Ilango Arasiyal

Lamarck and Darwin theory use and disue law and the 2nd law of Lamarck
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Charles Darwin was an English naturalist who studied variation in plants and animals during a five-year voyage around the world. He explained his ideas on evolution in a book called On the Origin of Species, published in 1859.

The main features in his theory are that:

• individuals compete for limited resources
• individuals in a population show natural variation
• individuals with characteristics best suited to their environment are more likely to survive to reproduce
• 'successful' characteristics are inherited

Species unable to compete successfully eventually become extinct.

Darwin's ideas caused a lot of controversy, and this continues today. They can be seen as conflicting with religious views about the creation of the world and the creatures in it.

Lamarck's theory

Darwin was not the only person to develop a theory of evolution. Jean-Baptiste Lamarck was a French scientist who developed an alternative theory at the beginning of the 19th century. His theory centred on two ideas:

• the law of use and disuse
• the law of inheritance of acquired characteristics

His theory stipulated that a characteristic which is used more and more by an organism becomes bigger and stronger. One that is not used disappears eventually. Any characteristic of an organism that is improved through use is passed to its offspring.

These lists summarise the two different explanations for long necks in giraffe.

Lamarck

1. a giraffe stretches its neck to reach food high up
2. the giraffe's neck gets longer because it's used a lot
3. the giraffe's offspring inherit its long neck

Darwin

1. a giraffe with a longer neck can reach food high up
2. a giraffe is more likely to get enough food to survive to reproduce
3. a giraffe's offspring inherit its long neck

Lamarck's theory was eventually discredited because acquired characteristics do not have a genetic basis. In addition, his theory cannot account for all the observations made of life on Earth. For instance, it would predict that all organisms gradually become complex, and simple organisms disappear. Darwin's theory can account for the continued presence of simple organisms.

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In 1809, in his now famous Philosophie zoologique, Lamarck set out this idea more systematically in the form of two laws:

• First Law: In every animal that has not reached the end of its development, the more frequent and sustained use of any organ will strengthen this organ little by little, develop it, enlarge it, and give to it a power proportionate to the duration of its use; while the constant disuse of such an organ will insensibly weaken it, deteriorate it, progressively diminish its faculties, and finally cause it to disappear.
• Second Law: All that nature has caused individuals to gain or lose by the influence of the circumstances to which their race has been exposed for a long time, and, consequently, by the influence of a predominant use or constant disuse of an organ or part, is conserved through generation in the new individuals descending from them, provided that these acquired changes are common to the two sexes or to those which have produced these new individuals (Lamarck 1809, p. 235).