> ## Content Index > Fetch the complete content index at: https://modalpathethics.com/llms.txt > Use this file to discover other available public pages before exploring further. # Transition Action: The Brain Had Two Beginnings - URL: https://modalpathethics.com/transition-action-the-brain-had-two-beginnings/ - Published: 2026-09-21T11:00:22.000Z - Updated: 2026-09-21T17:01:33.000Z - Description: The controller was a relation before it was a throne. - Author: Aidan Lawson - Tags: Transition Action, Chastening of the Controller > ***Transition Action*** is the technical wing of Modal Path Ethics: a series about technologies crossing from research, prototype, or theory into reachable action. Each entry begins with a live technical event and asks what has changed in the field. This is not a futurist roundup. - What can now be built, tested, measured, or operationalized that was not reachable before? - What physical process carries the new action? - Which old background assumption has become less necessary? > ***Transition Action* is a field inspection at the moment a capability starts to move.** --- This week in *Transition Action*, the brain has been caught playing *Chirality*. ![](https://storage.ghost.io/c/20/43/2043f11a-6ae3-404c-bb28-01fce8d9ac88/content/images/2026/09/image-177.png) Dundes et al., bioRxiv (2025), CC BY 4.0. A paper published in *Nature Neuroscience* reports evidence against one of the cleaner stories about how the vertebrate brain begins. The clean story goes like this. - Early neural tissue appears. - One broad progenitor population gives rise to **the brain**. - Regional signals divide the developing structure into *forebrain*, *midbrain*, and *hindbrain*. - Eventually somebody acquires a mortgage and begins worrying about YouTube drama. The new story begins with a split. Rayyan Jokhai, Carolyn Dundes and collaborators used lineage tracing in mouse embryos and differentiation experiments with human pluripotent stem cells to support the existence of **two parallel neural ectoderm progenitors during gastrulation**. One is anterior. - **Anterior neural ectoderm** - → forebrain - → midbrain The other is posterior. - **Posterior neural ectoderm** - → hindbrain These populations do not arrive as identical neural material waiting for later instructions. They already carry different developmental competencies. They already show different accessible-chromatin landscapes. They already possess different reachable futures. The authors call the brain a **composite organ** arising from two lineage-restricted progenitors. New Scientist looked at this one and immediately went with: > ***OUR BRAIN EVOLVED FROM TWO PRIMITIVE NERVOUS SYSTEMS THAT MERGED.*** Modal Path Ethics would like everyone to remain calm. For about three paragraphs. Then we are **absolutely** going to make this even worse. --- ## Do Not Invent Two People. First, the emergency brake. This paper does not show that you contain two consciousnesses. It does not establish two selves. This has nothing to do with the popular **left-brain/right-brain** mythology. The split is not between the cerebral hemispheres. It does not show one brain region quietly resenting another brain region for receiving more funding. The developmental distinction is anterior neural ectoderm giving rise to the forebrain and midbrain, versus posterior neural ectoderm giving rise to the hindbrain. The authors' evolutionary interpretation also deserves its modal verb. They propose that the dual developmental origin ***may*** reflect a very ancient division, potentially conserved across roughly 550 million years from hemichordates to mammals. They found corresponding anterior and posterior populations across several species, including mouse, macaque, chicken, zebrafish, and an acorn worm lineage. That is very good evidence for an ancient developmental split. It does not let us watch two Precambrian nervous systems crawl toward one another and shake hands. Nature's own coverage notes disagreement over the strongest version of the conclusion that the brain descends from two populations that remain developmentally distinct. Leave the disagreement alive. This paper is already strange enough. > **One mature brain can arise through two different developmental histories.** We do not need to add another brain. --- ## The Paths Are Different Before the Destination Exists. This is the important part. > A progenitor population is defined partly by what it can still become. That sounds *dangerously* familiar. The researchers generated anterior and posterior neural ectoderm-like cells from human pluripotent stem cells and then challenged them with signals intended to produce different brain-region identities. If the old picture were sufficiently permissive, these early cells might behave like relatively interchangeable neural starting material whose later destination depended mostly on the regional instructions arriving afterward. They did not. The anterior and posterior populations behaved as though important parts of their futures had already diverged. - The anterior population preferentially carried forebrain and midbrain potential. - The posterior population preferentially carried hindbrain potential. Their chromatin landscapes had already begun organizing around those different destinations before mature neurons appeared. This changes the question from just: > What instruction should this cell receive? There is now another question before it. > **Which developmental path is this cell *already on*?