As scrump pointed out up top, there are sociological factors that could be suggested for all of the situations you brought up. The first thing you learn in a statistics course (not that your anecdotal evidence is a statistical sample, but for the sake of argument, let’s pretend it is) is that you should never assume causation, even when you have a correlation. For example, most people in hospitals have some sort of illness or another, but it would be erroneous to assume therefore that hospitals cause illness.
So, for instance, it may be that instead of your black friends being genetically predisposed to sports, they simply feel that larger societal pressure to involve themselves in sports or less societal faith that they can be predominantly white jobs such as lawyers and bankers. Not to mention that racism is still a major factor in getting a job, or even living in particular neighborhoods—so you may be mistaking their inability to get jobs like that for genetics.
Coming from an Asian family (here’s my anecdotal evidence) there was always a lot of pressure on my to excel academically. It’s a huge part of many Asian families in the U.S. and that is more likely the cause of the “mathematical Asian” stereotype than genetics.
The same can be said of your Jewish friends—a group that is even more nebulous and less genetically linked than the other “races” you mentioned. It seems extremely unlikely that all Jews share those genetics that cause us to be bankers—considering that we are such a spread out group that has not really been one identifiable race for a long time.
Something else interesting about the racial divide in olympics. Check out this first paragraph of an old NY times article about Kenyan runners:
“When he was 10 years old, Richard Chelimo would run back and forth to school every day from his home in the Rift Valley of western Kenya, the region that has produced many of the world’s greatest distance runners. He had to run. There are no school buses in the rural hills of Kenya.”
Can you imagine an American child doing that? No wonder they’re such good runners in Africa.
Now, obviously that wouldn’t account for any African-American runners your statistics include (the article you linked didn’t seem to mention any, however… interesting!), but the other factors I outlined above can explain some of that, but also, simply the prevalence of African runners in the media might explain it. After all, if you see someone who looks like you on television doing something great, maybe you think to yourself, “Hey, if he can do that, I can do that.” And then maybe you go out and do it.
I’m not saying it’s not possible that genetics accounts for some things. Obviously it does—as scrump cleverly pointed out, “Africans are a hell lot better at standing in the sun for long periods of time, then say, and Irish man.” Just because a concept like Eugenics makes us uncomfortable doesn’t mean we should reject it outright. But most of the notable literature that exists right now (the stuff that I’ve read anyway) suggests that any truth in the stereotypes you’ve pointed out come more from cultural effects than genetics.