Here's his "official" biography:
Mike French is a child prodigy who re-wrote the time space acceleration theory at the age of 11. He also has issues with his mother.
Mike is a genius and should know a thing or two about the way the world works. Sadly he had little time for anything approaching a normal childhood and is a naïve, emotionally repressed 20-something instead. Mike's going through a kind of delayed puberty and it falls to Paul and the team to mentor him through the murky waters.
This includes the proper time and place to goof off and watch old episodes of 'Doctor Who' and 'The Benny Hill Show'......
It will be the contention of Toobworld Central that Mike French is the great-grandson of Nigel "Niles" French, a man-servant who was seen for a few episodes of 'Family Affair' back in the 1960s. Nigel French was brought into the Davis household in New York City to care for the nephew and nieces of globe-trotting architect Bill Davis while the original valet, his own brother Giles French, served at the pleasure of Her Majesty Queen Elizabeth during a world tour. (I'm thinking that was the cover story for a stint with 'Torchwood'. Someday I'll get around to writing that theory up!)
We really didn't get to learn very much about Nigel French in the short time he was on the show. But it's possible that he had been married at one time much earlier in life (He was 64 while in the service of the Davis household) and sired a son to carry on the family name. Giving enough time for new generations of the French line to emerge, I'd say it's pozz'ble, just pozz'ble, that Dr. Mike French could be Nigel French's grandson.
The best part about making the genealogical distance between the two characters so great is that it's unlikely that any mention of Mike's great-grandfather should come up in the 12 episodes that were produced.
One - as in me, er, I - can only hope.