Newborns Show Sex Differences in Attention Within Hours of Birth, Cambridge Study Finds

One of the longest-running debates in psychology concerns the origins of differences between men and women in behaviour, cognition and social development. Are these differences learned, absorbed from a culture that treats boys and girls differently from the moment they are born, or do they partly reflect biological factors that operate before a child has any experience of the social world at all? A new study from the University of Cambridge offers what its authors describe as a unusually direct way into that question, because it examines infants just hours after birth, an age at which postnatal socialisation has barely begun.

The research, published in the journal Biology of Sex Differences, tested 130 newborn infants, each examined only hours after delivery. The team, based at the University’s Autism Research Centre, presented the babies with two videos shown side by side. One was a social stimulus: a human face moving naturally. The other was a non-social stimulus: a Newton’s cradle, the familiar desk toy in which a row of metallic balls swings under gravity and their mechanical properties, transferring momentum from one end of the row to the other. Neither stimulus carried cultural meaning; one simply depicted a person, the other depicted moving objects.

The central finding was that, regardless of sex, newborn infants generally preferred to look at the social stimulus. Human faces, it seems, exert a powerful pull on attention from the very start of life. But when the researchers compared the two sexes, a consistent on-average difference emerged. Female infants spent a greater proportion of their looking time on the face, while male infants spent a greater proportion of their time on the swinging balls. The effect is a difference in averages between groups, not a categorical split, and the researchers are explicit that there is substantial variation within each sex and considerable overlap between them.

The result matters because of its timing. Within hours of birth, an infant has had almost no exposure to gendered clothing, toys, parental expectations or any of the countless cultural signals that shape development in the months and years that follow. If differences in social attention are already measurable at this point, the authors argue, then prenatal biological factors that differ between the sexes during pregnancy, such as sex hormone levels and genetic influences, are likely to contribute to them. That does not mean biology determines everything; rather, it suggests that prenatal factors set up early tendencies that later interact with experience.

The study is, in an important sense, a replication. In 2000, researchers at the University of Cambridge published a study reporting that newborn girls, on average, looked longer at faces while newborn boys, on average, looked longer at objects. That finding was influential but also contested, and scientists in the field called for it to be repeated under more rigorous conditions. Until now, no team had attempted it. The reason is practical as much as scientific: carrying out controlled experimental research on newborn infants is extraordinarily difficult. Recruitment must happen around unpredictable deliveries, testing windows are measured in hours, and every aspect of the procedure has to be gentle enough for babies only recently out of the womb.

The new study was designed to answer those methodological criticisms. Compared with the original 2000 experiment, it used more controlled experimental testing conditions and a more reliable method for monitoring infant gaze. Crucially, the researchers who analysed the videos of the babies’ eyes were blind to two things: the sex of each baby, and whether the baby was looking at the social or the non-social stimulus. This double-blinding of the analysis stage ensured that the expectations of the people coding the data could not bias the results, a safeguard that addresses one of the most common sources of concern in observational infant research.

Yumnah Khan, a PhD student at the Autism Research Centre and the lead researcher on the study, placed the finding in the context of the lab’s broader research programme. Our recent research has also shown that on-average sex differences are present in brain structure at birth and emerge prenatally, she said. This new study tells us that there are not only on-average sex differences in the brain but also in attention and behaviour. In other words, the structural and the behavioural evidence now point in the same direction: some differences between the sexes are detectable before postnatal experience could plausibly have produced them.

Professor Sir Simon Baron-Cohen, Director of the Autism Research Centre, who supervised the study, framed the result as a contribution to one of psychology’s oldest arguments. This study addresses the age-old question of whether nature plays any role at all in shaping sex differences in the human mind and brain, he said. The fact that we observe these differences within hours of birth, before extensive postnatal experience has occurred, suggests that prenatal factors play a role, and that these prenatal factors, sex hormones and/or genes, go on to interact with postnatal experience. In other words, it’s nature and nurture, not nature or nurture. That formulation is a deliberate rejection of the binary framing that has often dominated public discussion of the topic, in which commentators are asked to choose between a fully biological and a fully cultural account.

Other members of the team emphasised the limits of what the study can claim. Dr Alex Tsompanidis, Assistant Research Professor at the Autism Research Centre, noted that sex differences at birth are important as starting points, but that they do not fully determine how children learn and develop in later life, because biological and social factors always interact, contributing to the rich diversity of human societies. Professor Carrie Allison, Deputy Director of the Centre, stressed the statistical character of the finding: the differences do not apply to all male or all female infants, and are only seen when groups are compared on average. Our future research needs to better understand that variation, she said, pointing to the overlap between the sexes as a key target for further work.

The team’s next step is a longitudinal follow-up study, already underway and funded by the K. Lisa Yang Centre for Autism Research at Cambridge, part of the Yang Tan Collective. By following the same children over time, the researchers hope to determine whether these earliest differences in attention contribute to later differences in children’s minds, brains and behaviour. The stakes extend beyond the nature-versus-nurture debate itself. Girls, on average, learn to talk earlier and develop social skills faster than boys, and conditions such as autism, which is diagnosed about twice as often in boys as in girls, may be connected to the same developmental pathways. The researchers hope that by understanding the origins of the earliest sex differences, scientists can better understand neurodiversity and the conditions in which it is expressed. The original study was supported by the Wellcome Trust, the Simon Foundation Autism Research Initiative and a PhD studentship from Trinity College, Cambridge and the Cambridge Trust.

Subject of Research: Sex differences in newborn social attention and their prenatal origins

Article Title: Sex differences in attention are present at birth, study finds

Article References: Sex differences in attention are present at birth, study finds. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: newborn infants, sex differences, social attention, prenatal factors, Autism Research Centre, University of Cambridge, Biology of Sex Differences, face preference, nature and nurture, infant gaze, autism, hormones