The experiments have been performed. For instance, this dopamine receptor has a single nucleotide polymorphism that emerged in the middle east 40000 years ago (and therefore has very different prevalence across ethnic groups) and causes ADHD. There is a just-so evolutionary argument that states that as humanity spread out from Africa, novelty-seeking becomes advantageous as people adapt to new environments. This novelty-seeking is then pathologised as ADHD in the modern world.