Lunch Hour Lectures have been running at University College London since 1942.  It's terrific to know that even at the height of World War II, British citizens wanted to learn about the latest science in an informal setting.

Scheduled for today, the first one for the 2010-11 season has (well, had?) professor of genetics Steve Jones on ... incest. 

His argument is that it is much more common than most people think and you might have (unintentionally) committed it yourself.   “Incest means having sex with a relative - and we all indulge in it, whether we realise or not. On average, two randomly chosen British people are sixth cousins, which means that they share an ancestor who lived in the year of publication of The Origin of Species (1859),” explained Jones.

He invokes Darwin, who married his cousin and was concerned about the possible health effects of inbreeding.    He found, for example, that the offspring of cousins were less likely to find a place in Oxford and Cambridge boat-race crews and also developed an ingenious way of measuring its extent: how often do two people with the same surname marry? In fact the levels of inbreeding in most of Britain, then and now, were relatively low (and are still much lower than in, for example, Spain), Jones says.

Darwin's health concerns were partly justified - rate of illness and early death among the children of cousins is about twice that of the general population, although the actual extent of harm done in developed countries is low. Now we have the molecular equivalents of surnames – stretches of DNA containing particular combinations of letters.

The lecture will explore why inbreeding is an escape from true sexual reproduction, how some creatures abandon sex altogether, and how mating within the family is still surprisingly common in some populations (including some within Britain) although it may, at last, be on the way out.

Says Jones, “Anyone with two identical copies of the same stretch of DNA is likely to have received them by virtue of inbreeding. We can as a result measure the extent to which incest happens in any population – and sometimes the results are surprising. The Pakistani population of Bradford is among the most inbred in the world – but the people of Orkney are also remarkably closely related to their spouses.”

In the western world, the incidence of cousin marriage is going down. One way to observe that is to ask how far away from your own birthplace was that of your partner; and how does that compare for the figures for your parents, your grandparents, and so on. In almost all cases, the distance has increased dramatically, reducing the extent of inbreeding.

“I will discuss this and more and ask why, for hermaphrodite slugs, sex stops at Preston,” said Jones.

So what do incest and folk-dancing have in common?  They are two things you should never try, according to Sir Thomas Beecham.  He didn't think much of brass bands either, unless they were "in the open air and several miles away".

Back to Jones, if you wanted to tune in remotely today, the lecture now says it is on "Eyeing the Brain" by Dr Francesca Cordeiro , UCL Ophthalmology, so perhaps incest is just a tad too controversial for lunch.  Or they changed the date.  

Check out the entire Lunch Hour Lectures schedule here.  
Video archive here.