Almost all unmarried pregant women say that the fetus resembles the father, study finds

A study asked expectant parents who they thought their fetus resembled during an ultrasound. Results showed that mothers, but not fathers, were more likely to say the fetus resembled the father. In the absence of any valid visual cues for establishing resemblance, 93% of women who were not married said that their fetus resembled the father, compared to 68% of married women and 47% of married men. The paper was published in Evolution and Human Behavior.

Without dedicated medical tests, a man cannot be completely sure that he is the biological father of his partner’s child. This is known as paternity uncertainty, and it has been an important issue throughout human evolution. It remains a relevant topic even today. Unlike females, who can be certain of their biological connection to the child due to internal gestation, males face a degree of uncertainty because fertilization occurs internally.

This uncertainty may have shaped a number of male reproductive strategies and behaviors. Men may have evolved psychological mechanisms such as jealousy, mate guarding, and sexual possessiveness to reduce the risk of investing resources in offspring who are not biologically theirs.

Paternity uncertainty also helps explain cultural practices such as norms surrounding female chastity, strict mate surveillance, and patrilineal inheritance. It has been linked to increased paternal investment when resemblance to the father is emphasized. When paternity confidence is high, men are more likely to provide support, protection, and resources to their children.

In response to this dynamic, mothers may have developed a tendency to claim that their child resembles the father, even when no actual resemblance exists. Such a strategy could help reduce paternity uncertainty and secure paternal investment. Study author Carlota Batres and her colleagues sought to determine whether this tendency appears even before birth. Specifically, they investigated whether pregnant women, in the absence of visible traits like skin color or facial features, would still say that their fetus resembled the father.

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Study participants included 190 expectant parents who visited an obstetrics and gynecology clinic, mostly during their routine 20-week pregnancy ultrasound. Their average age was 31 years. Eighty percent of the couples were married, while 20% were in a relationship.

Participants completed a questionnaire that asked them who they thought the fetus resembled. Response options included: “Mother,” “Father,” “A relative of the mother,” “A relative of the father,” and “Does not look like anyone.”

Among fathers, 49% said the fetus resembled themselves, while 51% said it resembled the mother. In contrast, only 26% of mothers said the fetus resembled themselves, while 74% said it resembled the father.

The researchers then analyzed responses by relationship status. Among married men, 47% said the fetus resembled themselves, compared to 58% of men in a relationship. Among married women, 69% said the fetus resembled the father, compared to 93% of women in a relationship who were not married.

“By claiming phenotypic similarity with the father, mothers are reducing paternity uncertainty and, consequently, securing investment for their offspring from when they are in utero,” the study authors concluded.

The study sheds light on an interesting behavioral tendency with likely deep evolutionary roots. However, it should be noted that the data came from a small group of expectant parents from a single clinic and is based on responses to a single question. Studies on larger groups and those that phrase the question and response options differently, might not yield identical results.

The paper, “Investigating perceptions of fetal resemblance,” was authored by Carlota Batres, Amy Mullen, Sonya Krofl, and Lauren Trainor.