Post-Domestication regional evolution

Setaria italica grain variation:
above, from Gansu;
below, from Karnataka

It is true that evolution never stops--a suitable point to reflect upon on Darwin's birthday (12 Feb 1809) Some authors, would therefore insist, that domestication processes never cease and are always unfolding (a key argument in the recent book by Robert Spengler, Nature's Greatest Success), but I think there are grounds for differentiating the initial domestication episode that separates cultivars from the their wild population and later diversification and regional adaptation that took place within geographical subsets of a crop. In a paper in 2009, "The nature of selection during plant domestication", we drew attention to some differences and different expectations between domestication and diversification [incidentally that paper was also published in February 12, the 200th birthday or Charles Darwin]. The expectations are that diversification may occur over shorter timescales, differ between regions, and may (but may not) involve some conscious selection, based on farmer preferences. As archaeobotanical datasets have become larger and from more regions it offers the potential to compare and contrast how crops were evolving and differentiating across regions-- at least in those traits we can observe on archaeobotanical material. As noted in a recent blog (Bigger Beans...) there is clear evidence for selection for larger seeded legume crops around the greater Mediterranean some time after the classical period. While Grasso et al. (2025) argue for intentional selection in southern Italian farmers of the Middle Ages for larger broadbeans, I suggested in a previous blog that this might not be so because of the striking parallels across lentil, chickpea, grasspea and broadbean for macro-seeded forms around a wider Mediterranean world. This coincidence suggests to me an unconscious process of parallel evolution/adaptation to something in the ecology of bean farming in Late Antiquity to the Middle Ages (perhaps heavier tillage and also less incidence of water stress).

Aspects of grain size and grain shape are easily measured, and indeed have been measured for many years. Last year, in a large compilation of grain metrical data from archaeological assemblages acorss Eurasia, together with Rita Dal Martello, Robert Spengler and other colleagues from the Max Planck archaeobotany lab, we considered Contrasting diachronic regional trends in cereal grain evolution across Eurasia: a metadata analysis of linear morphometrics from the ninth millennium BCE to today. This study considered barley, free-threshing wheat (presumablty predominantly hexaploid bread wheat), and the millets of Chinese origin, Panicum miliaceum and Setaria italica. All four of these crops have pan Eurasain distributions, with dispersals beyond their regions of origin beginning in the Neolithic and having largely reached their maximum distributions by the end of the Bronze Age. As these crops came into a region one can expect them to adapt to local conditions, both ecological and cultural. What we found that is most striking, however,  is parallel trends in size/shape change in different crops in the same region, and often contrasting directions of change in different regions. While one might expect this with wheat and barley, that might be grown together in the same season, to find this across these cereals and millets is striking. The image above compares regional trends in grain length and width in free-threshing wheat, while the image below compares trends in the millets. Over the past 3000 years wheat and both millets tend to get longer in Central Asia; this is also true of both millets in East Asia. By contrast in northern Europe grains of all three species are becoming shorter over the same period. In Europe, wheats on average become shorter and fatter in north, but longer and skinner around the Mediterranean. In Central Asia wheat behaves more like southern Europe and the Near East. 

This all points to different selective environments in different regions. Sometimes shared across crops. Previously smaller scale, and shorter timeline studies have suggested that as wheat moved east to China grains became shorter and plumper (Liu Xinyi's "virtue of small grain size"), perhaps to make them more millet-like for cooking in East Asian boiling traditions. It is not clear such patterns hold up. Would such an explanation also be suitable for the trends in post-Roman northern European wheat? More problematic still is that the large dataset in Dal MArtello et al. (2025) is that decreasing grain length is seen in wheat starting in central Asia around the same time as its arrival in East Asia. These regions we might expect to have different cooking traditions and different cultural selection environments? The trend reverses around 2000 years ago with grains again getting larger.

An unambiguous explanation for this is elusive. It could be that there were some environmental factors in each region acting across crops. These need not be directly on grain size either, as grain size may scale allometrically with selection on other aspects of size, like plant height. Shorter and smaller plants might be more resistent to lodging in some kinds of weather or more drought tolerant. For example the Indian shot wheat, Triticum sphaeroccum,  has particularly short grains, as well as shorter plants, which seems to evolved twice in South Asia as adaptations to extremely high temperatures and evapotranspiration, even though sphaerococcoid grains reduce grain weight and overall yield (see Cheng et al. 2020).

