**Built a global geological index from plate-boundary density, aridity, and river proximity. The top 2% of cells is mostly where you'd expect — and also where four primary civilizations sit.**

Index is GCI = T × A × V on a 1° grid (15,351 land cells):

* **T**: distance-weighted plate-boundary density within 500 km, using Bird (2003)
* **A**: arid fraction from Global Aridity Index v3.1
* **V**: linear decay to nearest major river (Natural Earth scalerank ≤4)

Multiplicative on purpose. I'm specifically operationalizing desert-river circumscription (Carneiro 1970, extended to tectonics by Force 2008), not circumscription in general. Cells missing any component score zero by construction.

The high-GCI field clusters along the Alpine-Himalayan belt and the Andean margin (circum-Pacific, distinct regime, not a continuation). Moran's I ≈ 0.89, which is expected since topography is contiguous by physics, and which also means effective sample size for any cell-independence null is much smaller than 15,351.

The civilization angle is what I was testing for, and I'll flag it because it's why I built this - Egypt 98.9th percentile, Mesopotamia 99.5th, Indus 100.0th, Caral-Supe 93.6th. 

But the part I want geology pushback on is upstream of that: **is T × A × V a defensible operationalization of the Carneiro–Force chain (plate convergence → orogeny → rain shadows → desert margins → rivers cutting through), or am I collapsing things that shouldn't be collapsed?**

Specific concerns I already have:

* 500 km radius on T is broad. I'm using it as a proxy for regional orogenic crumpling, not anything a person could see. Defensible or too coarse?
* A uses modern (Holocene-recent) climate. African Humid Period (\~11–5 ka) means Saharan boundaries were materially different during/just before the formation period of three of these cases. Paleoclimate-adjusted version is next, but I want to know if there's prior work I should be reading first.
* Multiplicative composite is theoretically motivated but statistically aggressive. Open to argument that an additive or min-based composite would be more honest.

Code, data, Monte Carlo battery all on Zenodo. Paper under peer review. Looking for methodology pushback specifically, not the cultural-evolution stuff downstream.

Built a global geological index from plate-boundary density, aridity, and river proximity. The top 2% of cells is mostly where you'd expect, and also where four primary civilizations sit.