Babies born with a higher genetic risk for chronic obstructive pulmonary disease showed slower lung function growth between birth and age six, but only among children who grew up breathing the dirtiest air. In children living in cleaner areas, the same genetic risk barely registered.
That conditional is the finding. It is not a study showing that genes cause COPD, and it is not a study showing that pollution alone slows lung growth. It is a study showing that one of those mattered mainly in the presence of the other, which is a harder result to report and a more useful one.
