The genetic predisposition to develop restrictive airways disease can be inherited. During the 1950s and 1960s new medications permitted the survival of severely ill asthma patients who wouldn't otherwise have lived to reproductive age. Then those asthmatics had kids, and their kids had kids, and we are now in the third and fourth generation in some cases. Thus, the tendency to acquire asthma upon exposure to allergic insult is disseminated through the population. Unfortunately, some of these kids get seriously ill, especially when they come into contact with the cigarette smoke and cockroach refuse that are endemic in the worst parts of the inner city, and sometimes their cases aren't followed as closely as they should be. And so we have black children dying in growing numbers.
Before anybody asks what the basis is for makign statements like this: my views were developed in conversation with the clinical researchers at the National Jewish Hospital and Research Center, the nation's foremost center for investigation of respiratory and immune disordes.
During the 1950s and 1960s new medications permitted the survival of severely ill asthma patients who wouldn't otherwise have lived to reproductive age. Then those asthmatics had kids, and their kids had kids, and we are now in the third and fourth generation in some cases. That's certainly a plausible explanation. I also think having ancestors who lived in cold climates selected for genes that more easily tolerated environmental insults, such as living in poorly ventilated shelters with open fires for heat in winter.