A fly’s brain is the size of a grain of sand, but Spanish neuroscientist Lucía Prieto Godino is convinced that this tiny organ holds clues to the colossal human nervous system, capable of creating Don Quixote, the smallpox vaccine, and the Pyramid of Cheops. The researcher, born in Madrid 42 years ago, directs her own laboratory at the Francis Crick Institute in London, dedicated to studying neural circuits: the connections between cells on which thoughts, memories, and behaviors depend. “In recent years, we have learned a lot about how the brain works, but we still understand almost nothing about how it evolves. That is the big question of our laboratory,” she proclaims.
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The question is transcendental. The brains of a person, a seahorse, a wasp, a goat, or a toucan are as different as their behaviors. They are so distinct that it is impractical to compare them and draw conclusions. Prieto Godino has chosen to examine much closer and simpler animals: different species of flies that, at first glance, seem identical but act in very diverse ways. “It’s not that we are interested in what flies do. If we find out how their brains evolve, we will be one step closer to understanding how our own brain evolves,” emphasizes the neuroscientist, sitting on the Monumental Bridge of Arganzuela, a Madrid walkway whose shape, a double metallic spiral, resembles the structure of DNA. It’s her lifelong neighborhood.
Modern neuroscience, with a century and a half of history, is still in its infancy. The first complete map of an animal’s brain, presented in 2023, was that of the fruit fly larva. One of its main authors was another Spanish researcher in the United Kingdom, Albert Cardona, from the legendary Laboratory of Molecular Biology in Cambridge, with 16 Nobel-winning scientists, eight times more than all of Spain. That pioneering atlas revealed a structure with barely 3,000 neurons and half a million connections between them. An international consortium achieved the first map of an adult brain a year later: that of the fruit fly itself, with 140,000 neurons and about 55 million connections between them. These are major advances that pale in comparison to the colossal pending challenge, a million times more complex: the human brain, with 86 billion neurons and trillions of connections.
“We want to understand how neural circuits evolve: how it can be that different animals have different brains and different behaviors,” says Prieto Godino, also founder of TReND, an NGO that supports African scientists. The researcher has chosen two species of flies separated by 10 million years of evolution: the fruit fly or Drosophila melanogaster, which eats whatever it is given; and a West African relative that feeds almost exclusively on the fruits of an endemic shrub in the region, Drosophila erecta. By comparing the maps of their brains, Prieto Godino’s team has observed that their different behaviors are not due to a change in the type of neurons, nor even in their number, but in how they connect with each other, especially at some critical points.
A team of Japanese researchers made an astonishing announcement in August 2025. The group, from Nagoya University, managed for the first time to transmit a behavior from one species to another by manipulating a single gene. In their case, they detected the genetic key to the peculiar mating ritual of the Drosophila subobscura fly, in which the female, to accept copulation, requires the male to regurgitate food directly into her mouth. In Drosophila melanogaster, this innate behavior is not observed; instead, courtship is based on music, on sounds emitted by the males with the vibration of their wings. By activating a master gene in certain neurons, the Japanese scientists made Drosophila melanogaster males begin to regurgitate into the females’ mouths before copulating. Their results were published in the journal Science, one of the references in world science.
Lucía Prieto Godino’s laboratory had achieved a similar success even earlier, as confirmed by her colleague Albert Cardona. The researcher and her team not only analyzed why the West African fly has such a marked preference for a specific fruit, but they also managed to transfer that capricious predilection. They made the “eats-everything” fruit fly, Drosophila melanogaster, obsess over that African fruit, through changes in its neural connections. “We did experiments in which we genetically manipulated the flies to try to transfer the behavior from one species to another, and we succeeded,” says Prieto Godino. Their results have not yet been published in a specialized journal, so they are awaiting review by the scientific community.
The Spanish researcher is aware of the evolutionary abyss that separates flies from humans, but she seeks ancestral general principles in brain organization. “Flies have 75% of the genes that cause diseases in humans,” she argues. History proves her right. American Thomas Hunt Morgan began crossing Drosophila melanogaster flies in 1909 to try to understand the mechanisms of inheritance from parents to offspring. In 1933, he won the Nobel Prize in Medicine for demonstrating that genes are stored in chromosomes within the cell nucleus.
There are half a dozen Nobel Prizes awarded to scientists who looked at flies to try to understand humans. American Hermann Muller won the 1946 Nobel for discovering that X-ray radiation caused mutations, thanks to his experiments with flies. In 1995, German Christiane Nüsslein-Volhard and Americans Edward Lewis and Eric Wieschaus were awarded the Nobel for illuminating the genetic control of embryonic development. Again, with flies.
Drosophila specimens were also key to the 2004 awards to Americans Linda Buck and Richard Axel, for figuring out the organization of the olfactory system. Another compatriot, Jules Hoffmann, investigated how these insects fight infections and ended up winning the 2011 Nobel for uncovering the intricacies of innate immunity. Finally, Americans Jeffrey Hall, Michael Rosbash, and Michael Young took the 2017 Nobel after discovering, in flies, the molecular mechanisms that control the circadian rhythm, that internal clock that adapts to the natural cycle of light and darkness. With these antecedents, the dimension of the achievement is better appreciated: transferring a behavior from one species to another, be it a preference for a fruit or a courtship with regurgitation.
― Is it imaginable to transfer a behavior to a human being?
― That question has two parts. Ethically, no, obviously. Scientifically, it’s something so distant… We don’t even fully understand how the neural circuits of a fly work, let alone humans. First, we need to understand very well how everything works, before we can think about transferring.
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― So scientists aren’t going to make us regurgitate before copulating.
― No, nobody needs to worry.
