In my years of observing runners from a Jamaican point of view,
I have to say that they seem to be two Black running Dynasties:
In the middle to long distances: Kenyans & Ethiopians
In the sprints: Jamaicans
Even today it appears to me that when I watch the top-level sprinters it seems either they are Born in JA or have JA parents / grandparents.
Just an observation.