During the height of the Roman Empire there was a NW-SE (of course mostly west to east) gradient in per capita income. This is well known. One of the reasons given for the collapse of the Western Empire in the 5h century in contrast to the persistence of the Eastern Empire is that the provinces of the latter were wealthier and so could afford initiatives such as bribing barbarian tribes to move on toward the west. In Contours of the World Economy 1-2030 AD Angus Maddison confirms this (table below the fold). Additionally, in Peter Heather’s The Fall of the Roman Empire the argument is also made that expansion beyond the Rhine did not occur mostly because of the poverty of the lands; the lack of tax base meaning that the conquest wouldn’t have been self-supporting. So as you go north there is an inversion of the east-west wealth gradient. The main exception to this clinal geographic distribution of wealth is Italy, for obvious reasons. But there are a few other data which Maddison alludes to which interest me in relation to per capita income. He confirms that Germans were larger and more physically robust because they had more meat and milk in their diet (better sources of protein). Maddison also notes that Roman culinary science which reflected the needs and interests of the elites had a strong focus on condiments and sauces because even imported foods tended to go bad. I know that the Dutch became wealthy in the early modern period in part by exporting salted herring, but these data seem to imply that the Roman trade in food was mostly in grain. Unless curred or salted it seems that vegetables and meats wouldn’t make it. If there had been magic preservatives perhaps those in the wealthier provinces would have purchased milk & meat to shore up their nutritional intake? But decomposition constrained the possibilities for trade across long distances in such perishable food stuffs.
I bring this up because in Farewell to Alms Greg Clark used the distribution of lactose tolerance to imply that northern Europe had always been very wealthy, since after all milk was produced from cows which indicated a relatively high standard of living where land could be given over to husbandry. Now, Clark is obviously a smart guy, smart enough that Brad DeLong seems to have creamed himself with praise over his book, but that sort of assertion seemed really dumb and reinforces the perception that economists don’t know jack. After all, we have a good idea of the distribution of lactose tolerance and the nature of its evolution, and it seems that ecological constraints and possibly path dependence is very critical in conditioning whether this trait will emerge. In fact, as I note above scholars of the Roman period assume that the lands of Germany were relatively sparsely populated and poor if material data are any evidence (Hitler was irritated with Himmler for funding archaeological digs in Germany and Scandinavia because he felt it just made the ancestors look primitive). Gaul was wealthier and more densely populated. That serves to explain why it remained occupied after being gutted for the glory of Julius Caesar, while the campaigns of Germanicus served mainly to buttress the popularity of his insane son the emperor Gaius (Caligula).
Reading economic history I notice all sorts of glosses and oversimplifications when it comes to cultural details. I don’t mind that too much; I don’t read Maddison’s work for his analysis or even his often tenuous causal claims, but rather for his copious data sets. Nevertheless, when it comes to something like inferring economic conditions from biological data one can work out objections from the armchair without reading historical works. The extrapolation does though require taking non-economic dynamics and conditions seriously, which Clark presumably does.
Note: The estimates below are for 14 AD.