Bigger beans- arriving in Italy and beyond

 An important contribution to evolutionary history, and breeding, of broad beans (Vicia faba) appeared in Vegetaion History and Archaeobotany recently, namely work by the Lecce archaeobotany laboratory on beans from southern Italy, by Grasso, Arthur and Fiorentino (2025). This study documents the appearance of two step changes in broad bean sizes in the Medieval period, backed up by measurement data on a small set of comparative land races, but only from Italy. This paper seems to miss the opportunity to think more broadly about the timing and processes of the evolutionism of gigantism in Vicia faba, which is just one of a group of pulses that evolved larger-seeded varieties in circum-Mediterranean agriculture- a pattern that Vavilov drew attention to under the heading "Regularities of type-forming processes" (Vavilov 1926). This provides an opprotunity to ponder what processes drove evolution of, and cultural preferences for, macro-seeded forms of pulses in this region but not in others, and it relates to the broader issue of the mechanisms that drive regional varietal evolution in crops, which can indicate remarkable parallel evolution across different crops in the same region.

While broad beans (Vicia faba) are among the Neolithic domesticates of the Near East, and part of the the Neolithic dispersal in Mediterranean Europe, the beans one is likely to be familiar with today-- at least in traditional agriculture in Europe, North Africa or Turkey, are generally quite different and much larger than those of prehistory. To be sure beans would have increased over the size of their wild progenitor (although the wild progenitor appears now to be extinct: see Kosterin 2015, Caracuta et al. 2016), but they were modest-sized cultivars, classed as variety minor. In Britain we typically refer to these as "Celtic breans", appearing in the Middle Bronze Age and becoming moderately common in southern England in Late Bronze Age and Iron Age times (as per the useful review of Treasure and Church 2017). In England such archaeological finds, charred, are consistenlty less than 8mm long, putting their uncharred dimeniosn likely under 1cm (assume -20% for charring). Although poorly undertsood some small-seed faba beans are also grown in part of the Indian Himalaya, referred to in the past as subsp. paucijuga, but with no real archaeobotanical indications yet of when they got there.

Larger beans in historical Italy

Somewhat larger beans in Southern Italy and Naples, that can be classed as variety equina, the "horsebean", appear as a minoriy of finds only in the late 7th century AD at the site of Colmitella (Grasso et al 2025). Such seeds have lengths consistely >1cm and typically near 1.5cm, and maximum widtth >1cm. After this equina types become more widespread in Southern Italy. By around this time equina type beans have also been reported from Panjakent in Uzbekistan, and although Grasso et al raises some questions about this, I would see this as also representing larger faba beans of the mid First MIllennium AD.

Even bigger beans, of variety major, with lengths around 2cm beginning to appear in Southern Italy in the 13th century. Grasso et al. argue that these steps of size increase may derive from breeding for larger beans, perhap in Southern Italy-- farmers selecting first for equina and then some centuries later for even larger major varieties. 

The overall conlusion of Grasso et al. is to emphasize the importance of archaeological seed measurments, as a tool to discern variation and evolution within crops over time, even long after domestication (when measurments are more commonly used and reported). This I fully concur with. However, I would raise some alternative hypotheses and unanswered questions about the drivers of seed size increase in Vicia faba, by noting that this is one among a group of peer species that have similar geographically restricted patterns of seed gigantism in the Mediterranean.

