It is probable that Parkinson's has more than one root cause. As does CTE. But repeated blows to the head is a "likely" cause even if not a definitive one. Scientists - when they are in research mode - are always looking for the Holy Grail of causes, the smoking gun. Because they didn't see the brain scan 2 minutes after a boxer is knocked unconscious, they'll claim his memory loss is "not conclusively" tied to the uppercut he received in the fifth round. But when they're on the other side of research and are in getting a new drug to the marketplace mode - that smoking gun is not always needed. Ever see the small print on some Big Pharma TV ads where they say - Why this drug produces positive results on your rash is not fully understood but it works - or words to that effect. Funny how that is. There are people with Parkinson's who never played football or were a boxer, so yeah, multiple causes. But sometimes, just sometimes, the obvious cause is The cause. Good article.