character of all
living organisms result from the interaction of environment
For example, the risk of colon cancer is increased by dietary factors
as high fat and low fiber. But a certain genetic allele
(version of a gene sequence) in certain individuals confers a high risk
of colon cancer, even with a low-risk diet.
Experiments designed to demonstrate the genetic or environmental component of a trait generally aim to keep all components constant except the one tested. As a result, someone who studies Down's Syndrome might conclude that the basis of intelligence is genetics; whereas someone studying lead poisoning would conclude that the basis of intelligence is environmental. Actually, all traits -- appearance, development, behavior -- depend on BOTH genes and environment.
Chance also determines the development of an organism. For example individuals with the chromosome abnormality of Down's Syndrome may develop by chance to a wide range of levels -- some develop so badly they die before birth; others have severe heart defects and other physical problems; mental delays vary from severe to minor; some show few physical problems, and can attend college. None of this variation can be predicted from the genes, only from chance effects in development.
Levels of organization in living systemsThe content of the Biology core courses can be viewed as a continuum:
- Cell - Organism
- Population - Ecosystem - Biosphere