Everything is heritable, smoking edition:

"But this interpretation [that smoking parents cause children to become smokers] foolishly neglects to consider the genetic component of parent-child similarity. Table 7.2 summarizes reports of two twin studies, an adoptive study, and a family study. In all these studies, the offspring of smokers were adults at the time they were surveyed. Smoking's heritability averaged 43%, whereas smoking's rearing environmental variation was close to zero. [Shared rearing variation (c^2): N/A  (family, Eysenck (1980)); <0% (Twin, Cannelli, Swan, Robinette, & Fabsilz (1990)); <0% (Twin, Swan, Carmelli, Rosenman, Fabsitz, & Christian (1990)); <0% (Adoptive, Eysenck (1980)); mean: 0%] In other words, effects of rearing variation (e.g. parents' lighting up or not, or having cigarettes in the home or not) were nil by the time the children had reached adulthood. In Eysenck's (1980) report on adoptees, the smoking correlation of biologically unrelated parent-child pairs was essentially zero (r = -.02). Parental smoking may influence a childs risk through genetic inheritance: The role of parents is a passive one-providing a set of genes at loci relevant to smoking risk, but not SOCially influencing their offspring."

--pg204 of Rowe 1994, The Limits of Family Influence: Genes, Experience, and Behavior