Thomas Hunt Morgan, a biologist at Columbia University in New York, started researching Drosophila melanogaster because they were cheap and easy to work with. Nothing pointed to them having uniquely exceptional traits. 

In his lab in 1910, well before scientists knew what DNA was, he extracted chromosomes from Drosophila and analyzed how genes could be passed on through generations. Thanks to these discoveries establishing genetics as a scientific discipline, he won the Nobel Prize in 1933. British researchers soon followed suit, launching the first fly facility in Cambridge, rearing hundreds of flies in empty glass milk bottles, and studying how genes control physical traits.

“To some extent, it’s happenstance” that fruit flies became a research subject, said Elizabeth Gavis, a professor of molecular biology at Princeton University.

But all of these scientists were onto something. Fruit flies are convenient to study because they’re small, easy to handle and store, and reproduce quickly. They can lay up to 30 to 50 eggs a day which hatch within two weeks. That makes them grandparents in less than a month, and researchers have entire family trees in much less time than working with, say, mice. Fruit flies also only have four pairs of chromosomes, three of which handle most of the coding genes. Compared to mice which have 20 pairs, it’s much easier to track genetic changes in Drosophila, according to Gavis.

Today, we know more about Drosophila than most other animals on this planet. Scientists decoded its full genome as well as a complete connectome of all the neurons in its brain. They can tweak the mapped-out genetic and neural components, allowing them to ask the big, fundamental questions about how organisms work.

“We want to understand the basic biology of how cells work, of how cells are organized into tissues, of how things like, you know, a brain work,” said Gavis. 

Since Morgan, fruit flies have brought nine other scientists a total of five Nobel prizes. Experiments on fruit flies have helped us understand how X-rays cause mutations in genes, how genes tell cells how to develop into embryonic cells, how an animal’s innate immune system is triggered, and how the circadian clock works inside cells. The discoveries in Drosophila teach us about the many animals that separate humans and flies on the tree of life and what unites us as animals of planet Earth. 

After all, we are all more alike than we might think. 

Our similarities with fruit flies reach deep into the genetic level. 60% of fruit fly genes can be found in people, and 75% of the genes implicated in human diseases are found in fruit flies. That makes them a perfect model to tackle questions about human health, according to Steven Russel, head of the department of genetics at the University of Cambridge. 

He works in that original Fly Facility at Cambridge, which has now become internationally renowned. In two temperature-controlled rooms—one at 18°C and one at 25°C—the Fly Facility houses more than 60,000 tubes homing millions of Drosophila with all sorts of different mutations for different behaviors or physical appearances. Every morning, a lab member comes in early to prepare over 100 liters of fly food in a gigantic kettle. Thankfully, they have a simple taste: A mix of cornmeal, sugar, yeast, and agar will do.

“You can do incredibly sophisticated things with flies,” said Russell. “You can get them addicted to alcohol, you can get them addicted to cocaine, you know, find genes that are responsible for that underlying sin.”

Like humans, fruit flies have been found to use alcohol to self-medicate and enjoy sex. Since coffee keeps flies awake and older flies tend to sleep less, fruit flies have been used to study sleep—research on fruit flies has detected the genes that make us hungry when we’re sleep-deprived. It’s even possible to insert human genes into a fly’s genome and observe how it takes over the function of the insect, according to Russell. Drosophila have helped researchers understand epilepsy and seizures, understand the genetic origin of Alzheimer’s, and unpack how cancer cells spur. In fact, fruit flies are often used to screen and test new drugs for humans. They are even studied in space.

“Anyone [who has spent] any small amount of time, working and looking at flies, it is no surprise to any of us—they are incredibly sophisticated and marvelous creatures,” said Russell.

The more scientists have learned about fruit flies, the more they’ve been humbled by all the complex feats they’re capable of. Drosophila, it seems, live a rich, kaleidoscopic inner life. And scientists are now appreciating this beyond its human application. 

“They have inner cognitive processes that are happening that are really interesting to study in themselves,” said Clara Howcroft Ferreira, a neuroscience professor at Northumbria University in the United Kingdom. 

When asked to distinguish between two odors, for instance, fruit flies take longer to choose the more similar the two are. In this experiment, fruit flies display “a hallmark of perceptual decision-making,” said Ferreira. It signifies a cognitively complex choice where tougher decisions take longer, rather than the popular belief of an instinctive reaction. It’s not too different, Ferreira said, to when she decided to move to London for her new job: starting over, moving the kids. “It took me quite a while to come to the decision, to measure the pros and cons,” said Ferreira. “And then basically realizing that flies also do this, this is really exciting.” 

Fruit flies also read cues from the other individuals they’re with to aid their decision-making, according to Ferreira’s latest research. When threatened with an incoming dark disk (resembling being swatted), flies on their lonesome froze. But in groups of two to 10, they were less likely to freeze, as if their fear was buffered by the social context. They also were more likely to resume flying if their peers did, seemingly understanding a social cue for safety.