You can probably find hundreds of times the argument in the medical literature that the main cause of asthma is the environment – as genes can not spread within 1 or 2 generations. While this might be true for de novo mutations it is certainly not true with pre-existing variations and recent population dynamics. In a review how asthma came into live, I argued that introduction of antibiotics and improved child care extremely shaped our genome by suppressing purifying selection. In developing countries respiratory infections are among the main killers. Who can help with 1,000 unbiased 100 year old DNA samples to prove this hypothesis? I have an excellent dentist to punch holes in bones.