Would you choose a good meal over sex?

When given a choice between food and sex after being denied both, most individuals will opt for a good meal over a good time, according to a new study that reveals some of the biological factors underlying decision-making.

The research, published in the journal Current Biology, found that when confronted by the age-old behavioural conflict, the impulse to mate was overridden by the urge to eat in experiments on fruit flies. The tiny flies, also known as Drosophila, are ideal avatars in the world of neuroscience because their brains exhibit complex behaviour that offer a simpler model for obtaining insight into human cognition. The brain of a fruit fly consists of around 100,000 neurons — just a fraction of the 86 billion found in humans.

“We are often exposed to conflicting situations where we must prioritize one goal over others,” said Carolina Rezaval, the research team leader at the University of Birmingham. “For an animal in nature this could mean having to choose between feeding, mating or fighting for resources. How does the animal know what to do? The fruit fly Drosophila is a great experimental system to understand how crucial behavioural decisions are made in the brain. We can identify neural elements that direct behaviours with great resolution and decipher the underlying mechanisms.”

Researchers found that hunger overpowered other urges in male flies that were separated from food and females for an extended period of time, with the “behavioural tipping point” occurring at around the 15-hour mark of starvation. After satisfying the need for sustenance, male flies returned to more amorous interests, often within a matter of seconds.

Using genetic tools during live experiments, researchers were able to pinpoint the precise neurons responsible for prioritizing competing impulses in the brains of their tiny subjects.

“The neurons that tell the fly to go and eat, or to go and mate, are essentially competing with each other,” explains Scott Waddell, a professor at Oxford University who collaborated with researchers. “If the need to eat is most urgent, the feeding neurons will take over, if the threat of starvation is less, then the urge to reproduce will win.”

The study found the behavioural choice, while generally consistent, could be influenced by extenuating factors, such as a subject’s energy levels and the quality of the food source. Hungry flies may rebuff bad food in favour of mating with a female.

The team hopes a better understanding of the underlying mechanisms at work in fruit flies will yield new knowledge about the human brain and its impulses, said Saloni Rose, a PHD student and one of the main contributors to the study.