A study published by the California Institute of Technology (Caltech) appears to show that fruit flies exhibit behavior that indicates that they can feel fear. Whether they can experience real emotion is something that is probably impossible to determine. However, based on the results of this study, fruit flies show fear the same way a human would. The results of the study were recently published in Current Biology.
Building Blocks of Emotion
According to one of the authors of the study that fruit flies show fear, David J. Anderson, the building blocks of emotion are referred to as emotion primitives. These include things like scalability and persistence.
He likens this to travel along a hiking path and seeing a rattlesnake. When you see the snake, your heart rate increases and will continue to pound for a time even after the snake has gone. This shows persistence. Scalability is shown by the amount your heart would pound if you happened upon 10 rattlesnakes. Presumably, your heart would pound even harder and faster and it would take a longer amount of time for it to return to normal.
The lead author of the fruit flies show fear study is postdoctoral fellow at Caltech, William Gibson. Gibson states that flies have the same basic drives that humans have: fighting, feeding, mating and fleeing. However, whether fruit flies will run because of fear is hard to determine. It appears that they have tried, however, and feel that the study showed that flies do show fear based on the show of scalability and persistence.
Fruit Flies Show Fear of Shadows
The researchers placed hungry fruit flies inside a chamber and then recorded the results when a shadow was passed over the food. They noted that the fruit flies show fear by running and jumping away. Even after the shadow passed, the flies continued to run, showing persistence. When they increased the number of shadows passing over the food, the flies moved away more quickly, indicating scalability.
Researchers noted that the flies would travel away from their food sources when the shadows appeared, but would shortly return. The longer the shadows appeared, the faster the flies ran away and the longer it took the flies to return to the food source, despite being hungry.
Gibson feels that although it may be impossible to say for certain that flies run away because of fear rather than instinct, since they cannot verbalize, he feels that the study shows that the fruit flies show fear based on the parameters of basic emotion. More studies are planned.
