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Fruit Flies Might Have Building Blocks of Emotions

A new study, published in Current Biology, has revealed the possibility of flies being more ’emotionally intense’ than we would have otherwise given them credit for. The latter’s response to threats has been revealed to be more complex than the typical reflex action. Rather, the reactions of the insects have suggested that they might be having building blocks of emotion; while it cannot be said that flies are emotional beings, they might be having the basic elements thereof.


The researchers of the study subjected flies to fake predators in laboratory to analyse their response, and determine whether they feel fear.

“No one will argue with you if you claim that flies have four fundamental drives just as humans do: feeding, fighting, fleeing and mating,” said one of the authors, William Gibson, in a statement.

“Taking the question a step further – whether flies that flee a stimulus are actually afraid of that stimulus – is much more difficult.”

One of the limitations of this type of study whereby scientists attempt to understand the behaviour of animals with respect to ours is that the animals might be behaving differently in terms of emotions and hence the risk of missing out on relevant occurrences just because its possibility was not even thought of, let alone considered, cannot be ruled out. Studying emotions in animals is therefore tricky. To get by this predicament, the researchers of the study came up with a definition of emotion, as expounded by lead author, David Anderson: “a type of internal brain state with certain general properties that can exist independently of subjective, conscious feelings, which can only be studied in humans”.

Further commenting on the definition, Anderson said: “That means we can study such brain states in animal models like flies or mice without worrying about whether they have ‘feelings’ or not.”

The scientists broke down emotional states into their basic building blocks known as “emotion primitives”, which can be applied to different species. They do not comprehend any particular emotion, and include persistence, scalability, and generalisability.

Persistence means that the response remains for a certain amount of time following the stimulus.

Scalability implies the intensifying of the reaction under repeated stimuli .

Generalisability is about having the same response in different situations and settings.

The aim of the scientists was to observe whether the primitives mentioned are displayed by fruit flies when they are exposed to stimuli of fear; a fake aerial predator represented by an overhead shadow was made to cater for that. It was seen that the shadow caused the flies to react by jumping or freezing, and to be in a state of arousal. When the same was repeated, their response increased. The flies also demonstrated generalisability and persistence when they ignored food available to them until after their arousal levels stabilised.

The responses have not been described as “emotions”, in spite of them being similar to fear in mammals. The researchers did however conclude that the flies responded in a complex manner, and not just out of reflex.


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