Today, it’s the humble fruit fly that delivers yet another blow to creationist dogma.
Creationists insist that all species were created in their present form, complete with fixed behaviours, as though every instinct was hardwired in a single act of creation. But science has shown—yet again—that reality is very different. A tiny change in a single gene can profoundly alter behaviour, rewiring brains and shaping the way species interact and reproduce. And because mating behaviour is central to forming reproductive barriers, such genetic shifts drive the very process of speciation that creationists deny.
The culprit gene here is fruitless (fru), shared by both Drosophila melanogaster and D. subobscura. Yet, despite the shared gene, their courtship rituals couldn’t be more different: male D. melanogaster woo females with wing vibrations, while D. subobscura males present a drop of regurgitated food.
Scientists at Nagoya University have now shown what happens when you swap the fru gene from D. subobscura into D. melanogaster: the flies abandon their ancestral wing song and instead adopt the food-gifting ritual. The switch isn’t magic—it’s a straightforward change in neural wiring. By lengthening the dendrite of an insulin-secreting neurone so it connects with the courtship neurone, the behaviour is fundamentally altered.
What this experiment does is striking: it replays evolution in the lab. It shows exactly how a behavioural shift could have arisen when these species diverged from a common ancestor. It also demolishes the tired creationist mantra that “macro-evolution” is impossible. Here we have behaviour—controlled by genes, reshaped by neuronal architecture—evolving right before our eyes.
The Evolution of Fruit Flies. Fruit flies (Drosophila spp.) have become one of biology’s most powerful models for studying evolution, genetics, and behaviour. With over 1,500 species spread worldwide, they illustrate how quickly lineages can diversify when new ecological opportunities arise.And this is just one example among thousands. Every fresh discovery in genetics, neuroscience, and evolutionary biology widens the gap between evidence and creationist fantasy. Where science uncovers mechanisms, creationism offers only denial. Where evolution provides predictive power, creationism clings to dogma. The fruit fly, in its tiny way, has once more exposed creationism for what it is: a superstition masquerading as science.
- Rapid lifecycles: With generations lasting just 10–14 days, fruit flies evolve quickly, allowing researchers to observe evolutionary changes in real time.
- Global dispersal: Although many species are specialists, feeding on particular fruits or habitats, others (like D. melanogaster) are cosmopolitan generalists, following humans around the globe.
- Speciation in action: Different Drosophila species have distinct courtship behaviours, pheromones, and reproductive barriers. These differences often emerge from small genetic changes that alter sensory perception or behaviour—exactly the kind of process demonstrated in the Nagoya study.
- Evolutionary laboratory: By comparing closely related species, scientists can reconstruct how new traits, behaviours, and reproductive barriers evolved, providing living evidence for the mechanisms of speciation.
- Human relevance: Because many genes are conserved between flies and humans—including those controlling brain development and behaviour—fruit flies are more than just pests; they are windows into the shared machinery of life.
In short, fruit flies are not only a classic evolutionary success story, but also indispensable test subjects for demonstrating how small genetic tweaks can produce large evolutionary consequences.
The research is described in a press release from Nagoya University and is published in Science.
First transfer of behavior between species through single gene manipulation
Scientists strengthen brain cell connections to enable gift-giving courtship behavior in fruit flies.
Researchers in Japan have genetically transferred a unique courtship behavior from one fruit fly species to another. By turning on a single gene in insulin-producing neurons, the team successfully made a species of fruit fly (Drosophila melanogaster) perform a gift-giving ritual it had never done before. The study, published in the journal Science, represents the first example of manipulating a single gene to create new neural connections and transfer behavior between species.
In nature, most male fruit flies court mates by rapidly vibrating their wings to create sound patterns or “courtship songs." However, Drosophila subobscura has evolved a very different strategy: males regurgitate food and offer it as a gift to females during courtship. This behavior does not exist in closely related species such as D. melanogaster.
These two fruit fly species diverged about 30-35 million years ago. Both have a gene called “fruitless” or "fru" that controls courtship behavior in males, but they use different strategies—one species sings and the other gives gifts. The researchers found the reason for this difference: in gift-giving flies (D. subobscura) insulin-producing neurons are connected to the courtship control center in the brain, while in singing flies (D. melanogaster) these cells remain disconnected.
