Thursday, March 12, 2020

Farmers Mostly Replaced Hunter-Gathers In Sicily

Eurogenes notes a new paper confirming the modern paradigm regarding  the Neolithic transition (i.e. the manner in which herding and farming replaced hunting and gathering) in most of Europe. 

The modern paradigm is that hunter-gather populations were largely replaced by gender balanced farmer migrants, derived predominantly from Anatolian farmers, who in turn were derived from Anatolian hunter-gatherers. In Southern Europe, the Anatolian farmer migration was via the Balkans and Greece, who were part of the Cardial Pottery (CP) Culture was a subset of migrant farmers who were subtly distinct from the Anatolian farmers who migrated into Europe further to the North giving rise to the Linear Pottery Culture (LBK).

(A fine point. Balkans and Greek farmers may not have been CP as found in Spain and may instead of been something subtly different from the.)

The modern paradigm, supported by ancient DNA, superseded a paradigm popular from the 1960s to roughly the 1990s in anthropology, in which cultural diffusion of technologies and ideas to people who already lived in a place that experienced a change in material culture, as opposed to population replacement, was emphasized, under the motto "pots aren't people." Almost across the board, there was some introgression of hunter-gather individuals into migrant farmer communities, but this made up only a small portion of the total ancestry of the new farming population.

The new paper also establishes that there was ongoing population exchange between the Near East and Europe of hunter-gather peoples during the pre-Neolithic, post-glacial era, rather than there being just a single pulse of hunter-gatherer repopulation of Europe that then became completely static until the Neolithic revolution.
Southern Italy is a key region for understanding the agricultural transition in the Mediterranean due to its central position. We present a genomic transect for 19 prehistoric Sicilians that covers the Early Mesolithic to Early Neolithic period. We find that the Early Mesolithic hunter-gatherers (HGs) are a highly drifted sister lineage to Early Holocene western European HGs, whereas a quarter of the Late Mesolithic HGs ancestry is related to HGs from eastern Europe and the Near East. This indicates substantial gene flow from (south-)eastern Europe between the Early and Late Mesolithic. The Early Neolithic farmers are genetically most similar to those from the Balkan[s] and Greece, and carry only a maximum of ~7% ancestry from Sicilian Mesolithic HGs. Ancestry changes match changes in dietary profile and material culture, except for two individuals who may provide tentative initial evidence that HGs adopted elements of farming in Sicily.

van de Loosdrecht et al., Genomic and dietary transitions during the Mesolithic and Early Neolithic in Sicily, bioRxiv, Posted March 12, 2020, doi:


Guy said...

Hi Andrew,

If we have ~7% local HG in the Neolithic Sicily population is that proportional to the difference in carrying capacity between HG and farming?


andrew said...

@Guy In the Egyptian Neolithic, carrying capacity for farming was more than 100x the carrying capacity of the preceding hunter-gatherers in the same place which was far more abundant (the Nile River Valley) and thus has a far higher carrying capacity that the deep forests and deserts that are marginal for farming where hunting and gatherers are found in modern times.

I think that the Egyptian Neolithic was an extreme case, but I also very much doubt that the carrying capacity for farming was only 13 times that of the carrying capacity for hunter-gatherers.

I think a better narrative and mental model would be of farmer men coming in gender balanced families who lose wives in childbirth or due to disease or accidents who can't easily replace those wives with members of their own culture since in a gender balanced migration all women are taken and the migration is too distant to replace them, so they fill the shortfall with local women, and also marry elite local women to seal alliances with local tribes to maintain peace in the short run where the remaining hunter-gatherers live on land ill suited to farming like mountainous and heavily forested areas and areas with poor soils, until the hunter-gathers are gone and the cumulative effect of hunter-gatherer introgression into farmer communities has been diluted into the gene pool after a few generations.

andrew said...

Here is what one paper estimates as of May 2005: "Dolukhanov [16] estimates the carrying capacity for hunter-gatherers in a region of temperate forest to be 7 persons per 100 km². Ammerman and Cavalli-Sforza [4] suggest that the carrying capacity for farmers is a factor of 50 larger, which yields K = 3.5 persons/km²." So relative carrying capacity proportions would be something like 2%, and distinct hunter-gather populations persisted in relative isolation from nearby farmer populations at any given place for a rule of thumb 1000 years (34 generations). A narrative where introgression takes place a rate of perhaps 1% per generation in the first couple of generations (about 1 woman per 50 men when farmers are less well established and need treaties quick) and 0.16% per generation (about one new woman per 300 total women in the community per generation) for the next thirty-two generations (after which there are no hunter-gatherer populations that are distinct and with the exogamy factor increasing for the hunter-gatherers each generation as their numbers dwindle facing pressure from farmer expansion) probably makes more sense.

andrew said...

Also supporting a model with low initial admixture into first farmers is mtDNA in the earliest farmer which had a very small hunter-gatherer component. (Sicily in this sample is more mature including times long after the initial Neolithic.)

"The very low frequencies of hunter–gatherer lineages (0–2.27%), in the STA, LBKT and LBK sample sets (figure 3) indicate that the arrival of agriculture in the Carpathian Basin and Central Europe was accompanied by a strong reduction of the currently known Mesolithic mtDNA substratum, resulting in a distinct and contrasting mtDNA haplogroup composition, and significant differences between hunter–gatherers and early farmers (figures ​(figures22 and ​and3;3; electronic supplementary material, figures S1–S3, table S1, datasets S7–S10, S12 and S13). This scenario is consistent with coalescent-based simulations that have revealed genetic discontinuity between Central European hunter–gatherers and LBK communities [28,38]. The detection of haplogroup U5b in the Mesolithic individual from Croatia matches previous observations, which describe sub-haplogroups of U as characteristic mtDNA substratum in Mesolithic Europe [28,39]. Residual Neolithic hunter–gatherer isolates, as reported from Central Europe by Bollongino et al. [30], probably also existed during the Early Neolithic of the Carpathian Basin, as shown by the hunter–gatherer ancestry of the sixth millennium BC human remains from an Early Neolithic Körös settlement pit in eastern Hungary [41]. According to the low proportion of hunter–gatherer mtDNA lineages in the LBK gene pool, we assume that admixture between hunter–gatherers and colonizing LBK farmers was also low in Central Europe.

Considering the relative size and speed of the LBK expansion, we have to presume a substantial population growth during the earliest LBKT, which might have resulted in a population pressure and led to emigration from Transdanubia [62]. Although such a radical population size increase was not palpable from the Early Neolithic archaeological records [7], recent extensive archaeological excavations have revealed large-scale LBKT settlements in western Hungary [9,63,64], suggesting larger source communities for expansion than previously assumed."

andrew said...

But, this paper from 2017 assumes a 10x carrying capacity difference in the areas it is studying.