Mediterranean macrosperma pulses

As I already noted Vavilov drew attention to the occurrence of large seeded pulses in Mediterranean Europe and Turkey as a recurrent varietal feature.  This pattern is seen not just in Vicia faba, but also lentil (Lens culinaris), pea (Pisum sativum), chickpea (Cicer arietinum) and grasspea (Lathyrus sativus). The most stark contrast is between the small seed size and seed weight of varieties of these species found in India versus the larger sizes found in Spain and Italy. Smaller sizes also typically characterize these crops in Ethiopia, Afghanistan and Iran. Vavilov's data indicates that average seed dimeters of Italian lentils are two times those of India, with seed weights about 4 times greater. In chickpea, Indian types are typically ~30% shorter than those of Italy with as much of 70% less weight. Peas are about 50% lighter in India than Italy, and grasspeas too are also substantially smaller (Vavilov compares those from France, Ethiopia and India). Thus rather than seeing this as a product of targetted breeding of bigger beans by Medieval Italians, I think there is an issue of parallel evolution that demands explanation. The map at left/above from Muratova (1931), part of Vavilov's research team, shows that in the early 20th century large-seeded (major) faba beans are European and Mediterranean. Similarly the large seeded (macrosperma) varieties of lentil overlap this: the map of another part of Vavilov's team, Helena Barulina shows this (right/below). Grasspea, pea and chickpea similarly overlap. 

So what we have is a feature of geography and history that is influencing several crops in parallel. I would therefore suggest that instead of explaining this by intentional selective breeding we need to think about evolutionary factors, environmental and cultural, that might drive this. It would be nice to have comparable seed size data across all of these to look at species and see if the timing of stepped increases were similar. (In some of the cereals we do see linked regional patterns of change... but I'll leave that for another blog...see Dal Martello et al 2025). Perhaps, they might contend, in Italy (or elsewhere in the Mediterranean) breeders were targetting these pulses to select them bigger. (And if this is the case, is there a cultural factor to do with bean cooking methods than favours this?). But such a view has the implication that farmers in other parts of the world were somehow incapable of this, which I find this an unconvincing notion of European exceptionalism! 

Instead we might frame hypotheses about factors that favoured smaller seeds, for example in Afghanistan or India. Small seeds should require less water during the period of seed filling, and in crops such as this that mature in the months after winter that are hot and dry in places like India this could be adaptive. By contrast in the more gentle, showery spring around the Mediterranean water is not in such short supply. Smaller beans can be expected to cook faster too, so they might have lower wood fuel demands in areas where fuel is at a premium (across Iran and semi-arid India).  We can also think about other factors that promote larger seeds, such as increasing field disturbance and burial depth. It is only in the Mediterranean from late Roman times onwards that true ploughs, the mouldboard plouogh that turns over the soil, comes into use, whereas in India scratch ploughs (the ard) persist (even to today). I have previously speculated (Fuller 2007) that technological differences such as this might favour size increases under the deeper ploughing regimes. On top of this some farmer choice may well have operated too as an additional amplifier-- after all seed size multi-genic trait. 

I would note that there is another set of pulses and geographical context where gigantism can be noted, in East Asia. Here soybeans and adzuki beans also have macro-seed varieties much larger than the early domesticates that are well-documented in Neolithic or Bronze Age times. It also a part of the world were true ploughs that turn the soil come into use by the early centuries AD (Han Dynasty), spreading thereafter. Is this another context in which advances in tillage technology, perhaps coupled with irrigation and reduction of water stress, set in place conditions of seed gigantism to evolve in legumes. This seems to me to call for thinking about common causal drivers of unconscious selection that cut across cultures and crop species. Clearly more time series of archaeobotanical measurements are needed to make such comparative studies feasible.

Bibliography

Barulina, Helena (1930) Lentils of the U.S.S.R. and of other Countries. Bulletin of Applied Botany, of Genetics and Plant-Breeding 40. Leningrad [in Russian, with English summary]

Grasso, A. M., Arthur, P., & Fiorentino, G. (2025). Morphometrics shed new light on the first archaeobotanical evidence for the cultivation and breeding of Vicia faba var. equina (horse bean) and var. major (broad bean) in medieval southern Italy. Vegetation History and Archaeobotany, 34(6), 813-823.

Muratova, V. S. (1931) Common Beans (Vicia faba L.). Bulletin of Applied Botany, of Genetics and Plant-Breeding 50. Leningrad [in Russian, with English summary]

Vavilov, N. I. (1926) Centres of origin of cultivated plants. Bulletin of Applied Botany, of Genetics and Plant-Breeding  16(2) [Russian original], English Translation by Doris Love in Vaviliv (1992) Origin and Geography of Cultivated Plants. Cambridge University Press.