Whereas it appears proven that physical traits are hereditary, the correlation between the genetic code and individual behaviour, intelligence, and health is less concrete and immensely complex. The argument of "Nature vs. Nurture" as a convenient catch-phrase for the roles of heredity and environment in human development is old.
Yet, it remains unclear to what extent phenotypic attributes are determined by the genome or the environment, respectively.
Lucid explanations like "nature endows us with inborn abilities and traits whereas nurture takes these genetic tendencies and moulds them as we learn and mature" did not stop the debate "nature vs nurture".

For instance, the search for "behavioural" genes is a source of never-ending debate. Critics persist that genetic arguments might be abused as excuse for criminal acts, justification of divorce or explanation of sexual preferences ("homophily-gene"). Only few cases of traits detrmined either by nature (genome) or nurture alone are known so far. For instance, some diseases, such as Huntington's disease, are described showing a correlation >99.9% between the identified genetic aberration and the disease-phenotype. On the other hand, most acquired abilities as the ability to speak the mother tongue are entirely environmentally determined: linguists have found that any child (provided that capable of learning a language at all) can learn any human language with equal facility. Virtually all psychological traits however, appear to be an intermediate between determination by nature and by nurture, and emphasis of these influences is rather philosophic than scientific.



The majority of lung cancer patient are smokers, but, vice versa, not all smokers sicken with lung cancer. And not everyone who overeats comes down with diabetes.
Cigarette smoke, diet, and other environmental influences may cause disease, dependently on the individual and the environmental conditions. The Environmental Genome Project (EGP, initiated in 1997) aims to understand why our environment affects people so differently. The human genome now being sequenced, the EGP is working the information to tease out the complicated assortment of genetic variations, environmental exposures, and individual behaviours that determine between health and disease.

Important tools to distinguish between genetic and environmental effects are twin studies. The study of genetically similar (or even identical) persons, i.e., monozygotic (MZ) twins growing up in different environments on one hand and genetically unrelated (by population standards) children growing up in the same family environment, on the other side, help gaining insight into whether environmental differences between families contribute to finally observable ('phenotypic') differences in behaviour and personality. Furthermore, studies can be performed to look at pairs of children who share the same environment, but who differ in their degree of genetic similarity as do MZ and DZ (dizygotic, 'fraternal') twins.

In an article recently published in the journal Biometrics prostate, breast and colorectal cancer were compared in three Scandinavian twin registries for concordance in identical twins and same-sex non-identical twins. Using sophisticated statistical modelling techniques, the researchers concluded that "genetic susceptibility makes only a small to moderate contribution to the incidence of prostate, breast, and colorectal cancer."

Information about types of environmental exposure that affect the risk of cancer should point to genes that might modify this risk, and the identification of genes associated with risk could help to indict previously unrecognized environmental risk factors. Perhaps it is time to drop the competition implied by talking about a debate over nature versus nurture in favor of efforts to exploit every opportunity to identify and manipulate both environmental and genetic risk factors to improve the control of cancer. Through transdisciplinary research, a far greater understanding of how the interactions of social, behavioural, and genetic factors affect health and illness can be achieved.

For further information visit:
Nature and Nurture in Disease by Nancy Touchette
Understanding Genetics: Human Health and the Genome by Kim Matulef
Cancer -- Nature, Nurture, or Both? Editorial in The New England Journal of Medicine - 13jul00 - Vol. 343, No. 2
Nature, Nurture And The Risk Of Depression at Medical News today (04 Mar 2006)
Nature vs. Nurture: Are We Really Born That Way? By Kimberly Powell
The nature vs nurture debate or controversy - human psychology at age-of-the-sage.org
Nature vs Nurture in Intelligence at wilderdom.com