LessWrong (Curated & Popular)
"No, we haven’t uploaded a fly yet" by Ariel Zeleznikow-Johnston
21 Mar 2026
Transcript generated automatically by AI and may contain errors.
Chapter 1: What recent claims have been made about uploading a fruit fly?
No, we haven't uploaded a fly yet. By Ariel Zalesnikow-Johnston. Published on March 19, 2026. In the last two weeks, social media was set abuzz by claims that scientists had succeeded in uploading a fruit fly. It started with a video released by the startup Eon Systems, a company that wants to create brain emulation so humans can flourish in a world with superintelligence.
On the left of the video, a virtual fly walks around in a sampit looking for pieces of banana to eat, occasionally pausing to groom itself along the way. On the right is a dancing constellation of dots resembling the fruit fly brain, set above the captioned simultaneous brain emulation. At first glance, this appears astounding, a digitally recreated animal living its life inside a computer.
Chapter 2: What is the significance of Eon Systems in brain emulation?
And indeed, this impression was seemingly confirmed when, a couple of days after the video's initial release on X by co-founder Alex Wisnergross, Eon CEO Michael Andreg explicitly posted, we've uploaded a fruit fly. There's an image here. Description.
Michael Andreg tweets, We've uploaded a fruit fly. We took the at Flywire News connectome of the fruit fly brain, applied a simple neuron model, at philip underscore shoe nature 2024, and used it to control a MuJoCo physics simulated body, closing the loop from neural activation to action. A few things I want to say about what this means, and where we're going at at Ian's East. bar chart.
Video shows a close-up 3D-rendered fruit fly with labeled parts Proboscis and Sue pointing to different anatomical features, displaying 042 duration.
Yet extraordinary claims require extraordinary evidence, not just cool visuals, as one neuroscientist put it in response to Andregg's post. If Eon had indeed succeeded in uploading a fly, a goal previously thought to be likely decades away according to much of the fly neuroscience community, they'd need more than a video to prove it.
Did the upload show evidence of known neurophysiological markers of working memory, such as the head direction ring attractor bump? How did their brain model actually control the virtual fly body, given it seemed to lack a modelled spinal cord? Where was the data and the write-up?
Because if E.ON couldn't back up what their video seemed to show, at least some neuroscientists were going to be markedly less than impressed. There's an image here.
Michael Andreg tweets, Thank you to the neuroscience community. We're standing on the shoulders of giants. Especially Janelia. At Flywire News. At Srinagaraga et al. At Neuromechfleet. Less than three also thanks to our advisors at Robin Hansen. at GeoChurch, Stephen Larson, at Courting Lab, at Anders Sandberg, Ken Hayworth, and many.
Kenneth Hayworth replies, Private Advisor and my most important unheeded, advice was not to declare that you uploaded a fly unless you had damn good evidence, because otherwise you would piss off the Drosophila research community. I take uploading seriously, so please point me to the publication.
Eon did follow up with a blog post, how the Eon team produced a virtual embodied fly, detailing how they combined pre-existing models of the fly brain and body into a system that could respond to virtual environmental cues.
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Chapter 3: What evidence is needed to support the claim of uploading a fly?
Nobody says I've partially uploaded this photo to mean I've made a rough sketch inspired by it. An uploaded fly, then, should be able to do everything the original fly could do. It should be playable forward in time indefinitely, responding to novel situations as the original would have. It should serve as a faithful proxy for the real thing.
So much so that a neuroscientist could peer inside, observe realistic equivalents of neurophysiology, and run experiments that would be impractical or impossible on a biological fly, with confidence that the results would generalize back. The leading proposal for how to actually achieve this is whole-brain emulation.
Faithfully recreating the brain's causal mechanisms at whatever level of detail turns out to be necessary so that the digital system behaves identically to the original. This is what distinguishes emulation from simulation.
A weather simulation is useful, it can predict next week's temperature with reasonable accuracy, but it breaks down when pushed further out because its approximations are coarser than the actual atmospheric processes of real weather.
Chapter 4: How has the neuroscience community reacted to Eon's claims?
In contrast, one can run an emulation of the Nintendo 64 game Banjo-Kazooie on a laptop, and because the emulator faithfully recreates the logic of the N64's hardware, the processor, the memory, the graphics pipeline, the game will never fail to behave as it would have on the original console.
It's currently an open scientific question what level of biological detail an emulation needs to capture. It's unlikely we'd need to simulate every ion channel, and perhaps much of the brain's physiology could be simplified with no consequence. But the key feature of the emulation approach is the guarantee.
If you've faithfully recreated the causal mechanisms down to the necessary level, the resulting behavior is trustworthy by construction. Low-fidelity approaches might produce correct-looking behavior in some cases, but it's hard to tell to what degree this will generalize to novel situations.
In response to this line of criticism, Michael Andreg has argued that uploading shouldn't be considered so binary. I don't think of uploading as a binary concept, he told The Verge, outlining the different levels of upload. By this logic then, Eon's system, containing connectome-derived elements driving behavior in a virtual body, might qualify as a partial upload.
But if a connectome-constrained model can count as a partial upload, then the Shu et al. brain model was already a partial upload before Eon touched it. So was the Lapelainen visual model. So, for that matter, is any computational neuroscience model that incorporates anatomical connectivity data.
The word uploader loses its distinctive meaning, and the field loses its ability to communicate what it is actually trying to achieve and how far away a true fly upload still is. Heading. Still loading. When the vocabulary of breakthroughs is spent on incremental demos, the actual breakthroughs are cheapened when they arrive.
Funders and the public lose the ability to distinguish genuine milestones from slick demos, and investment flows towards groups making the boldest claims rather than those doing the most foundational work.
Worse, for a field that is struggling to graduate from science fiction to serious research, premature claims risk triggering the cycle of hype and disillusionment that has set back other ambitious programs before. To be fair, we're not unsympathetic to why E.ON used the language they did.
Their careful blog post on how the Eon team produced a virtual embodied fly would likely have only been read by a few hundred neuroscientists, whilst we've uploaded a fruit fly reached millions. Startup survival requires investment, funding follows excitement, and excitement follows headlines, not careful caveats.
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