PASADENA, Calif., May 15 (UPI) -- A new study suggests fruit flies demonstrate a primitive form of fear. The involved science opens the door to defining and studying emotions in animals.
Trying to identify emotions in animals is a complicated process. Humans have a tendency to anthropomorphize animal behaviors.
"There are two difficulties with taking your own experiences and then saying that maybe these are happening in a fly," lead study author William T. Gibson, postdoctoral scholar at the California Institute of Technology, explained in a press release.
"First, a fly's brain is very different from yours, and second, a fly's evolutionary history is so different from yours that even if you could prove beyond any doubt that flies have emotions, those emotions probably wouldn't be the same ones that you have," Gibson said. "For these reasons, in our study, we wanted to take an objective approach."
To move past these semantic roadblocks, Gibson and his colleagues decided to break down the idea of emotion into more definable components -- into basic building blocks. Researchers decided to call these building blocks "primitives."
"That means we can study such brain states in animal models like flies or mice without worrying about whether they have 'feelings' or not," Gibson said. "We use the behaviors that express those states as a readout."
A primitive fear must be associated with a stimulant or trigger that would cause a fearful response in humans.
Primitives (or the emotional building blocks) of fear include a few concepts. One primitive is the principle that an emotional trigger is scalable -- 10 gun shots should produce a fear response greater than the response to a single gun shot.
Another primitive is the cross-contextual nature of the trigger. A gun shot will scare or startle a subject (eliciting a recognizable behavioral response) regardless of their current circumstances -- whether a subject is eating lunch or taking a stroll.
Trans-situationality is another primitive principle, whereby sounds that mimic a gun shot (like a car backfiring) will have similar effects.
When researchers applied all these primitives to the scenario in which a swatter or arm waves or shoos away a fly, Gibson and his colleagues confirmed these primitives were consistent with the response to a large shadowy object swinging overheard.
"These experiments provide objective evidence that visual stimuli designed to mimic an overhead predator can induce a persistent and scalable internal state of defensive arousal in flies, which can influence their subsequent behavior for minutes after the threat has passed," Gibson's colleague David Anderson said. "For us, that's a big step beyond just casually intuiting that a fly fleeing a visual threat must be 'afraid,' based on our anthropomorphic assumptions. It suggests that the flies' response to the threat is richer and more complicated than a robotic-like avoidance reflex."
Their research is published in the journal Current Biology.
"Our work can get at questions about mechanism and questions about the functional properties of emotion states," Gibson concluded, "but we cannot get at the question of whether or not flies have feelings."