Genetic explanations for the Initiation of addictions
Heritability of addictions such as alcoholism and gambling can be studied through family and twin studies. The presumptions of twin and family studies are that if family members share similar behaviours, then the degree to which the behaviours are caused by genetic factors can be examined. There are two types of twins, identical and non-identical. Identical twins are monozygotic (MZ) as they came from the same egg, and therefore share an identical set of genes. Non-identical twins are dizygotic (DZ) as they come from two different eggs that were fertilised at the same time, and as a result their genes are no more alike than any brother or sister's. Twins can also differ in the environment that they are brought up in. Some twins may, rarely, be separated at birth and therefore have very different upbringings. If researchers are able to find MZ twins who have been raised apart (i.e. same genes but different environments) then they will be able to distinguish between the influence of genes and environment on a certain behaviour. If MZ twins who have been raised apart booth show the same behaviour, then the behaviour is probably genetic; but if only one of them has that behaviour then it may well be caused by the environment. The degree to which twins and family members share a behaviour is termed a concordance rate, with 1 (or 100%) being entirely genetic, and 0 (or 0%) being entirely environmental. McGue (1999) found a concordance rate of 50-60% for alcohol addiction, and Agrawal & Lynskey (2006) found a concordance rate of 45-79% for addiction to illicit drugs. This means that just over half of the factors that cause addiction to alcohol are genetic in origin, as are half to three-quarters of the factors causing addiction to illegal drugs. A problem with this conclusion, however, is that the genetic link may be for behaviour disorders rather than addiction, and these behaviour disorders may manifest as many...
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