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Sources of human variability[edit | edit source][edit]

Identical twins share identical genes. They are often studied to see how environmental factors impact human variability, for example, height difference.

Environmental Sources
- prenatal environment
  - nutrition and malnutrition
  - disease of the mother
- subsequent factors
  - quality of life and health care
  - pollution and toxin exposure and other stressors
  - education
  - social environment
  - climate
  - family environment and upbringing (especially before age 5)
    - child abuse and neglect
  - accidents
    - accidental, industrial or intentional injury, mutilation, or change of the body
Genetic Sources
- biological inheritance
  - mutations, allelic differences
  - mental abilities
  - physical abilities
  - genetic drift
  - natural selection
  - prenatal environment and fetal "programming"
  - blood types/immune types
- Epigenetics

A skin color map of the world from data collected on native populations prior to 1940, based off of the von Luschan chromatic scale 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.^[1] 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.