Why do human beings get tired? Because they still haven't recovered from the sperm's epic journey from the testes to the Fallopian tube (The Great Sperm Race, Channel 4, Monday 23 March 9pm). The salmon's 1,000-mile return to its spawning ground is a mere flick of the tail compared with the distance sperm have to travel. And forget the ancient heroes, too. The Spartans at the Hot Gates? Why, that's only a warm-up. The siege of Troy? A package holiday. Semen, not Greek men, should have been Homer's theme.
"Glen has no idea of the miracle of engineering tucked away in his pants." Apparently, 1,000 sperm are produced with each heartbeat. "What would a testicle be like if we cut it in half?" asked Dr Allan Pacey with a little too much relish. The innocent Glen skipped happily under the sheets with Emily, last seen chopping up a tomato. Frank Sinatra sang All the Way.
Packed as tight as commuters on a rush-hour Tube train, the sperm sense something is wrong. "But they have no idea of the horror that awaits them," the voiceover observes gleefully. And then it begins. A great shaking and tumult before high-speed propulsion along the tubular tracts of the epididymis. If we scale the sperm up to the size of humans, it would be the equivalent of travelling 15 miles in two seconds along a swimming-pool flume.
Glen's sperm is not welcome in Emily's vagina. Millions perish in acid seas. Those that make it through now have to climb a mountain. Try scrambling up a slippery ladder at the same time as thousands of others; a ladder that reaches a mile into the air. And at the top? The cervix. "Sperm hell." A place of wrong turnings, dead ends and blocked exits. Those that do not get trapped, squashed or crushed wriggle through the carnage before emerging on to the vast plains of the uterus, there to be met by leukocytes, "the elite assassins of the immune system".
As few as 20 make it to the Fallopian tube, where there is a brief respite before the egg rises like a moon, drawing them with lily-of-the-valley perfume. Last scene of all which ends this strange eventful history is the race to fertilise the resplendent sphere. There can be only one winner. And the victor's reward? Its head explodes. That's the only way it breaks through the outer layer of the egg.
This was The Apprentice without the softening influence of Alan Sugar. To think our being here is the result of one sperm that got lucky. One slip, one wrong turning, one brush with the enemy, and I wouldn't be writing this and you wouldn't be reading it. That's what Dickens' Dick Swiveller would call a "staggerer". It was awe-inspiring stuff and made me think seriously, for a minute, about giving up sex. That's the trouble if you use actors to play the part of sperm. You can't help feeling that every climax is a form of mass murder.
I don't suppose it does their careers much good either. "And what was your last part?" "Three millionth sperm on the left. Look at the expression I manage to get into my flagellum as it twitches its last." "Yes, thank you. We will be in touch."
Being born, though, isn't always a prize. Twenty-year-old Kirsten was nearing the end of her sentence in Holloway (ITV, Tuesday 24 March 9pm). She didn't want to leave. "I really do like it here," she grinned. "I know when I'm going to eat and where I'm going to sleep." For many of the girls featured in this film, prison was the only source of stability in their otherwise chaotic lives.
One girl tried to kill herself. "No, the belt wasn't tied to anything, it was just round her neck," an officer explained to a medic on the other end of the line. "No, it was just round her neck. No, it wasn't fixed to anything. It was round her neck." Eventually she managed to make the medic understand what had happened.
The girl in question was put on the at-risk register when she was three months old. At 13 she was in care and had already made three attempts on her life prior to the incident with the belt. Round her neck.
When Kirsten was released, she faced the prospect of homelessness. "Can I come back in?" She was met by a much older man who had bought her a crate of vodka. Later that day, she was arrested for being drunk and disorderly.
How did we get to this state when, in 1959: A Panorama Guide (BBC Four, Friday March 8pm), everyone thought Britain was becoming more open, free and fair? The perils of the vagina are nothing to what lies outside it.