Society is gradually shifting towards gender equality. Yet most of us still carry a badge of differential gender roles that is intimately tied up in our identity: our names.

Throughout the English-speaking world, most women choose not to retain their surnames after marriage. And children are typically given their father’s surname.

This practice inconveniences women. It potentially reinforces gender roles and the unequal status of women and men within marriage and society.

Why, despite decades of feminism, does this persist?

A new theory

A new journal article has proposed an explanation for this behaviour using evolutionary theory. The University of Western Ontario’s Melanie MacEacheron argues that women changing their surname acts as a signal of fidelity to their husbands.

This enhances the likelihood that both the father and the paternal grandparents will invest in the children of these marriages. Enhanced investment then confers an evolutionary advantage on children by providing them with survival and reproductive benefits.

This pleasing of husbands and in-laws is potentially at odds with pleasing maternal grandparents, who are also an important source of investment in children. However, a woman can always be certain that the child she gives birth to is hers. Therefore, the child’s maternal grandmother can be also certain that her grandchild is hers.

A man does not have the same degree of assurance of his paternity. The maternal grandfather can only be certain his grandchild is his if he is certain that his wife was faithful to him.

Similarly, paternal grandparents can only be certain that their grandchildren are theirs if their son is also certain of his paternity. As a result, paternal grandfathers are the least certain of genetic relatedness out of all grandparents since they have two uncertain links to their grandchildren.

Given this uncertainty, any reassurance of their genetic relatedness – such as women changing their surname – will increase the likelihood of investment in their grandchildren.

This evolutionary explanation does not suggest that changing one’s surname is a biologically based behaviour. Rather, evolution has favoured the underlying inclination to solicit investment from husbands and in-laws. Changing one’s surname after marriage is just one way to do this.

Nor does this explanation require mothers to make decisions consciously about soliciting investment from husbands and in-laws. The psychological mechanisms underlying these processes may operate outside of our consciousness. We would not expect that women will state soliciting investment as their reason for changing their surname after marriage.

In a study of unmarried university students in the US, 31% of women intended to change their surname to their husband’s for reasons relating to devotion and family unity. And 28% intended to change their surname to their husband’s due to tradition.

Marital surname change serves as part of a general strategy for maximising the offspring’s fitness. Therefore, this evolutionary argument is not contradicted by the practice of marital surname change not being universal. The theory might suggest, however, that evidence of soliciting investment through deference to husbands and in-laws using other means is likely to be found across cultures.

If women changing their surname does act as a signal of fidelity, as MacEacheron’s theory argues, then we should find evidence that men perceive it in this way. Research has found that men tend to have negative views of women who retain their surnames after marriage. They are perceived as being less attractive and worse mothers, and less committed to the relationship.

If seeking investment from husbands and in-laws is a reason for marital surname change, then women who are less in need of investment should be less likely to change their surname after marriage. Research has found that women who are wealthier and have a greater capacity to earn money are less likely to approve of taking their husband’s surname.

While this evidence is consistent with the theory, there might be an alternative explanation for this relationship. Perhaps women who have a greater capacity for financial independence are generally more assertive and independent. Therefore, they might also be less willing to submit to the wishes of their husbands and in-laws.

However, lower assertiveness and independence among women who change their surnames after marriage would suggest that surname change might be an act of submission to husbands and in-laws. This submissiveness could be behaviour selected by evolution to solicit their investment.

Is it plausible?

It is difficult to prove conclusively whether MacEacheron’s evolutionary explanation is correct.

Women changing their surname might be more simply explained by factors relevant to the specific cultures in which they occur. But saying that cultural norms explain the behaviour does not explain these behaviours in the ultimate sense, because it leaves unanswered the question of why these norms exist in the first place.

If this evolutionary explanation is correct, it does not imply that women are morally obliged to yield to their husbands’ and in-laws’ preferences for the sake of securing investment from them. “Is” does not imply “ought”. If anything, evolutionary explanations remind us that our behaviour is influenced by unconscious drives and is not always the result of rational deliberation.

The forces of biology and evolution that influence many of our behaviours have no concern for what is right and wrong. Since these forces often act outside our conscious awareness, becoming aware of them might allow us to free ourselves from the influence that they exert over us.

At the very least, evolutionary theory helps understand why we are the way we are. Recognising the animal roots of human behaviour might serve to remove the gloss of legitimacy on cultural norms that are often taken for granted.