While thinking about the biological basis of addiction I started wondering if there had been twin studies done with addiction. I found a study done by McGue et al. (1992) that investigated between twins of different sexes and alcohol dependence. Here is the abstract:
Male monozygotic cotwins of probands with alcohol abuse-dependence (n = 85) were more likely than male same-sex dizygotic cotwins (n = 96) to report alcohol, drug, and conduct disorder problems. For women, rates of problem behavior did not differ between monozygotic (n = 44) and same-sex dizygotic (n = 43) cotwins. Opposite-sex dizygotic twin data (n = 88) revealed significant cross-sex transmission; alcohol problems were greatest among male cotwins of female probands. For men, proportion of liability variance associated with additive genetic factors was significantly greater when proband had an early (h–2 = .73 ± .18) rather than late (h–2 = .30 ± .26) age of onset. For women, heritability did not vary as a function of proband’s age of onset, and the pooled estimate suggested little genetic influence (h–2 = .00, SE not computable). Findings suggest that genetic influences may be substantial only in the etiology of early-onset male alcoholism.
The results of this study are fascinating because, contrary to some theories, biology was only a significant factor in early-onset male alcoholism. This may just be correlation and not causation! There is much more behind addiction than other neuropsychological diseases. There seem to be family trends in addiction but this research seems to disprove a large part of addiction is based on biology. There must be an environmental aspect influencing the onset of addiction. Personality is also another interesting aspect of addiction onset. There have been many studies on the interaction personality and addiction presented here and in class, but there is the question of what determinants play into personality, environment and/or biology?
In conclusion, addiction is not a simple equation of biology and environment; instead it is a complicated and possibly inexplicable combination of factors.