Scientists find a gene that impacts how much you smoke.
Apparently it allows you to smoke one cigarette in your mouth while absorbing the nicotine from a second simultaneously through your fingers, as shown in the photo. Or maybe I need to read the article again. :)
That answer lies in part of human chromosome 15, and depends on what is known as allele T of SNP rs1051730. A SNP, or single-nucleotide polymorphism, to give its full name (the short version is pronounced “snip”), is a place where genomes routinely differ from one another by a single genetic letter. In this case, the variation happens inside a gene for one of the receptor molecules that nicotine attaches itself to when it produces its buzz. Based on a study of 13,945 Icelandic smokers, deCODE's researchers showed that having a T in the appropriate part of the gene correlates very strongly indeed with being a heavy smoker. The team estimates that the chance of their being wrong is less than one in a thousand trillion.via The Economist and AP
Not surprisingly, having the T variant also correlates with the chance of a smoker getting lung cancer. Each copy (there may be none, one or two, since one can come from a person's father and one from his mother) increases that chance by 30%. The T variant does not, however, increase the likelihood that someone will take up smoking in the first place. That is either a matter of free will or, if it is genetic, is controlled by genes somewhere else.