** The distinction is viciously important. The same instruction does not necessarily mean the same thing everywhere. The same signal does not necessarily open the same future from every state. A **path** changes what later commands can still accomplish. *Chirality* has escaped yet again. --- ## The Board Has Entered the Embryo. Modal Path Ethics built [*Chirality*](https://modalpathethics.com/chirality/) around a very annoying rule. > The arrangement of the board matters. A piece cannot be understood independently of where it stands. Board geometry participates in determining what the piece can do, where it can move, what it threatens, and which later routes remain reachable. Then laboratories started doing this to us. [Transition Action: Chirality Has EscapedArrangement gives light a hand. Strain gives matter a hand. Chirality is a move now. A special edition.![](https://storage.ghost.io/c/20/43/2043f11a-6ae3-404c-bb28-01fce8d9ac88/content/images/icon/thin-tile.rulebook-2-cb295d35-d48a-4d39-b59c-72e70db3b43a.png)Modal Path EthicsAidan Lawson![](https://storage.ghost.io/c/20/43/2043f11a-6ae3-404c-bb28-01fce8d9ac88/content/images/thumbnail/Screenshot-2026-07-31-064637-4026fe61-da8a-4fbf-a64a-e151609e299a.png)](https://modalpathethics.com/transition-action-chirality-has-escaped/) In *Transition Action: Chirality Has Escaped*, locally achiral circular holes were arranged into an aperiodic structure that produced chiral optical behavior. No individual hole contained the handedness attributed to the larger field. The relation carried something the component did not possess alone. The article's central correction was simple: > **Structure is part of the action.** The world is not passive terrain underneath the actor. The field participates. Neurodevelopment is obviously not nanophotonics. Anterior neural ectoderm is not a Thicktile. **Nobody** should place the gastrulating embryo inside the *Chirality* rulebook. The shared lesson sits one level higher. > **A component's reachable identity can depend on the structured path in which it occurs.** The researchers did not discover two differently colored piles of generic neural matter. They found populations whose histories already constrain what later transformations can reliably produce. That is the board entering the piece. The same move does not mean the same thing everywhere. Development has position. Development has history. Development has **reachability**. --- ## Unfortunately, The Controller Is Back. This creates a problem for a completely different Modal Path Ethics department. The [**Chastening of the Controller**](https://modalpathethics.com/tag/chastening-of-the-controller/) began with machines. [*Transition Action: Shape Is Already Code*](https://modalpathethics.com/transition-action-shape-is-already-code/) looked at physical computing and soft robotics and found computation leaking into bodies, materials, geometry, and mechanics. The controller was losing its monopoly. Then a cyborg cockroach arrived wearing scuba equipment. [Transition Action: The Animal Becomes the ActuatorHumanity has begun issuing diving gear to cockroaches. This is not a drill.![](https://storage.ghost.io/c/20/43/2043f11a-6ae3-404c-bb28-01fce8d9ac88/content/images/icon/thin-tile.rulebook-2-688ebd10-ab2e-49bc-bc57-f82b4362f4ab.png)Modal Path EthicsAidan Lawson![](https://storage.ghost.io/c/20/43/2043f11a-6ae3-404c-bb28-01fce8d9ac88/content/images/thumbnail/Screenshot-2026-06-29-175957-59077b8c-7342-43b7-830f-e2037a5f5a08.png)](https://modalpathethics.com/transition-action-the-animal-becomes-the-actuator/) That article found an amphibious robotic capability distributed across insect muscle, electrical stimulation, oxygen chemistry, a flexible shell, respiratory interfaces, center of gravity, water resistance, and host metabolism. Control did not sit in one clean box. Then [*The Signal Never Becomes Data*](https://modalpathethics.com/transition-action-the-signal-never-becomes-data/) became openly disrespectful. A soft mechanical sensor could route physical contact directly into fluidic actuation without first translating the event through a powered electronic controller. Some control lived in software. Some lived in geometry. Some lived in material compliance. Some lived in fluid routing. Some lived in the environment supplying the force. The article finally revoked the controller's imperial title: > **No single box gets to impersonate the whole machine.** > Controller chastened. Everyone go home. The brain has now reopened the investigation. Because the obvious place to hide the controller is the brain. The body does local computation. The environment participates. Materials answer before representation. But surely, **somewhere** upstream, there remains one sufficiently respectable object where the intelligence finally lives. We have a word for it. > **Brain.** There. See? Found the controller. The new developmental evidence asks an extremely inconvenient question. > Where did that object come from? --- ## The Controller Had to Be Built. Before there was a forebrain coordinating higher-order behavior and before the hindbrain was carrying life-sustaining functions, there was no completed brain available to supervise its own construction. - There were developmental processes. - There were signals. - There were gene-regulatory states. - There were tissues occupying positions in an embryo. - There were cells taking up those signals differently. - There were anterior and posterior neural ectoderm populations entering different developmental trajectories. Eventually those trajectories became integrated strongly enough that we could point at the mature structure and give it one excellent noun. > **Brain.