GROWING up without a father around can present a lot of challenges to a girl. Quite apart from the behaviour problems and lower academic achievement that can accompany father absence, there are also potential consequences for sexual behaviour and relationships later in life: daughters who grow up without a father in their home are more likely to reach puberty earlier, have sex earlier and are more likely to get divorced.
A study published last week looking at the physical attributes of women whose father was absent could provide clues as to why these things happen.
Dr Lynda Boothroyd and Professor David Perrett at St Andrews University asked web-recruited volunteers to rate the appearance of the faces of three groups of women: those whose parents had a good relationship as they were growing up, those whose father was absent, and those whose parents stayed together but had a poor relationship.
The study, published in Proceedings of the Royal Society, found that father absence and parental marital strife were associated with less attractive, more masculine faces in daughters. The researchers also found that these women tended to have less feminine body shapes and more body fat than women whose parents had a good, stable relationship.
So why should separated or warring parents be associated with masculinity in daughters? One theory is that stress during childhood could raise cortisol levels, and there is some evidence that this can have masculinising effects.
Another possibility is that hormones are responsible for both marital strife and masculinity in daughters: high parental testosterone levels or sensitivity could increase the chances of marital problems and desertion by the father, and if passed on to daughters could lead to a more masculine appearance.
At this stage, however, it is impossible to establish the direction of cause and effect. "We're probably looking at interaction between genetics and environment," says Dr Boothroyd, now at Durham University.
The researchers suggest that the link between parental relationships and appearance could have repercussions for the daughters' choices of partner and success in relationships later in life, because, in general, less attractive women need to have lower expectations of partner quality or be willing to settle for short-term relationships.
"If you're more masculine it's going to be harder to get a good quality mate, in terms of what you've got to bargain with," says Dr Boothroyd. "This could be driving certain elements of why women who grew up without fathers are less likely to be in long-term relationships."
Dr David Waynforth, of Durham University, studied the effects of father absence in a Mayan population in Belize and found that sons of absent fathers had more masculine faces. He speculates that a masculine appearance and hence high testosterone levels may be a response to help overcome the disadvantage of being without a father, enabling sons to push their interests more aggressively to make their way in society.
Dr Waynforth doesn't think that women raised without a father around would be at a reproductive disadvantage. "While they may through higher facial masculinity be rated a bit lower for physical attractiveness, they should be more driven to seek sex and more sexual partners," he says, "assuming testosterone affects female sexual behaviour in the same ways that it seems to affect male sexual behaviour."
Another potential influence on a woman's sexual behaviour is the quality of relationships she has with men as she grows up. Professor Bruce Ellis, of the University of Arizona, found in a long-term study of girls in the United States and New Zealand that daughters whose fathers were absent tended to reach puberty earlier, and were much more likely to become pregnant as a teenager than daughters with two resident parents. He found that this early sexual activity was more pronounced in girls who were deprived of a father from early in life. Even among the girls who lived with their fathers, those who had a closer father-daughter relationship delayed sexual relationships for longer. Prof Ellis suggests that the quality of a girl's relationship with her father, especially in the first five or so years of life, becomes internalised and sets the stage for her later sexual behaviour. Could the same be true of the physical effects that we see?
"The key research agenda for the future will be to assess facial masculinity and attractiveness in girls early in life," Prof Ellis says, "and then to determine whether girls who experience father absence and poor mother-father relationships change over time to become more masculinising and less attractive."
For all the disadvantages to girls of being without a father when they are growing up, they can take some comfort in the fact that they are likely to be more attractive than those whose parents stayed together in spite of marital strife.
The St Andrews University study rated daughters of warring couples as the least attractive and they were deemed less healthy looking than those of separated parents, perhaps as a result of ongoing family tension. But as Dr Boothroyd says: "It's nothing new to suggest that long-term psycho- social stress is not good for children."
• To help with Linda Boothroyd's research, go to www.boothlab.org