Anything you can do externally will tend to evolve out. That's why humans can't make their own Vitamin C and half of them need glasses. Keeping a trait in the population does require keeping up the selective prrssure, which is eugenics.

What is this, eugenics from first principles?

Are you suggesting that it would be advantageous for humanity to evolve to live in London circa 2000?

Larry Niven played with this in one of his stories; a time traveller from the far (and highly polluted) future has to use mechanical breathing assistance, because the levels of CO2 in the air in the past weren't high enough to prompt the breathing response properly (human breathing is controlled largely by blood CO2 levels).

Asthma is so common that this is not only easy to test, but has been. That's what the article was about.

Anyway, by your own line of thinking, wouldn't sensitive lungs be an advantage? The incentive to find cleaner air is also breaking away from the pack. Since humans are social creatures, that's more likely to look like new leadership for followers who have their own reasons to break away.

Every civilization in history has started out that way. It takes more than mere brute force to beat the competition. Survival is just as much about picking your battles and working smarter.