Scientists have discovered that women are attracted to men who are fond of children. For the most part fairly pointless research—except that what this particular group of scientists has shown is that women can tell who is and is not fond of children just by looking at their faces.

The members of the group in question, led by James Roney of the University of California, Santa Barbara, are part of the revival of a science that once dared not speak its name—physiognomy. In the late 18th century, and during most of the 19th, it was believed that the shape of a person’s head could tell you something about his character. Such deterministic thoughts fell out of favour during the 20th century. Most behavioural scientists thought that environment, not biology, shaped behaviour, and even those who did not could not see how the shape of the head or features of the face could possibly be relevant. What Dr Roney and his colleagues have found is that they are.

Their 39 male subjects, selected from a variety of ethnic backgrounds, were shown 20 pairs of pictures, each depicting an adult and an infant. They were asked to signify their preference for either the adult or the child. Some reported no interest in the child at all. The rest expressed a range of interest, including a few who always preferred the pictures of infants. The men also provided saliva swabs to assess their testosterone levels. The researchers then took digital photographs of the men and doctored the images so that their hairstyles were obscured, and could not affect the judgments of the female subjects.

These were a group of 29 women, from equally diverse backgrounds, who were shown the photographs. They were asked to rate the men according to whether they thought the men liked children, and whether those men appeared masculine and physically attractive. They were also asked to say which men they preferred for short-term and which for long-term relationships. The results, which have just been published in the Proceedings of the Royal Society, confirm that women are very good at reading faces.

The first part of the study provided confirmation of work done previously by other groups, using different methods. When asked to rate the men’s masculinity, the women agreed on who was top and who was bottom, and their rankings correlated with the testosterone levels from the swabs. What was novel was that when asked to rate the men’s liking of children from the photographs, they ranked them in the same order as the researchers had done from the interest the men themselves had shown in pictures of infants.

In physiognomic terms, the first result is easy to explain. Testosterone has multiple effects. When its production rises during puberty, it causes both body and mind to be reshaped, so it is little surprise that the former (square jaws and so on) reflect the latter (lust). But Dr Roney and his colleagues were unable to quantify what it was about the faces of the baby-friendly that signalled this attitude to women.

When asked with whom they would prefer to have a short-term relationship, women tended to pick the high-testosterone males. This makes sense from an evolutionary point of view, since testosterone suppresses the immune system. Like the proverbial peacock’s tail, an excess of testosterone suggests that an individual must have particularly disease-resistant genes in order to compensate. These make desirable partners for a woman’s own genes in her children. The problem with testosterone-fuelled males is that they are less likely to remain faithful to their partners.

By contrast, men who show an interest in children are also likely to make good partners, because they will care for their offspring. The study showed that women prefer these men for long-term relationships. Again, no surprise.

The surprise is this: some men were perceived both as masculine and as interested in children. From an evolutionary point of view, a trade-off between the two would have been predicted. That would produce what is known as an evolutionarily stable strategy in which the child-loving men father fewer babies to start with, but see as many live to maturity because they help to raise them rather than deserting the mothers. From the female point of view, the existence of men who are both hunky and child-friendly might seem too good to be true. For the men involved, it certainly seems like a lot of hard work.