Last night's viewing: Michael Johnson: Survival of the Fittest, Channel 4 Storyville: Hitler, Stalin and Mr Jones, BBC4

Johnson's discovery of his own slave ancestry was part of the process

I hadn't heard of Jimmy "the Greek" Snyder before I watched Michael Johnson: Survival of the Fittest, but then, since 1988, he hasn't had much of a public profile. He lost his job that year after saying that black athletes were better because they'd been "bred to be that way", a remark that was instantly condemned by all. What Jimmy had failed to understand – beyond the fact that such a thing wouldn't be sayable in any form for years to come – was that if anybody was going to say it they had probably better be black themselves. And last night, give or take a few very important reservations, that was what Michael Johnson was saying. The Olympic gold medallist wanted to understand why it was that so many of the fastest sprinters in the world have slave ancestry, and he was prepared to edge towards hazardous ground to get his answer.

It was a cautious film, properly concerned to acknowledge how important culture and personal qualities are in the development of athletic excellence. But it also addressed an unpalatable possibility: that the very cruelty of the slave trade, its indifference to human suffering and its waste of human life, might have conferred an unexpected genetic advantage on those who survived. Partly, this was unnatural selection, the rigours of the slave caravans and the middle passage killing off the weaker individuals and leaving the strong. But there was also an element of selective breeding, with slave owners treating their captives as an improvable livestock.

Johnson wasn't blind to the awful irony involved here, that a kind of accidental eugenics might have contributed to the humiliation of Nazi fantasies about eugenic supremacy, after Jesse Owens had enraged Hitler by taking four golds at the 1936 Berlin Olympics. But there was a further twist too. After meeting a biologist who had studied the unexpected rebound in the elephant seal population after near-extinction, Johnson floated the idea that a seriously stressed group might find itself unusually free of detrimental genes. And when that quality was combined with the unusual level of genetic exchange brought about by slavery (that indifferently mixed populations that might otherwise have stayed separate), the result could have been an evolutionary bounce. In another rebuke to Hitler, miscegenation may have been part of the story.

It was hard to know how you might go about proving any of this, and there was an anxiety that such a theory might open a door to things you might not want admitted at all. But within its limitations (the genetics was pretty broadbrush stuff), it was fascinating and often moving, with Johnson's discovery of his own slave ancestry part of the process. Perhaps its very existence was the most interesting thing about it, proof that what was unsayable in 1988 can now be addressed without paranoia, and with a reasonable confidence that it won't be maliciously twisted out of shape. There might be further to travel but we've come quite a long way since then.

Family history was also at the heart of George Carey's Storyville film Hitler, Stalin and Mr Jones, which investigated the tale of Gareth Jones, a journalist-adventurer who carved himself out an interesting niche as advisor and investigator in pre-war Russia, Germany and Manchuria, where he was finally shot by bandits. Or possibly the Soviets, who'd been enraged by his genuinely courageous exposure of Russian famine. Or possibly the Japanese, who thought he was a spy. A little over-portentous in style and distinguished by the most surreally inappropriate use of music I've encountered for months, this was nonetheless an engrossing film, a story of personal bravery and shabby intellectual betrayal by Soviet fellow-travellers, further lifted by Jones's Zelig-like brushes with Hitler, Lloyd George and William Randolph Hearst. George Carey goes further than most people to make his films and he always brings something valuable back.

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