I don't know whether the speculated reasons for the gene's benefits will pan out. But the benefits do seem real. And that finding suggests two things. First, we should be careful about designating diseases and disease genes. Traits that are harmful in one setting can be helpful in another. Advantages or "defects" that we think of as natural may actually be products of our cultural decisions. As Eisenberg puts it, we might "begin to view ADHD as not just a disease but something with adaptive components."
Second, our society may be the wrong place to assess a gene's evolutionary harm or benefit. As the authors note, "[N]on-industrialized or subsistence environments … may be more similar to the environments where much of human genetic evolution took place."
This doesn't mean ADHD is wonderful. Genes that promote fat storage may have been similarly advantageous in subsistence environments, but obesity is still a curse. The lesson of the Ariaal study is simply that society can adapt to genes instead of the other way around. Maybe we don't have to screen and chuck embryos for every "disease" gene, or drug the kids once they're born. Maybe we can put ADHD kids in educational settings more like the dynamic environment of our nomad forebears. And maybe we can raise kids with fat-storage genes in settings less full of food.
If it wasn't too hard for our ancestors, is it really too hard for us?