Babies perk up to sounds of ancient hazards By Bruce Bower
Babies have an ear for primeval dangers, a new study suggests. “There is something special about evolutionarily threatening sounds that infants respond to,
By age 9 months, infants pay special attention to sounds that have signaled threats to children’s safety and survival throughout human evolution….Those sounds include a snake hissing, adults’ angry voices, a crackling fire, thunder claps and — as a possible indicator of a nearby but unseen danger — another infant’s cries.
Noises denoting modern dangers, as well as pleasant sounds, failed to attract the same level of interest from 9-month-olds…tens of thousands of years of evolution have primed infants’ brains to home in on longstanding perils, the scientists propose.
… 11-month-olds rapidly learn to associate fearful faces with images of snakes and spiders “There is now a coherent argument that infants are biologically prepared in at least two sensory systems to learn quickly which evolutionarily relevant objects to fear,”
Further work needs to check an alternate possibility, he adds: that babies learn soon after birth to associate sounds of snakes and other ancient threats with adults’ negative reactions.
…babies are already sensitive to sounds that have denoted threats dating back to the Stone Age. The auditory system, unlike the visual system, is nearly mature at birth.
In response to ancient danger sounds, infants:
- experienced a bigger drop in heart rate
- larger eye blinks as measured by electrodes
- increased turning toward the speakers or parent, all indicating that they were paying more attention.
- Babies didn’t cry or otherwise get upset while listening to danger sounds.
…infants first recognize adults’ expressions of fear between 5 and 7 months of age. Learning what to fear begins around that time, and proceeds more easily and quickly for threats with ancient pedigrees.