Jared Diamond’s famous argument in Guns, Germs, and Steel is seductively simple: Eurasia had an east-west axis, so crops, animals, tools, and ideas could move across similar latitudes more easily than in Africa or the Americas, whose north-south axes forced innovations through sharper climate gradients. In short, geography gave Eurasia a head start.
The article “Geography is not destiny: A quantitative test of Diamond’s axis of orientation hypothesis” (https://pubmed.ncbi.nlm.nih.gov/38274321/) asks a beautifully direct question: is that actually true?
The answer is nuanced. Ecology does seem to shape cultural transmission. But Eurasia does not appear to have enjoyed the sweeping ecological advantage Diamond’s argument requires.
What The Article Tests
The paper breaks Diamond’s idea into two separate claims.
First: societies in similar environments should be more likely to share cultural traits.
Second: Eurasia should contain especially smooth ecological corridors, allowing agriculture and other innovations to spread more easily than in other continents.
The authors test the first claim using cultural data from D-PLACE, covering 1,094 mainland traditional societies and 67 cultural traits. They compare pairs of societies and ask whether they are more likely to share traits when they are closer in temperature, aridity, topography, and travel cost.
They test the second claim using known centers of agricultural origin. If Diamond is right, then ecological barriers outward from Eurasian agricultural centers, especially the Fertile Crescent, should be consistently lower than barriers around agricultural centers in Africa or the Americas.
The Main Result
The first half of Diamond’s intuition survives.
Environmental barriers do matter. Societies separated by greater temperature differences, aridity differences, difficult terrain, or high travel costs are generally less likely to share cultural traits. This is especially true for traits tied closely to ecology, such as subsistence, housing, crops, domestic animals, and settlement patterns.
But the bigger historical claim does not survive cleanly.
Eurasia is not consistently more ecologically homogeneous than other regions. The Fertile Crescent, in particular, is not simply an easy launchpad into a smooth east-west ecological highway. It is river-fed, but surrounded by deserts, elevation changes, and strong aridity gradients. So the geography is more complicated than the map-outline version of Diamond’s story suggests.
Methodological Strengths
The best part of the article is that it does not attack Diamond with anecdotes. It operationalizes the hypothesis.
Instead of saying “Eurasia looks east-west,” the authors ask: what are the actual ecological costs along plausible routes of cultural movement?
That is a strong move. They measure not only straight-line distance, but also least-cost paths through climate and topography. They also control for common ancestry using language phylogenies, and for possible cultural borrowing from nearby societies. This matters because two societies may resemble each other not because one copied the other directly, but because both inherited traits from a common ancestor or because both were influenced by a local cultural neighborhood.
The authors also avoid treating “culture” as one thing. They test many cultural traits separately, which reveals a more interesting pattern: ecology matters for some traits much more than others.
Methodological Weaknesses
The biggest limitation is temporal mismatch.
Many cultural data points come from ethnographic records of relatively recent societies. But Diamond’s argument is mainly about deep historical processes, especially the Neolithic spread of agriculture. Present or recent cultural similarity is not the same thing as ancient innovation transmission.
The authors know this and partially address it. For the agricultural-origin analysis, they repeat the climate analysis using reconstructed climates at 12,000, 8,000, and 4,000 years ago. That is a good sensitivity test. But it still remains coarse. Agriculture did not spread everywhere at the same time, and different crops had different ecological windows. A region-specific time model would be stronger than three global snapshots.
Another limitation is that cultural traits can travel in bundles. If agriculture spreads along with settlement patterns, property norms, and political hierarchy, then several “independent” cultural traits may partly reflect one larger package. The authors mention this, but it remains a real interpretive challenge.
Should Climate Be Present-Day Or Past Climate?
For testing recent or historically documented cultural similarity, present-day or long-term recent climate is acceptable as a rough ecological proxy.
But for Diamond’s core claim about agriculture and early state formation, climate should not mainly be present-day. It should be paleoclimate.
The most relevant window is the early-to-middle Holocene, roughly 12,000 to 4,000 years ago. If I had to pick one broad midpoint, I would use around 8,000 years ago, because it sits near the period when agriculture was spreading in several regions. But the best approach is not one date. The best approach is time-sliced and region-specific:
- 12 kya for earliest post-glacial ecological conditions and early domestication contexts
- 8 kya for major early agricultural expansions
- 4 kya for later consolidation and wider spread
So the article is right to include 12, 8, and 4 kya. The remaining weakness is that these are broad snapshots, not crop-specific or route-specific historical reconstructions.
Is The Article Silently Pushing A Genetic Explanation?
No. If anything, it pushes against genetic determinism.
The article’s central message is anti-deterministic: geography is not destiny, and neither are ecology or genetics. It does use language phylogeny as a proxy for shared cultural ancestry, and that language tree incorporates some evidence about human population history. But that is not the same as claiming genetic superiority or genetic causation.
The authors are controlling for inherited cultural relatedness, not arguing that populations differ because of innate biological differences. Their conclusion explicitly warns against single-factor explanations. The paper is not replacing geography with genetics. It is saying that human history is too complex for any one master key.
Final Take
This is a valuable article because it treats a famous grand theory with the right mix of respect and suspicion. It confirms Diamond’s smaller ecological intuition: environments can make cultural transmission easier or harder. But it rejects the stronger continental story: Eurasia was not obviously blessed with uniquely smooth ecological corridors.
The best takeaway is not “Diamond was completely wrong.” It is sharper than that: Diamond identified a real mechanism, but overextended it into a continental destiny narrative. The mechanism exists. The grand conclusion does not follow.
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