Biological Explanation
Initiation
The role of genetics - family and twin studies estimate the heritability of tobacco smoking to be between 39% and 80%. Vink et al. (2005) studied 1,572 Dutch twin pairs. They found that for both males and females individual differences in smoking initiation were explained by genetic (44%) and environmental (56%) influences. Likewise, a US study of 348 identical twin pairs and 321 same-sex fraternal twin pairs estimated the heritability for regular smoking to be 42% (Bordman et al., 2008).
Maintenance
The effects of nicotine - Vink et al. also reported that nicotine dependence was influenced by genetic (75%) factors, which suggests that regular tobacco use is linked more strongly to individual differences in nicotine metabolism. Nicotine affects brain chemistry by activating nicotine acetylcholine receptors in the brain, which leads to the release of dopamine. These chemical reactions create short-lived feelings of pleasure for the smoker, who then experiences impairment of mood and concentration within hours of their last cigarette as nicotine levels drop in their blood. These effects can be alleviated by smoking another cigarette. Smokers repeat this cycle many thousands of times in order to avoid withdrawal symptoms when not smoking.
Pre-natal exposure to nicotine - research suggests that mothers who smoked heavily while pregnant were more likely to have children who, should they start smoking, were more likely to become addicted.
Relapse
Twin studies suggest that the ability to quit smoking is also subject to genetic influences. For example, Xian et al. (2003) carried out a twin study to test whether genetic risk factors contributed to failed attempts to quit smoking. They found that 54% of the risk for quit failure could be attributed to heritability. Research (e.g. Uhl et al., 2008) has also attempted to identify the specific gene clusters associated with quit success and with nicotine dependence, with the aim of matching specific anti-smoking treatments with the smokers most likely to benefit from them.

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Biological, cognitive and behavioural (learning) explanations of smoking and gambling, including initiation, maintenance and relapse.