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

The research team, led by Yumnah T. Khan of the Autism Research Centre in the Department of Psychiatry, together with colleagues including Alex Tsompanidis, Carrie Allison, neonatologist Topun Austin, and Simon Baron-Cohen, tested 130 newborns, 67 males and 63 females, at a mean age of just 33 hours after birth. That extraordinarily tight window is the study’s methodological centrepiece. Infants tested at 33 hours of life have experienced almost none of the social world: no extended eye contact, no named gender, no toys, no language, and no deliberate socialisation. Any behavioural difference observed at this stage, the researchers argue, is far harder to attribute to learning than differences measured in older babies, toddlers, or children.

The experimental design was deliberately minimal. Each newborn was presented simultaneously with a video of a human face and a video of a non-social object, while gaze-tracking equipment recorded precisely where the infant looked and for how long. The stimuli were matched in their presentation, and the infants’ spontaneous looking behaviour served as the sole measure. Eye-tracking is the gold standard for interrogating early attention because newborns cannot follow verbal instructions, and their visual behaviour is one of the few channels through which the hidden architecture of their emerging cognition can be observed at all.

The results split into two revealing layers. When the researchers analysed percentage looking time — the proportion of total looking devoted to the face rather than the object — female newborns on average allocated a greater percentage of their attention to the face than male newborns did. The effect size was moderate, at Cohen’s d of 0.40, a magnitude that is meaningful in behavioural science without being dramatic. When the analysis shifted to absolute looking times, an equally nuanced pattern appeared: females showed a genuine preference, looking longer at the face than at the non-social object, whereas males showed no preference for either stimulus.

Crucially, however, the team found no statistically significant differences between the sexes in the absolute amount of time each group spent looking at the face, or at the object. That absence is what elevates the study above a simple headline. The sex difference is not that girls look more at faces in total, nor that boys look less; it is that girls distribute their attention differently between the two types of stimuli. Sex differences in this experiment live in the relative allocation of attention — in the internal comparison an infant appears to make between a social signal and a non-social one — rather than in raw visual appetite.

The significance of that distinction extends to how scientists interpret the causes of behavioural sex differences more broadly. Decades of research have documented on-average psychological differences between males and females, from interests and social orientation to the prevalence of particular neurodevelopmental conditions. But the scientific community remains divided over the engines of those differences. One camp emphasises gender socialisation: from birth, children are treated, spoken to, and encouraged differently depending on their sex, and any observed divergence could in principle be the residue of that immersion. The other camp allows for partial biological contributions, notably prenatal sex hormones such as testosterone, which differ systematically between male and female foetuses and are known to influence brain development.

Newborns are among the very few human populations capable of adjudicating between these accounts, at least in principle. Because infants at 33 hours have had negligible postnatal social experience, a reliable behavioural difference at this age suggests that something occurring before or at birth — prenatal hormones, genetic factors, or differences in maturational tempo — may contribute to the earliest organisation of social attention. The Cambridge team is careful, in its published abstract and plain-language summary, to frame prenatal sex hormones as one possible explanation rather than a proven cause. They also name two credible alternatives that the current design cannot fully exclude.

The first alternative concerns maturation. Male and female foetuses develop on slightly different schedules, and differences in the maturity of visual or attentional systems at birth could produce divergent looking patterns without any specifically social mechanism being involved. A less visually mature infant might, for instance, engage more diffusely with both stimuli, diluting any face preference. The second alternative concerns the stimuli themselves. Low-level visual properties — contrast, motion, complexity, colour, luminance — can drive infant looking independently of whether a stimulus is social. If the face video happened to possess visual features that interact differently with male and female early visual systems, the observed effect could reflect those properties rather than the face’s social meaning. The authors present these explanations not as disqualifiers but as honest boundary conditions on interpretation.

Context strengthens the new findings considerably. Previous research on neonatal sex differences in face preference is described by the team as extremely limited, with the small number of existing studies yielding mixed results, raising methodological concerns, and remaining unreplicated. The new work, with a sample of 130 neonates — large by the demanding standards of newborn research, where recruiting families within hours of birth is logistically fraught — represents one of the most rigorous attempts to date to re-evaluate the question. Conducted at the Rosie Hospital in Cambridge with NHS Research Ethics Committee approval and written informed maternal consent, the study benefits from a controlled protocol, objective eye-tracking measurement, and a sample size that gives the moderate effect observed some statistical credibility.

The longer-term stakes reach into psychiatry and neurodevelopmental medicine. Conditions such as autism are diagnosed more frequently in males than females, and the reasons for that imbalance remain unresolved, spanning biological, diagnostic, and social hypotheses. If sex differences in the earliest attentional orientation toward social stimuli are genuinely present from birth, they may constitute one thread in the developmental fabric that eventually produces sex-differentiated profiles of social behaviour and vulnerability. The authors explicitly note that findings of this kind may help explain why several psychiatric and neurodevelopmental conditions show sex differences in prevalence — a claim offered as a research direction rather than a conclusion, and one that will require longitudinal follow-up linking newborn gaze measures to later developmental outcomes.

For now, the study’s most durable contribution is conceptual. It demonstrates that the relative allocation of attention between social and non-social visual worlds differs on average between male and female humans at the very threshold of postnatal life, while showing that neither sex looks more overall. That pattern is subtle, and the authors resist triumphalism: the effect could reflect prenatal biology, maturational differences, stimulus properties, or some combination of all three. What the study removes from the table, however, is the comfortable assumption that attentional sex differences must be products of the social environment alone. At 33 hours old, most of the social environment has not yet begun. Whatever tips these newborn girls’ eyes toward faces a little more often, it appears to have been installed before the first feed — and scientists now have a sharper, better-powered window into when and perhaps how that installation happens.

Subject of Research: Sex differences in newborn face-looking preferences and their possible prenatal origins

Article Title: Sex differences in face looking preferences at birth

Article References: Sex differences in face looking preferences at birth. (n.d.). https://doi.org/10.1186/s13293-026-00976-9

Image Credits: AI Generated

DOI: 10.1186/s13293-026-00976-9

Keywords: sex differences, newborns, face preference, eye-tracking, attention, prenatal hormones, neonatal development, social cognition, neurodevelopment, autism, infancy, Biology of Sex Differences