1) Theory of need- the production of a new organ or part of a plant or animal results from a need

2) Theory of use and disuse- organs remain active as long as they are being used but disappear gradually with disuse

3) Theory of inheritance- all that has been acquired or changed in the structure of individuals during their life is transmitted by heredity to the next generation.

He believed evolution took place over a very long period of time.

Lamarck also divided animal life into the categories of vertebrates and invertebrates.

The contributions of Lamarck are worth considering, not because he successfully accounted for the process of evolution, since his ideas have never been supported by evidence, but because he at least provided a plausible theory for the multiplicity of forms of living things. His work attempted to change how people of the time thought about themselves and their origins by challenging the popular belief in creationism.

Lamarck's real contribution to scien

Morgan's findings in relation to the fruit fly were crucial to his most important idea: the chromosomal theory of heredity. He proposed that each chromosome contains a collection of small units called genes, with different genes having specific locations along specific chromosomes.

The study of specimens from his voyage on the ship The Beagle, that took Darwin to such places as Australia, South America, and the Galapagos Islands, convinced him that modern species evolved from earlier ones. Darwin also found many instances of striking similarities across a wide variety of organisms, such as the same basic limb structure in humans, bats and whales.

Much was learnt from Morgan's work on the fruit fly. It was his method as much as his results that contributed to major advances in scientific understanding as well as changing the nature of scientific thinking. Morgan and his team are credited with the changing the field of biology to a science based upon a rigorous experimental method. His results also provided the scientific world with many new theories of inheritance, which expanded upon the theories of Mendel.

2) The frequency of crossing-over between alleles of two different genes is proportional to distance between them on the chromosome

Mendel's laws remain, in essence, untouched, as the basic principles of genetics today showing just how accurate he was.

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Approximate Word count = 1316
Approximate Pages = 5 (250 words per page double spaced)