ACCORDING to some accounts, a lot of men are bringing up children unaware that they are not the biological father. The figure of 10 per cent or more is often bandied about for the proportion of children involved, but how well does it stand up?

To find out, anthropologist Kermyt Anderson of the University of Oklahoma, Norman, dug through studies going back to 1949 that reported what fraction of purported fathers could be ruled out by blood, genetic or antigen tests.

Of those, 31 looked at the results of paternity tests conducted to resolve legal disputes in which the man suspected the woman of cheating: 30 per cent of these men could not be the fathers. Applying this figure to the population as a whole depends on knowing what proportion of men have doubts. That's a sensitive thing to admit, Anderson points out.

Another group of 22 studies involved genetic or other research in which there was no such prima facie suspicion of non-paternity: in these studies, the presumed father was not the biological parent in only 1.7 per cent of cases.

On the basis of this analysis, Anderson says that the 10 per cent figure "appears inflated". The real number is elusive without a systematic study that tests paternity regardless of whether a man has doubts. The paper will appear in Current Anthropology.