The Inheritance of Acquired Characteristics

Lamarck's theory for the mechanism of evolution was based upon the idea that 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.

 

Disproving Lamarck

From observing the patterns of inheritance in families it can be seen that 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.

One famous evolutionist and supporter of Darwin was 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

Though the physical and biochemical features of an organism are inherited and evolve by natural selection, behaviour can be different. Some behaviour patterns are innate and will also evolve in by natural selection but 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

 

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