Does the tiny-brained fruit fly experience emotions like fear? New research published in the journal Current Biology suggests that the insects at the very least enter a fear-like state, demonstrating all of the so-called emotion primitives associated with fear—including persistence (the response continues after the threat has passed, such as a fearful human's heart continuing to beat rapidly even after he is no longer in danger), context generalization (the threat distracts you from whatever you were previously doing), and scalability (the greater the threat, the greater the response). "No one will argue with you if you claim that flies have four fundamental drives just as humans do: feeding, fighting, fleeing, and mating," the lead author says in a California Institute of Technology press release. "Taking the question a step further—whether flies that flee a stimulus are actually afraid of that stimulus—is much more difficult."
To test this, the researchers gave hungry fruit flies access to food and then passed a shadow over that food repeatedly. The flies, in turn, jumped and flew away—jumping and flying faster when more shadows passed, and continuing to respond even after the last shadow passed. Still, these displays of context generalization, scalability, and persistence don't quite solve the riddle, one author tells the New York Times: "We can only know that by verbal report. So we can’t scientifically study feelings in any creature but a human." Still, he says in the press release, the research suggests "that the flies' response to the threat is richer and more complicated than a robotic-like avoidance reflex." And if researchers can "identify new molecular players involved in the control of emotion states," as another author puts it, researchers may be able to develop better treatments for humans who are suffering from nervous disorders, reports Discovery. (Check out what male fruit flies get up to when deprived of sex.)