** That noun is useful. It is also late. This is the Chastening of the Controller from behind. Previous entries kept finding causal work outside the controller. **This** one catches the controller before it exists. No little brain stands above gastrulation issuing instructions for brain production. The thing that will later coordinate the organism has to emerge from coordination first. That is a much deeper humiliation. > **Before the controller could control anything, its own conditions had to coordinate.** --- ## Please Return the Brain. There is an equally bad mistake available from the other direction. If the brain decomposes into developmental histories, tissues, signals, cell populations, genetic regulation, metabolism, body, environment, and all the other relations needed to produce and maintain it, **perhaps the brain was never really an object at all.** Congratulations. You have performed the **Relational Descent** so aggressively that the patient has disappeared. Modal Path Ethics recently encountered exactly this problem. [*Hoel and the Causal Locus*](https://modalpathethics.com/hoel-and-the-causal-locus/) began after the framework noticed that intelligence, institutions, selves, and other noun-shaped objects kept dissolving into relations whenever inspected closely. Erik Hoel's work on causal emergence supplied an important correction. A higher-order pattern can be completely constituted through lower-order processes while retaining causally meaningful organization at its own scale. Decomposition does not automatically make the higher-order locus fictitious. > Relations can constitute objects. Then [Simondon](https://modalpathethics.com/simondon-and-the-locus-in-formation/) made the whole situation worse again. If the individual is relationally constituted, we should not always begin with completed individuals and treat their relations as secondary. Sometimes the interesting question is: > **How did these relations become this individual?** The brain paper has walked directly into that argument. The mature brain is real enough to sustain injury, memory, regulation, perception, learning, action, development, disease, and repair. Its developmental composition does not dissolve it. It gives us a history of how that locus became available. The two paths do not abolish the brain. They help constitute it. --- ## A Candidate Causal Dyad? Now we can use the dangerous phrase. ***Very carefully.*** The paper supports a **developmental dyad** more directly than a *causal dyad*. Two lineage-restricted neural ectoderm populations emerge in parallel and contribute to different major regions of the later brain. That alone does not establish that the anterior-derived and posterior-derived systems form a distinct higher-order causal unit in the technical sense Modal Path Ethics has recently been exploring. To earn that stronger claim, the relation itself has to do causal work worth describing at that scale. Intervene here. Perturb there. Break the coupling. Alter timing. Change the interface. Then ask whether the resulting transition structure is better captured through the relation between the differentiated systems than through either one considered alone. That experiment has not been performed by this paper. So do not promote the developmental result beyond its jurisdiction. Still, look at the candidate. - Two distinct developmental trajectories. - Different competencies. - Different chromatin organization. - Different downstream regions. - Later physical and functional integration. - One continuing organ. That is exactly the kind of structure for which a causal-locus analysis becomes interesting. The brain may turn out to contain many relevant causal decompositions. Of course it does. There is more than one relevant grain of analysis. The claim here is narrower. > **One of nature's paradigmatic apparent controllers now arrives with evidence of a deep dyadic developmental history.** That is enough to put the causal question up on the board. --- ## **Good Fucking Luck** Finding the Isolated Self, By the Way. This is where everyone should behave themselves. - We are not deriving a theory of personal identity from embryology. - We are **also** not going to pretend this has no philosophical pressure because [philosophy becomes embarrassed whenever a microscope enters the building](https://modalpathethics.com/the-categories-cannot-hold/). Consider the ordinary intuition. > There is a person. Inside that person is a brain. Inside that brain is where the **real internal business** happens. That picture encourages a peculiar metaphysics in which relation looks secondary. - The object comes first. - Then it interacts. Now descend. ![](https://storage.ghost.io/c/20/43/2043f11a-6ae3-404c-bb28-01fce8d9ac88/content/images/2026/09/image-178.png) The brain's apparent unity reaches backward into two developmental lineages. Descend into either lineage and find different signaling pathways, transcription factors, chromatin accessibility, neighboring tissue, timing, geometry, metabolism, inherited molecular machinery, and the environment through which those processes acquire consequence. Nothing in that descent requires declaring the