Cereals are a central resource in the human diet and are traditionally assumed to have evolved from wild grasses in the early years.
Neolithic, 12,000 years ago at the earliest in the Middle East, under the pressure of agriculture. The
discovery of cereal pollen in the 600-meter-long borehole made in Lake Acıgöl (southwest of Anatolia, Turkey) and dated 2.3 million years ago at the base, allows us to retreat more than two millions of years ago the appearance of cereals in ecosystems, and to question the paradigm of the domestication of plants in the Neolithic.
Location map of Lake Acigöl, in southwestern Turkey – after Demory et al., 2020 © V. Andrieu & The Conversation
Pollens of grasses, such as rye and cereal type (Cerealia-type), were identified throughout the Acıgöl survey. These pollens have the same morphological characteristics as current cereal pollen grains, with an average diameter greater than 40 µm and a large pore surrounded by a thick ring. As by definition cereals are cultivated plants, we called our old cereal pollens ”
proto-cereals To emphasize the fact that these pollens are identical. These cereals appear at the same time as spores of coprophilic fungi which complete their biological cycle in the faeces of mammals and which are characteristic of the presence of herds of large herbivores.
Pollen grains of Cerealia and Triticum sp. of Acıgöl (ACI), boring 3 (photos 1 – 7), of the Roman site of La Verrerie, Arles, France (photo 8) and of Gardouch, France, current wheat (photo 9). L: maximum length (µm) © V. Andrieu & The Conversation
This resemblance is clearly visible in the figure above, where we have collected fossil cereal pollens from Acıgöl (photos 1-7) and from the Roman period (photo 8), not modified by modern agricultural practices, and pollens of current cereals from a wheat field in the Lauragais agricultural plain in France (photo 9).
Proto-cereals are very present around 2.2 million years ago (Ma), then a decline occurs from the mid-transitionPleistocene (from 1 to 0.8 Ma), when the climate becomes cooler and a change in fauna occurs. The comparison of fossil pollens with those currently measured on the lakeshore of Acıgöl and its surroundings, shows that cereal pollens are almost absent, even in environments with wild grasses considered as ancestors of cereals as
the eelope (Aegilops) or cereals such as barley (Hordeum).
Our interpretation is that the proto-grains come from wild grasses that grew naturally in the Anatolian steppe. Their emergence and predominance may have been favored by ecological disturbances linked to the presence of large herds of herbivores which came to drink in the Great Lakes region where Lake Acıgöl is located. The trampling of herds of large mammals, the nitrogen enrichment of the soil with excrement and the grazing of the steppe by animals have been able to modify the genome of the proto-cereals naturally present in Acıgöl and thus promote the emergence of modern cereals. The fossils found in this region bear witness to an abundance and great diversity of herbivores. Among these, paleontologists have identified an extinct species of mammoth and rhino, several species of horses and deer, a primitive okapi, a paleo-camel, a large bovid that is now extinct, and many antelopes. The populations ofHomo erectus (the’
Koçabas man), present in the Great Lakes region between 1.2 and 1.6 million years ago, were able to coexist with a rich and diverse megafauna on which they were largely dependent.
Core collection of the geological and mining service of Ankara (Turkey) © V. Andrieu & The Conversation
The ancestors of cultivated trees typical of modern Mediterranean agriculture are also present in the lake sediments of Acıgöl. Other potentially edible plants have also been identified. They correspond to 54.4% of the plants identified in the pollen assemblages. These results bear witness to the potential wealth of accessible food resources on which human and animal populations could feed themselves.
In recent years, new biological and archaeological data from hominin sites have improved our knowledge of the beginnings of agriculture and the methods of its implementation. In the Levant, at Ohalo II, seeds of proto-cereals and scythes in flint were found around 23,000 years old. Further north, in the archaeological site of Gesher Benot Ya’aqov, seeds of proto-cereals and pollens of currently cultivated trees have been identified between -750,000 to -820,000 years.
Moreover, recent genetic data indicate that the emergence of agriculture did not occur in one place and at the same time at the start of the Neolithic (this is the “Fertile Crescent” hypothesis), but that ‘it is an evolving and multiregional phenomenon. It is therefore possible that hominin populations have developed transient forms of “proto-agriculture”. We know, in fact, that the domestication processes were discontinuous, with phases of stopping and restarting. The Acheulean lithic tools, characterized by bifaces of symmetrical shape, testify to the rather advanced cognitive capacities of the human populations of the Lower Pleistocene who could frequent the shores of Lake Acıgöl. Hominin populations may also have taken advantage of this opportunity to diversify their diet with wild plants that are easy to collect and rich in nutrients, as is the case with the hunter-gatherer populations that still exist today in some parts of the country. our planet.
Agricultural hearths and dispersal of agriculture (adapted from J. Diamond – 2003) © Chamois rouge / Wikimedia CC BY-SA 3.0
The question of the emergence of the Neolithic with the domestication of plants and animals has been debated for decades. It has been the subject of innumerable studies, in most cases carried out by archaeologists and geneticists who have focused either on the plant macro-remains of archaeological sites, or on the genomic history of cultivated plants. The study of natural environments (wetlands, lakes), such as Acıgöl, and their microbiological content has so far been largely neglected to address this question.
What happened in the Neolithic Age, when humans changed from a hunter-gatherer way of life to a farmer way of life? Did they reproduce the conditions that existed two million years ago? Has there been a new stage in human-related cereal speciation? The proto-cereal pollens of Acıgöl seem to indicate that the genetic modification of cereals may have been a natural process in place long before the onset of agriculture, and that the conditions were already in place when human populations passed from societies. from hunter-gatherers to agricultural societies.
Our results allow to rephrase an important conundrum about human evolution and to question the long-held paradigm that humans were the progenitors of cereals, while it seems, rather, that cereals arose naturally, humans having simply accelerated their expansion If this is confirmed by the presence of proto-cereal pollens in sediments of the Lower Pleistocene or in older sediments in other regions, it will require a total overhaul of our overall view of the history of human nutrition. Preliminary research carried out in travertines from Denizli (Turkey) and Marseille (France), dated from 1.6 to 1.1 Ma, has already made it possible to highlight the presence of proto-cereal pollen.
This analysis was written by Valérie Andrieu, assistant professor in paleoecology at Aix-Marseille University (AMU).
The original article was published on the website of The Conversation.
