Flies' 'surprising mental capacity'
Flies appear to "think" before they act, and - like humans - they take longer to make trickier decisions, a study has found.
Scientists admitted to being surprised by the discovery, which indicates that even insects show signs of intelligence.
Gathering information before deciding on a course of action was previously thought to be the preserve of highly evolved species, such as monkeys and humans.
In a series of tests, the researchers asked fruit flies to distinguish between ever closer concentrations of an odour they were trained to avoid.
When the concentrations were very different and easy to tell apart, the flies acted quickly to move to the end of a chamber furthest away from the strongest smell.
But when they were very close and difficult to distinguish, the flies took much longer to make a decision, and made more mistakes.
Instead of responding impulsively, they seemed to accumulate information, weighing up what their smell sense was telling them before committing to a choice.
Professor Gero Miessenbock, from Oxford University's Centre for Neural Circuits and Behaviour, said: "Freedom of action from automatic impulses is considered a hallmark of cognition or intelligence.
"What our findings show is that fruit flies have a surprising mental capacity that has previously been unrecognised."
The researchers, whose findings appear in the journal Science, showed that a gene called FoxP was involved in the decision-making process in the fly's brain.
The gene was active in a small set of around 200 nerve cells.
Lead author Dr Shamik DasGupta, also from Oxford University, said: "Before a decision is made, brain circuits collect information like a bucket collects water.
"Once the accumulated information has risen to a certain level, the decision is triggered.
"When FoxP is defective, either the flow of information into the bucket is reduced to a trickle, or the bucket has sprung a leak."
Flies with a mutation in FoxP took longer than normal flies to make decisions when odours were difficult to distinguish.
Like a human paralysed by a difficult choice, they became indecisive.
Mathematical models developed to describe the mechanisms of decision-making in humans and other primates matched the behaviour seen in the fruit flies, the scientists found.
Fruit flies have one FoxP gene, while humans have four related FoxP genes.
Human FoxP1 and FoxP2 have previously been associated with language and mental development.
The genes are also linked to the ability to learn fine sequential movements, such as playing the piano.
"We don't know why this gene pops up in such diverse mental processes as language, decision-making and motor learning," Prof Miesenbock said.
"One feature common to all of these processes is that they unfold over time.
"FoxP may be important for wiring the capacity to produce and process temporal sequences in the brain."
He added: " FoxP is not a 'language gene', a 'decision-making gene', even a 'temporal-processing' or 'intelligence gene'.
"Any such description would in all likelihood be wrong.
"What FoxP does give us is a tool to understand the brain circuits involved in these processes.
"It has already led us to a site in the brain that is important in decision-making."