A study of newborn infants found that female newborns spent proportionally more time looking at a person’s face than male newborns when shown side-by-side videos of a woman’s face and a moving toy, researchers report — a result the team says is unlikely to be driven by social experience and therefore points to early biological influences on attention.
What the researchers did
Researchers tested 130 infants aged between about eight hours and three days old at the Rosie Hospital in Cambridge. Each baby was settled on a parent’s or carer’s lap while watching a laptop screen that displayed a young woman’s face on one side and a Newton’s cradle toy on the other. An eye tracker recorded where the infants looked as the clips played.
Both boys and girls showed a preference for the human face over the toy, but girls favoured the face more strongly on average than boys did. The study appears in the journal Biology of Sex Differences.
Authors’ interpretation and limits
Because the infants were tested within the first day or few days after birth, the investigators argue that cultural learning or socialisation is an unlikely explanation for the sex difference observed. The authors suggest that biological factors — including genetic influences or differing prenatal exposure to hormones such as testosterone — are plausible contributors to the pattern.
“This is a very active and heated debate in the field of sex differences: what are the causes behind sex differences and how early in life are they present?” said Yumnah Khan, a PhD student at the Autism Research Centre at the University of Cambridge. “What our research shows is that at least some differences are present at a small scale very early on in life.”
The team emphasised the results describe average differences across groups and do not apply to every individual. There was substantial overlap and variation within males and females, the researchers note, and the small differences observed at birth are unlikely to rigidly determine later abilities or interests.
Why this matters
The findings feed into a long-standing debate about how much early behavioural differences between sexes reflect biology rather than upbringing. A detectable difference in attention at the start of life could bias the kinds of experiences infants seek or receive, potentially contributing over time to population-level trends observed later in development. The authors, however, caution against overinterpretation: early tendencies are only one factor among many that shape growth and learning.
- Sample: 130 infants
- Age range: ~8 hours to 3 days
- Stimuli: video of a young woman’s face vs a Newton’s cradle toy
- Setting: Rosie Hospital, Cambridge
- Publication: Biology of Sex Differences
| Measure | Value |
|---|---|
| Total infants tested | 130 |
| Age at test | 8 hours–3 days |
| Primary comparison | Face video vs Newton's cradle toy |
| Location | Rosie Hospital, Cambridge |
| Journal | Biology of Sex Differences |
For scientists who study early brain and behavioural development, the study provides a carefully controlled demonstration that measurable attentional differences can be present extremely early. For clinicians and educators, the take-away is not that sex determines outcome, but that biological predispositions could modestly shape experience from the outset.
Future work will need to investigate the biological mechanisms behind the effect and to follow infants over time to see whether and how small early differences in attention relate to later social, cognitive or communicative development. Until such longitudinal and mechanistic data are available, the authors and outside commentators urge caution in extrapolating from a short laboratory assessment to long-term abilities or destinies.
Reporting on early sex differences provokes strong public interest; this paper contributes evidence that nuanced, modest group differences can be measurable at birth while underscoring the complexity of translating such findings into broader claims about gender, ability or social roles.