The more general point is that crops have always been evolving and differ across regions. The foxtail millet (Setaria italica) grains at the head of this post contrast short plump grains from China (Lixian, Gansu) and skinner grains from India (Sanganakallu, Karnataka) both from the UCL archaeobotany reference collections. Explaining these differences may be hard, but what is clear that archaeobotany and systematic measurement of more assemblages can provide a window on tracking how regional populations varied across time.

Reference collections at UCL- a brief history

Recently published is a short account of the UCL archaeobotany laboratory reference collections, "Seeding and branching out: sixty years of a laboratory for plants in archaeology". The archaeobotany laboratory began in earnest in 1964, with the arrival of Geoffrey Dimbleby as Professor of Human Envionrment. He was a palynologist, who had contributed to archaeology through the reconstruction past environments through studying palaeosols in northern England, e.g. his book

The Development of British Heathlands and Their Soils (1962). By the end of later 1960s he had broadened his archaeobotanical interests, as represented by his book Plants and Archaeology (1967), and in the 1970s he began teaching an MSc-- among its early students was George Willcox, who went on to make important contributions on the archaeobotany of London, Afghanistan, and Syria (among other places). After Dimbleby's retirement in 1979, David R Harris TBA from UCL Geography became professor of Human Environment. David brought on board Gordon Hillman, first as research fellow (1981) and then lecturer (1983), and they established a quite famour MSc program which focused on archaeobotany on alternative years.Through these years and onwards, including since I joined UCL in 2000, our reference collections have grown. The have grown in geographical breadth and categories of plant materials, but they have also been enhanced through cataloguing anf storage, making them more accessible for teaching and research, including visitors who want come and consult for research. I am especalli thankful for the years of efforts at curation and cataloguing by Dr Sue Colledge, our honorary professor, who worked with Hillman and Harris as a research assistant in the 1980s, was emlpoyed to curate Hillman's collections for a couple of years from his reitrmement in 1998, and who was a post-doctoral researcher on numerous projects here in the 21st century.

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.

Archaeobotany lab at UCL refurbished and reopened

UCL Archaeobotany Laboratory

This past summer the UCL Archaeobotany Laboratory was refurbished and enlarged (slightly), thanks to funds from the A3RC project funded by the UKRI Research Infrastructure for Conservation and Heritage Science program. Over the past term we have moved collections and equipment back into the lab. This offers some improvements for teaching practical courses in the lab, such as my seed identification short course, also a MSc course (email me to get on the waiting list for future), and facilities for visiitng researchers who come to consult the collections for identifications. Over many years Dr. Sue Colledge has been cataloguing the extensive references (more 19,000 accession catalogued), a catalogue of which we aim to make available online soon. Dr Ayelen Delgado, the new technician for archaeobotanical collections is working on a new catalogue of legacy collections of archaeological plant remians. As part of our lab re-launch we have a new instagram account to feature modern and archaeological specimens, @archaeobotanylab, which will also report news coming out of the lab.

For my part is is high time I reactivated this blog with surveys of important finds from the world archaeobotany and critical reviews of publications, as I was known for a decade ago. Its time for me to provide some updates on some of my favorite topics, like rice, millets, domestication and archaeobotany in Africa, the Near East, India and China (among other places).

The archaeobotany laboratory here at the UCLInstitute of Archaeology has a been centre for research and teaching for over 60 years. Geoffrey W. Dimbleby (1917-2000) was appointed as Professor of Human Environment from 1964 (to 1979) [obit. by Harris], succeeding the famous archaeozoologist and geoarchaeologist Frederick Zeuner. (Zeuner's successors in zooarchaeology are still going strong here at the Institute too). After Dimbleby's retirement (1979) David R. Harris became Professor Human Environment (1980-1998), moving from UCL Geography. David was a great synthesist and theorist of domestication and agricultural origins. To enhance the more practical aspects of archaeobotanical research and teaching Harris recruited Gordon Hillman in 1981, who brought extensive plant collections from Turkey and Syria. Gordon Hillman tuaght and trained many archaeobotany students through 1980s and 1990s-- although the reference collection was then in a different and smaller room. Harris and Hillman retired in 1998, and I was lucky enough to be offered a lecturing position starting in 2000. We moved the collections and microscopes into its current space in 2000/01, the first academic year in which I attempted to teach practical archaeobotany at the Master's level. (I like to think my teaching and experience has come along way in the quarter century since then.)