if ADHD is genetic, why isn’t there a blood test for it?
In: Chemistry
If it is genetic, it is caused by a combination of genes, and we don’t really know which ones. If it were just one gene, it would be really easy to determine, and also would have been acted on by selection long ago. Most complex traits (intelligence, attention span) and even many simple ones (height) are caused by many different genes acting in different ways. All the easy genetic wins have already happened, basically; if one gene did something unambigously good, it lived, and all the others died out. We’re now left with genes that point in different directions for different things, so selection on them is difficult.
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