New research indicates there are two specific genes driving people to consume more or less caffeine. It found people who carry a so called "high-consumption" variation of either gene appear to drink more coffee than those who carry a "low consumption" variant.
Authors of the study say people don't really suspect it but genetics play a role in a lot of behaviors and now it turns out that how much caffeine we consume may be one of them.
The study appears in PLoS Genetics.