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