Let me give my opinion, as this is my last reply for some day, because tomorrow I'll go to Kenya again till WCCCh.
I think that the genetical difference is not so important to justify so big differencies. I don't look at African of todays, but at white runners of 20 years ago. During the European Championships of Prague (1978), the EUROPEAN NUMBER 9 (and all were really European, not Maroccan or Algerian with French team) ran 27:41 : NUMBER 9 IN A EUROPEAN RACE. In 2004, the European n. 10 in the seasonal list (after a full year) ran 28:25.
In the junior Italian Team 1982, we had 5 athletes under 14:00 : Mei 13:45, Carenza 13:45, Panetta 13:46, Nicosia 13:51 and Gozzano 13:58. In 2004, the 2nd Italian Junior ran 14:40, almost 1 min slower than 22 years before.
So, what happened ? Simply, our way of life now is completely different. When we speak about "quality of life", we speak about some machine working for us, and the task of a man is only more to press a bottom. THE MODERN TREND IS TO CANCEL EVERY TYPE OF PHYSICAL FATIGUE. With this type of mentality, we cannot have young athletes prepared physically and mentally for an activity where FATIGUE IS THE BASE OF EVERY THING.
I followed Salvatore Antibo in the period 1988-1992, being Italian responsible of 5000/10000m together his coach Gaspare Polizzi. I'm sure that the Antibo 1990 could very easy be the first runner under 27:00 in 10.000, if some other runner could run so fast. When he was 2nd in Seoul OG in 27:23, his final training in Sestriere (2050m of altitude) was 4 times 2000m (rec. 3:00) in 5:45 plus 1 x 1000m in 2:37. In 1990, the same training was 4 x 2000 in 5:28 (difference of 7.5 per km) plus 1 x 1000 in 2:31. So, it's very reasonable to think that his value at the moment was under 27:00, and, being able to finish last lap under 55.0, THE ANTIBO 90 COULD WIN A MEDAL ALSO IN OG 2004. The same for Panetta 1987 : he won World Championships in 3000 SC leading the race from the start, in 8:08 without pushing in the last furlong having more than 30m of gap, 3 days after winning silver medal in 10000m back Kipkoech.
The problem is that now in Europe there is not Antibo and there is not Panetta, there is not Coe, Cram, Ovett, there is not Lopes and Mamede, there is not Abascal and Gonzalez, there is not Garderud (8:08 in 1976), Malinowski, Baumgartl, in Switzerland there is not Deleze and Ryffel, and the level of European Athletic is now very low in middle and long run (except Marathon). And in US, where are Ryun, Wohlhuter, Spivey, Salazar, Nenow, Shorter, Bill Rodgers and a lot of other runners ?
If in 1982 you had 200 runners under 2:20, and 20 years later only 20, is because african runners are too strong or because our society is no more able to produce runners, because there is no more interest in this type of activity?
Don't forget that performances in athletics are a product of social interests. Do you know some white boxeur at the moment in top specialists, after Rocky Marciano, Rocky Graziano, Gene Fullmer and others ? How many years are that no white men agree to catch some kick on the face ?
So, the situation is very clear : if African have interest in running, involving the 50% of young people, and Western People has no interest, involving 0,0005 % of young people, of course the winners are Africans.
In swimming, do you think that there are no African swimmers because of genetical reasons, or because they don't have pools for training ?
In 1960-80, physiology tried to explain that the qualities of a sprinter and/or of a jumper were at the top when the age was 20-24, after had to decrease. This looking at some statistic valueting the age of finalists in OG. But, when athletics became professional, the average of the age of sprinters became 10 years older. At 30 year of age an athlete is yet young, and we have a lot of top runners around 35 years old (Gail Devers, Merlene Ottey, Drummond, the last Michael Johnson, Carl Lewis winning OG at 35, Christie, Allen Johnson and many others). So, the most important input is the social input.
The only way for having again some white at the top is to change again the costumes of our society. But I think that in the future is easier that African change : in the big town nobody runs, and also there the interest in running decreases every year. Kenya, Uganda, Tanzania and Ethiopia recruit their runners from the Mountain areas, and is now more difficult also in those Countries to find good runners, motivated for their instinct and not only looking for the opportunity to earn good money.