Some comment about many posts :
a) Supposing Laura Muir is clean (something I strongly think), maybe correct to think she can be the clean WR holder of 1500m (also if I consider Genzebe NOT doped). However, to think she is currently the best in 3000 and 5000m too is ridiculous, since there are not less than 20 African runners (Kenyan or Ethiopia) who are totally clean in their training, and were/are able running well faster than Laura in those distances. The idea all Africans are doped is something, frankly, that can grow in the mind of people not knowing anything about the athletic's reality, and who are not able to individuate the difference among the levels of specific talent.
b) About Samba, I don't agree with El Keniano. If Samba remained in Mauritania, never could have had the opportunity to grow (specialized coach, money for training camps, equipment, etc...). You see what happened with Nicholas Bett (World Champion 2015) and Boniface (silver Olympic medal) : the Kenyan Federation didn't support them in any way, they had the opportunity to grow (under technical and mental point of view) only because their manager, Jukka Harkonen from Finland (who is also the manager of Julius Yego and Manangoi), personally paid their travels, accommodation and the fee of their South African coach. They trained in South Africa for long time, when decided to stay home their performances dramatically decreased. They remained Kenyan as citizenship because Kenya is a great nation, with good social organization, also if nobody takes care, in athletics, of events that are not connected with endurance (from 800m till marathon). But, if you are from Mauritania, where athletics DOESN'T EXIST (they don't have ONE athlete in any event in top 500 in the world last year), and you have great talent, the only way to makes this talent effective is TO CHANGE NATIONALITY, founding some Country which has interest and money to take care of your evolution.
c) Still about Samba : to say that his talent is superior, in all the aspects, to the talent of every other specialist of today, doesn't mean to be a FAN of black people, but simply to have the knowledge for recognizing a potential extra-category athlete, in my opinion the only one who can in the future better the WR of Kevin Young running under 47". In all my life, I remember only Edwin Moses with so great superiority compared with the other competitors, and Samba is still at the beginning of his career. He belongs to the same category of Bolt, Carl Lewis, Bubka, Michael Johnson and few other all-time great in athletics : people with superior talent, who were able to dominate for long periods, because were NATURALLY stronger than the other athletes. Here is not a problem of doping : I'm not sure they were completely clean, but of sure they didn't do anything different from the other athletes of the same period in the same event, and were able to win for years. Simply, THEY WERE MORE TALENTED.