Dizygotic (non-identical) twin sisters, image from Wikimedia Commons, ©2006 Dustin M. Ramsey

In the light of the recent hospital admission of the Duchess of Cambridge for an condition loosely associated with female babies and multiple births, I’ve been asked by the Radio 4 programme “More or Less” to calculate the probability that she is pregnant with more than one embryo. I’m somewhat reluctant to contribute to what is already a topic of rampant media speculation, and the attendant intrusive journalism that often plagues issues like this (which, after I had written this post, led to a sad and particularly tragic outcome). Nevertheless, few media articles seem to give links to solid data sources, and some even give rather misleading information, so I’ve overcome my reluctance in order to put some solid statistical facts into the public domain. Simply put, compared to the average, the probability of a mother having twins given that she has this condition is not quite doubled. However, it’s still likely to be a very low number: something like an increase from about 1.5% to a 2.4% chance. For the gory details, read on. Continue reading →

I’m quite pleased that the last “More or Less” question that’s been selected for me happens to be one of my pet topics (I’ve also written a cut-down reply for the magazine section of the BBC news website). The original email was rather long (as is, inevitably, this post), but essentially, the question is this

A listener, Jonathan Trigell has been looking at the Bible. In particular he’s interested in Jesus’ lineage. The Bible says Jesus was in the line of King David – which is important because the Messiah was expected to be of royal descent.

But it also has this to say about David’s son, Solomon

King Solomon, however, loved many foreign women besides Pharaoh’s daughter—Moabites, Ammonites, Edomites, Sidonians and Hittites. They were from nations about which the Lord had told the Israelites, “You must not intermarry with them, because they will surely turn your hearts after their gods.” Nevertheless, Solomon held fast to them in love. He had seven hundred wives of royal birth and three hundred concubines, and his wives led him astray.

Jonathan’s question is this: if Solomon had about a thousand wives and mistresses, assuming he fathered children with many of them, wouldn’t it be the case that by the time of Jesus – many generations later – pretty much everyone in Israel could claim to be a descendant of King David?

It might sound like a question for a pub quiz, rather than a science journal. But the fundamental mathematics behind family trees forms the basis of evolution and genetics, and so cuts to the heart of modern biology.

Continue reading →

Music. Hmm. When I was learning to play an instrument, I found all the rules and jargon extremely confusing. Surely something like music, based on rather simple mathematics, should have an elegant and logical structure to it. Yet music theory seemed like a labyrinth of rules of thumb and historical accident. It was all rather unsatisfying, and I gave up after 6 or 7 years. Nowadays the world wide web has some good information which helps put it in perspective, and I hope I’ve come up with a reasonably jargon-free answer to the following question for my little “More or Less” slot:

I am always amazed by the number of songs one can recognise on hearing the first second or two of music. Since music has a limited number of building blocks and there are mathematical rules for how these can be combined to sound musical, is it possible to calculate the total number of potential opening bars? Surely it must be finite?

To take a stab at this, we’ve first got to establish some ground rules. Continue reading →

A few weeks ago I recorded a slot fot the Radio 4 programme “More or Less“, volunteering to answer any question. A day before the broadcast, they sent me this, from a listener:

 I’m terrified of sharks. People tell me that I’m more likely to be killed by bees, than I am to be eaten by a shark. I’m not convinced. My thinking is that considerably more people come into contact with bees, than they do with sharks. Of these, the bee encounter must be less likely to end in death. Please help…I haven’t entered the sea for about 5 years.

So here’s what I managed to dig up.  Continue reading →