2022-04-08 14:29:42
When an archaeological or paleontological site is studied, those of us who are not experts in the field tend to think that what is found there are fossilized remains of bones or, if the site is linked to human activities, vessels or tools that have managed to resist the passage weather. However, in a site there are many more things and each of them tells a part of the story. The tiniest pieces of the immense puzzle with which archaeologists and paleontologists try to reveal the events, creatures and circumstances of the past are tiny, microscopic, and come from the plants that grew at that time and place. They are pollen grains and spores.
Pollen is nothing more than the masculine contribution of plants to reproduction, as are spermatozoa in animals. Logically, plants cannot move from one place to another, so they release pollen in huge quantities and wait for the wind, water or animals such as insects, birds or bats to take it to its destination, which is none other than the organ feminine of plants
What many of us could not suspect is how extremely resistant a pollen grain is. Our guest, the researcher from the Institute of History José Antonio López Sáez, explains that they are protected by a chitin cover, that is, the same substance that forms the hard parts of insects, and provides them with a protective shield that allows them to resist the pass of the time. Thus the pollen released by plants thousands, even millions of years ago, can remain stored in the sediments at the bottom of lakes, in peat bogs or on land. Discovering and identifying these pollen grains is the task of paleopalynologists, researchers who, like José Antonio López Sáez, study ancient pollens.
The paleopalynologist’s work is complemented by that of archaeologists or paleontologists because it allows obtaining information about the ecosystem at the time when a site was formed. To study ancient pollen, researchers often drill into sediments and extract cylindrical cores containing chronologically stored remains, so that deeper deposits correspond to older times. An adequate treatment of the control allows to release the pollen grains stored in it and thus obtain a sample that must later be analyzed with a microscope.
Each plant species or each family of plants has its pollen and, depending on the shape of the external cuticle, the families and even the plant species that generated it can be identified.
The study of pollen from past times can provide information that complements the knowledge we have of certain historical periods. A good example is the work recently published in the journal Nature Ecology and Evolution by an international team of researchers including José Antonio López Sáez. The study analyzes a period of time marked by the Black Death pandemic, which is thought to have killed half the European population between 1347 and 1352. Although there is a multitude of data from that terrible period, obtained mainly from comments in sources Medieval writings from some areas of Western Europe, our global knowledge of what happened is still limited, because the information is restricted to urban areas when the majority of the European population was, at that time, rural. The work carried out by José Antonio López and his colleagues expands knowledge about that terrible pandemic thanks to the study of the pollen that was stored in 261 sites located in 19 current European countries. In those places, samples of the sediments in lakes and wetlands were taken and the pollens stored during the century were studied. XIV. The analysis of the different types of pollen made it possible to evaluate, among other data, the abundance of cereals, a clear index of the capacity of agricultural societies to till the land. Thus, some regions show a substantial change in vegetation during the years of the pandemic and after. The amount of pollen from cereals decreased, while pollen from other wild and forest plants increased in parallel, a change probably due to the fact that the region suffered high mortality and, as a consequence, many arable lands were abandoned. Changes in vegetation, indicators of livestock activities, were also studied.
The work reveals that the pandemic was immensely destructive in some areas, but in others it had a much milder effect. The results indicate that there was a sharp agricultural decline in several regions of Europe, which is consistent with analyzes of historical sources, especially in regions of Scandinavia, France, western Germany, Greece and central Italy, where high mortality occurred. At the same time, there is much evidence of continuity and uninterrupted agricultural growth in regions of central and eastern Europe, and various regions of western Europe, particularly in Ireland and Iberia. Until now it was thought that the bacterium that causes the Black Death (Yersinia pestis) had spread uniformly throughout Europe, something that, according to the results of this study, was not the case.
I invite you to listen to José Antonio López Sáez, pelopalinologist, researcher of the Environmental Archeology Group in the Department of Archeology and Social Processes of the Institute of History.
Reference:
Izdebski, A., Guzowski, P., Poniat, R. et al. Palaeoecological data indicates land-use changes across Europe linked to spatial heterogeneity in mortality during the Black Death pandemic. Nat Ecol Evol 6, 297–306 (2022). https://doi.org/10.1038/s41559-021-01652-4
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