Sources of Human Variability
- biological inheritance, shaped by
- mutations, allelic differences
- genetic drift
- natural selection
- prenatal environment and fetal "programming"
- artificial or cultural selection
- nutrition and malnutrition
- quality of life and health care
- pollution and toxin exposure and other stressors
- education
- cultural environment
- social environment
- family environment and upbringing (especially before age 5)
- child abuse and neglect
- accidental, industrial or intentional injury, mutilation, or change of the body
While nearly all of the variables listed above are at least partially determined or affected by genetic factors, few of them are controlled by simple Mendelian inheritance. Most are polygenic or are determined by a complex combination of genes and early environment. Essentially, genes provide proclivities and potentialities continuously involving feedback mechanisms with the environment throughout life, but especially during prenatal and early childhood.
Many genetic differences (polymorphisms) have little effect on health or reproductive success, but serve to statistically distinguish one population from another. Researchers in the field of population genetics have been using these to elucidate ancient migrations and relationships between population groups.
Another purely genetic set of individual differences are the blood types and immune types we all carry. While some may carry mild advantages or disadvantages in terms of risks of particular diseases, the primary life-or-death significance comes when we attempt to transfer blood or organs from one person to another. Our immune system is designed to recognize these human differences with great sensitivity and enforce our individuality.
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