person unreal. It does make the isolated object much harder to find. The closer we get, the more the thing's history seems to consist in **structured relations that became stable enough to earn a boundary**. Modal Path Ethics has spent months doing just this. - Intelligencebecame relational. - Controlbecame relational. - Institutional knowledge became relational. - Causal loci came back as organized relations. - Simondon moved individuation before the completed individual. - Chirality kept appearing where arrangement carried behavior no isolated component possessed. Now the brain has joined the pile. **Good fucking luck** finding the isolated self in there. It seems relations got here first. --- ## The Useful Part. Modal Path Ethics should now return from philosophy before the developmental biologists confiscate all our equipment. The researchers did not stop at discovering an interesting embryonic division. They went right ahead and used it. This is the reason the paper belongs in ***Transition Action***. - Generating human forebrain and midbrain cell types from pluripotent stem cells has become comparatively tractable. - Hindbrain populations have been harder. - The new work suggests one reason. Researchers may have been attempting to reach some hindbrain fates after beginning from a developmental state whose competence was already wrong for the trip. Jokhai, Dundes and colleagues instead differentiated human pluripotent stem cells into posterior neural ectoderm and used that route to produce rhombomere 5/6-specific hindbrain motor neurons that had previously been difficult to generate in vitro. Those neurons included molecular hallmarks of the relevant hindbrain identity and showed electrophysiological activity. There it is. > *The ontology did work.* Not philosophical work. > **Laboratory work.** **Recognizing the path** changed what the researchers could make. > **The signal was not enough.** > **The starting relation mattered.** Or, in Modal Path Ethical terms: > **Developmental competence is reachability with a body.** If a cell's path history has already altered which transitions remain available, a later command cannot be evaluated independently of the state receiving it. The intervention has to meet the locus that actually exists. That is *Transition Action* territory. --- ## What This Makes Reachable. The immediate reachability is narrow and real. - Human pluripotent stem cells can be differentiated into anterior and posterior neural ectoderm-like populations representing different early developmental routes. - Those populations can be compared through transcriptional and chromatin-level differences. - Posterior neural ectoderm supplies a route toward hindbrain-specific progenitors and neurons that have been difficult to generate cleanly in vitro. - Rhombomere 5/6-specific motor neurons become more experimentally accessible. - Researchers gain a better platform for investigating hindbrain development and disorders involving cells from those regions. The longer reachability is more interesting. > Researchers can now ask whether disorders associated with different brain regions begin partly in the divergent developmental paths that precede those regions. > They can test when anterior and posterior competence becomes established. > They can perturb the interface. > They can examine how two early developmental programs become one integrated organ. > They can ask which features remain lineage-specific and which become properties of the coupled brain. > They can improve region-specific neural models without assuming that every desired neuron sits downstream from one interchangeable neural starting state. And, eventually, somebody can run the experiment Modal Path Ethics now wants **very** badly: > **At what scale does the relation between these developmentally distinct systems become a causally informative object in its own right?** That experiment is just *waiting* out there. Modal Path Ethics will try not to publish its result in advance. --- ## The *Transition Action*. The official Transition Action is to **move brain-region identity earlier in the path**. The old developmental picture left more of the brain's regional future available to later specification from a broadly common neural progenitor. The new evidence places a major bifurcation during gastrulation. - Two neural ectoderm populations emerge. - Their chromatin begins diverging. - Their developmental competencies diverge. - One path carries forebrain and midbrain futures. - The other carries hindbrain futures. The distinction is early enough to change how human stem cells should be routed if the desired destination is a specific hindbrain neuron. That makes the transition experimentally consequential. - **Do not begin with “neural.”** - Ask which neural path. - **Do not treat the later region as a label added to interchangeable material.** - Preserve the developmental route capable of reaching it. - **Do not assume the mature organ tells you where its unity began.** - Follow the histories that had to meet. The brain did not begin as one little controller waiting to acquire components. It arrived through differentiated continuations that eventually became capable of carrying one another inside the same organ. - Anterior path. - Posterior path. - Different competence. - Different history. - Different futures. - Then connection. - Then integration. - Then: - **brain.** > The controller was a relation before it was a throne.