A poor example as Autism can be driven by environmental factors such as the MMR immunization drugs. We recently witnessed our own child regress after having one, and narrowly avoided further regression with a 2nd. I know it hasn't been scientifically "proven" to everyone's satisfaction, but my wife's experience with autism is with children who regressed to autistic-like symptoms after those immunizations.
Asthma as it turns out can be driven by environmental causes as well. Extreme levels of stress can create an initial condition of psycho-somatic asthma in children. Additionally, it's now known that cockroaches present in the home can cause children to develop asthma.
A poor example as Autism can be driven by environmental factors such as the MMR immunization drugs.can.
Extreme levels of stress can create an initial condition of psycho-somatic asthma in children. Additionally, it's now known that cockroaches present in the home can cause children to develop asthma.
can can
What the twin studies show is that there are environmental as well as genetic factors in these conditions.
If they were entirely genetic, we'd see a much higher concordance between identical twins, approaching 100%. If it were entirely environmental, we'd see a concordance rate in identical twins closer to the rate between non-identical twins.