Scientists have successfully transferred gift-giving courtship behavior from Drosophila subobscura to D. melanogaster males. They genetically engineered insulin-producing neurons in D. melanogaster to produce FruM proteins, causing these cells to grow long neural projections and connect to the courtship center in the brain.
When we activated the fru gene in insulin-producing neurons of singing flies to produce FruM proteins, the cells grew long neural projections and connected to the courtship center in the brain, creating new brain circuits that produce gift-giving behavior in D. melanogaster for the first time.
Dr. Ryoya Tanaka, co-lead author.
Division of Biological Science
Graduate School of Science
Nagoya University, Nagoya, Aichi, Japan.
The researchers inserted DNA into D. subobscura embryos to create flies with heat-activated proteins in specific brain cells. They used heat to activate groups of these cells and compared the brains of flies that did and did not regurgitate food. They identified 16-18 insulin-producing neurons that make the male-specific protein FruM, clustered in a part of the brain called the pars intercerebralis.
The researchers identified 16-18 insulin-producing neurons in Drosophila subobscura that express the male-specific protein FruM. When they activated FruM expression in insulin-producing neurons in D. melanogaster, these cells grew new neural connections and successfully transferred gift-giving courtship behavior to this species for the first time.Our findings indicate that the evolution of novel behaviors does not necessarily require the emergence of new neurons; instead, small-scale genetic rewiring in a few preexisting neurons can lead to behavioral diversification and, ultimately, contribute to species differentiation.
Dr. Yusuke Hara, co-lead author
Advanced ICT Research Institute
National Institute of Information and Communications Technology
Kobe, Hyogo, Japan.
We’ve shown how we can trace complex behaviors like nuptial gift-giving back to their genetic roots to understand how evolution creates entirely new strategies that help species survive and reproduce.
Dr. Daisuke Yamamoto , senior author
Advanced ICT Research Institute
National Institute of Information and Communications Technology
Kobe, Hyogo, Japan.
Publication:
AbstractOne of the central dogmas of creationism is that so-called “macro-evolution” is impossible because it would require “new genetic information” to appear from nowhere. Creationists insist that mutations can only corrupt existing information, never generate novelty
In accepting a courting male, Drosophila subobscura females require nuptial gift giving in which a male gives regurgitated crop contents to her mouth to mouth. No similar behavior is found in D. melanogaster. By clonal activation of neurons expressing the male-determinant FruM, we identified insulin-like peptide–producing cells (IPCs) and their putative postsynaptic targets, proboscis-innervating motoneurons, as those critical for gift giving. We demonstrate that loss of FruM from D. subobscura IPCs abrogates neurite extension and gift giving, whereas FruM overexpression in their D. melanogaster counterparts induces overgrowth of neurites that harbor functional synapses, culminating in increased regurgitation. We suggest that the acquisition of FruM expression by IPCs was a key event occurring in an ancestral D. subobscura that conferred a latent capability to perform nuptial gift giving.
But this experiment with fruit flies shows precisely how new behavioural traits can emerge without any supernatural intervention. The *fruitless* (*fru*) gene already exists in both species; the difference lies in how it is expressed and how it shapes neural wiring. A minor genetic variation lengthens a dendrite, connects two neurons that were previously unconnected, and produces a wholly new mating behaviour. In other words, new “information” is generated not by magic, but by natural processes acting on existing genetic material.
This finding also exposes the false distinction creationists try to draw between “micro-evolution” and “macro-evolution.” The shift in courtship behaviour isn’t trivial: it directly influences reproductive isolation, one of the key drivers of speciation. What creationists dismiss as impossible “macro-evolution” is demonstrated here in the lab—arising from the accumulation of small genetic changes with large evolutionary consequences.
Once again, science shows how species really diversify, while creationism offers nothing but denial. The fruit fly demonstrates that genetic variation, far from being limited to loss and decay, is the engine of evolutionary innovation.
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