What carries the argument is a covariance across species, not a wiring diagram traced from a lizard to a person. Look at any single limbic structure and you get an idiosyncratic story about smell, or navigation, or memory [12]. Look at them as a set and they rise and fall together, in the opposite direction to the neocortex [8], which is why Nabil Imam describes coordinated expansion rather than independent drift [9].
The proposed cause is a budget. Cortical circuits are laid out as spatial maps: the patch handling the thumb sits beside the patch handling the index finger, and the systems for sight and sound are arranged the same way [11]. Limbic circuits are not built like that. A particular smell or a complex memory is carried by a distributed pattern, closer to a bar code than to a map [13]. Both schemes, on Imam's account, are in place before birth [7], and if both are specified in advance out of the same finite space, more of one means less of the other. That is the shape the comparative data has [6].
The 70 years in the Georgia Tech headline [22] survive checking. The layered model was proposed in the 1950s [4] and the release is dated August 31, 2026 [1], which puts about 71 years between them [18].
The thing this doesn't tell you is anything about the argument you had with yourself yesterday. The popular reason-against-instinct picture is a claim about two systems competing inside one head [20]; this is a measurement of relative region size between species [8]. A trade-off in how brains get built does not license a claim about how a brain decides, and the work as summarised does not make one.
The summary also does not say how the artificial networks came out [21]. That gap matters more than it looks. The innateness result is what would turn a correlation between region sizes into a claim about connectivity that has to be committed early, before experience can shape it. Until those numbers are visible, the anatomy stands on its own and the tug of war is the interpretation hung on it. My view, with that condition attached: the comparative pattern is the durable half, and it is already enough to stop treating the limbic system as an older brain that a newer one sits on top of [5].
