IF YOU relish tales of the macabre, you need look no further than the British monarchy. Kings and queens regularly dispatched those who sought to dethrone them. Shared blood was no guarantee against dark deeds — in fact, the death of Edward III in the 14th century precipitated two centuries of kings exterminating their cousins, a period referred to as the Cousins’ War.

But, amid the dynastic dastardliness, our murderous monarchs seem to have been obeying Darwinian rules. They executed close but non-linear relatives, such as cousins and uncles, in order to give closer kin, such as sons or daughters, a better chance of success. More intriguing, however, is that rulers never removed more from the gene pool than they put in. So, a king with one son — who possesses 50 per cent of the king’s genes — would not kill five cousins, who each share 12.5 per cent of his genes. But he might kill three — reckoning that the removal of 37.5 per cent of royal genes is compensated for by the newly strengthened position of his son’s 50 per cent.

A team of anthropologists from Cambridge University and Indiana State University first “scored” the direct genetic output of each monarch. This comprised 1 for himself or herself, plus 0.5 for every legitimate child and 0.25 for each grandchild. Then the researchers added up the genetic relatedness scores of victims, usually cousins or cousins’ children. Henry IV, who reigned from 1399 to 1413, and whose own score was 5.0, had a killing score of 0.28. Edward IV, who reigned from 1461 to 1483, had a personal score of 6 but, with a brother among his victims, amassed a killing score of 0.91.

They conclude in their paper Culling the Cousins: Kingship, kinship and competition in mid-millennial England that “. . . executioners never sacrificed linear relatives (children or grandchildren) nor executed collateral relatives in excess of their own legitimate nuclear relatedness”. The paper will appear next month in the journal The History of the Family. “All evolution is, is getting your genes into the next generation,” says Professor Kathleen Heath, from Indiana State. “But those genes can sit in other people’s bodies, which is why we favour our own relatives over non-relatives. But there are times when our relatives can be close competitors.” Which is where the hooded man with the axe comes in.

To get rid of more genes than you pass on, Heath says, risks evolutionary suicide. And British monarchs, whether they had calculated or not, were too smart for that. Heath also suspects that the Ottoman Empire, or wealthy, family-run companies would show a similar, deadly pattern. The stakes are so high — be it the throne or money — that bumping off blood rivals begins to look viable.

“Nobody’s suggesting that kings were running around with a calculator in 1420,” Heath says, “but these figures do seem to fit a pattern that (Darwinian) theory predicts.”

SCIENCE NOTEBOOK is nothing if not hip. So let me sign off this week’s dispatch from the frontline by toasting “molecular mixology”. This is a highly scientific, rigorous, calculated approach to . . . mixing cocktails.

Moto, a buzzing hangout in Chicago, is home to a particularly inventive mixologist, called Homaru Cantu. His signature drink involves vaporising a vanilla bean with a laser. The vapour is deposited on the inside of a glass, which is then filled with red wine. The drink is said to be delicious with beef.

A Washington restaurant has perfected a “dirty martini”; mix olive juice, vermouth and gin with xanthan gum and calcium chloride, then drop into a sodium alginate and water solution to form a olive-shaped blob. The blob reverts to liquid in the mouth. The news leaves me shaken and stirred.

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