Newborn girls might spend more time looking at a human face, while infant boys might prefer looking at objects, a new study has found.

Researchers from the UK's University of Cambridge observed the result within hours of the newborns' birth -- much before social expectations based on gender start taking place.

According to them, prenatal biological factors differing between the sexes during pregnancy -- such as hormone levels and genetics -- likely contribute to the observed sex-based differences in what grabs a newborn's attention.

The 130 infants were presented with side-by-side videos containing a social stimulus, namely a human face with natural movement, and a non-social object -- a set of metallic balls swinging due to gravity and their mechanical properties.

The study, published in the journal Biology of Sex Differences, found that, regardless of sex, newborns generally preferred to look at the social stimulus.

"When analysing percentage looking times, on average, females allocated a greater percentage of time looking at the face relative to males," the authors wrote.

Alex Tsompanidis, assistant research professor at the Autism Research Centre at the University of Cambridge, said, "Sex differences at birth are important as starting points, but we need to remember that they don't fully determine how children learn and develop in later life. This is because biological and social factors always interact, contributing to the rich diversity of human societies." In 2000, the team published that girls at birth, on average, looked longer at faces, while boys looked longer at objects.

Scientists in the field have since then called for a replication of this study. However, no research team has attempted this until now, since it is very challenging to carry out research on newborn infants, the researchers said.

The findings also contribute to the nature vs nurture debate in psychology, which is concerned about how much of an individual's characteristics is due to genetics (nature), and how much due to environment (nurture).

An interaction between one's genes and their environment is thought to make up a diverse range of traits across species.

"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," author Simon Baron-Cohen, director of the Autism Research Centre, who supervised the study, 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," Baron-Cohen said.

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