Evolutionary Evidence – Do Babies Fear Snakes?

There is disagreement about whether animals are born with a fear of life-threatening stimuli or whether the evolutionary system biases attention toward potentially threatening stimuli .  One way to test these hypotheses is to explore how babies experience fear.

Over several trials, 6-9 months old infants were shown videos of snakes or elephants, paired with nonsensical fearful or happy voices (Thrasher & LoBue, 2016).  While experiencing the video/voice combination, babies experienced a startle probe – an unexpected, white screen on the video, during which their startle reflex was measured. Dependent measures included startle eye blink magnitude (a pure measure of valence; greater magnitude = greater unpleasantness), startle latency (time from baseline to peak startle), heart rate change, and time spent looking at video.

Relevant findings are below with interpretations explaining whether these findings indicate babies innately fear snakes or whether their attention is biased toward snakes.

Result #1: When babies heard the fearful voice, their startle magnitude was lower when watching the snake video compared to the elephant video. This indicates that babies experienced more unpleasantness during the elephant/fearful than snake/fearful trials.

• If babies were afraid of snakes, their startle magnitude should be higher when watching the snake, particularly while listening to a scary voice!
• Why? If babies were born with a fear of threatening stimuli like snakes, when they see the snake, they should already be tense and their SNS system would be activated. Thus, when the startle probe happens their reaction should be even more intensified if they fear the snakes.  This is like our reactions during a scary movie – we are already in activated state because of the scary movie, and then when something happens, we jump!  But this did not happen!

Result #2: Babies’ startle magnitude AND heart rate change was lower during the snakes/fearful voice than during the snakes/happy voice.

• After we identify a threatening event, our heart rate and startle magnitude increase (refer back to defense cascade here).  If babies were afraid of snakes, their startle magnitude and heart rate should be GREATER when watching snakes with a fearful voice than a happy voice.
• The drop in heart rate during the snakes/fearful voice might suggest that infants were exhibiting an orienting response (described in defense cascade here).

Result #3: When babies heard the happy voice, their startle magnitude did not differ when watching elephant versus snake videos.

• If babies feared the snakes, then the babies should have shown GREATER startle magnitude to the snakes than to the elephants when hearing the happy voice.

Result #4: Babies exhibited shorter startle latencies for snake versus elephant films, indicating they reached peak startle quicker when watching the snake films.

• This finding indicates babies identified the snakes faster than the elephants, not necessarily that the babies feared the snake more than the elephant. A shorter startle latency results in faster detection of potentially threatening stimuli.

What do all these findings mean?  Well, Thrasher and LoBue (2016) state these findings provide evidence that babies do not inherently experience negative emotions or fear toward snakes, as some evolutionary theorists might suggest.  In line with Öhman and colleagues, this study supports the idea that babies are not born with innate fears, but instead are born with the capacity to acquire fears of certain events.  And studies on children support this. In line with earlier findings on the visual search paradigm, young children will quickly locate a snake in a grid of other non-snake photos (LoBue & DeLoache, 2008), suggesting children are predisposed to respond quickly to snakes, but not necessarily to fear them.

Dr. LoBue’s website includes her blog about babies and information about her lab.