The Neolithic Revolution: Pre-existing Cultural Differences Leading To Neolithization

Introduction

There had already been some research conducted in the field of Neolithization before Leonardi M et al, published the paper titled ‘An earlier revolution: Genetic and Genomic analyses reveal pre-existing cultural differences leading to Neolithization’. However, most of the initial research and the papers which have the most significant results were conducted in the mid-1990s and late-1990s. Recently there has been a small increase in the research concerning Neolithization.

A population which transitions from hunter-gather to food producers are said to undergo a Neolithic revolution. This means that a population which normally gathers food from hunting etc… over time begins to transition to a population where farming etc… is the main source of food. This can occur for a multiple of different reasons, with the main one being more individuals in a population becoming food producers and isolating the original hunter-gather populations. The transition from hunter-gather to food producer is regarded as one of the most important developments in the prehistory of humans. This is because of the major effects the shifting from the type of food collecting to the other has on the cultural threshold, which are normally characterised by vast shifts in economy, technology, ideology, settlement and social organisation combined.

The international NEOMAP (Neolithization and Modernisation Landscape History on East Asian Inland Seas) Project, was specifically designed to provide insights into a series of unique cultural transformations in East Asia.

Zvelebil M and Dolukhanov P (1991) suggests that the Neolithic transition from hunter-gathers to food producers was a relatively slow process. The transition begun to occur due to the adoption of exogenous cultigens and domesticates by the population of hunter-gathers. This may be due to hunter-gathers already engaging in some form of husbandry of local resources. Eastern and Northern European populations who undergo contact and exchange with Bronze Age of Central Europe had a vital and extended influence on the process of adoption of farming in Eastern and Northern Europe. It is said that in Europe, the transition is a slow process, meaning that the societies in which would have resulted from the transition would be consisting of partly hunter-gathers and food producers begun to emerge. These societies could be regarded as having characteristic social and economic organisation of their own.

Neolithization was first theorised in the early 1950’s by Robert and Linda Braidwood. They had theorised that Jarmo, a small village in Iraq, was one of the first villages which saw a Neolithic transition occur. Whilst Jarmo was not the first village to have been theorised to undergo Neolithic transition, it may be of vital importance in bridging the gap of knowledge which surrounds the area of Neolithic revolution. The domestication of plants and animals provided the ability for populations to generate a stable food supply, consequently, due to this domestication of plants and animals, it has allowed for so called ‘proper village life’ to emerge. It isn’t entirely a coincidence that as food producers become more prevalent in populations certain crafts begun to rise in popularity. These crafts included architecture, pottery, weaving and metallurgy.

This paper states that the earliest estimates state that the first appearance of food production occurred approximately 8,000 years ago. The earliest clearly defined village assemblages are in the Near East, with seemingly six separate villages; Sialk I in North Central Iran, Hassuna and Nineveh in northernly Iraq, basal Amouq materials and the ‘Neolithic’ of Mersin in Syro-cilicia and Fayum in lower Egypt.

Jarmo however, by no means has been able to close the gap in archaeological knowledge between the stage of hunter-gathers and food producing. The paper suggests that Jarmo poses the ability to be the most substantial assemblage available nearest to the beginning of food production.

Results

The paper was written by Leonardi M et al, (2017) looks at three different regions, Siberia, South East Asia and Africa and looks at the pre-existing evidence of when the populations from the region transitioned from hunter-gather to food producers. The paper also looks at two different datasets. The first dataset concerns itself with the linkage disequilibrium (LD) of genome wide SNPs (using a software called NeON), with the second dataset concerns itself with the MSMC estimates (Multiple Sequentially Markovian Coalescent). The results of the research are concerned with both datasets.

Demography

For each of the three regions, they computed the ratio of population sizes amongst all pairs with different subsistence regime. Leonardi M et al, did this to allow for the formal investigation of how populations of hunter-gathers transitions into populations of food producers and how these populations differed through time. If the ratio was 1 then it would indicate that there was no difference between the two categories. However, the actual results which were obtained through this research was that for all three regions, the ratios were calculated to be significantly higher for food producers compared to hunter-gathers. This means that there was always a higher number of individuals who were food producers than hunter-gathers in a population. The minimum ratio which was calculated was 1.1 (on average) in the favour of food producers. For each of the three regions and the two datasets the trajectory of the minimum ratios of hunter-gather to food producers were also calculated, this calculation showed a gradual increase in the number of food producers to hunter-gathers.

Climate

Leonardi M et al, then tested the three regions and the two datasets to see if the differences seen between them were due to the climate that the populations were living in, as the three regions, which were chosen for this study all have different climates. Africa has a hot climate, Siberia has a climate which is described as sub-arctic and South East Asia has a tropical climate. However, the differing climates doesn’t seem to be an explanation as to the differences in the results for the regions of Africa and South East Asia. This is because as according to Leonardi M et al, the estimates for the values of the annual Net Primary Productivity (NPP) for the populations in these two regions were not consistently skewed in favour of future food producers. Siberia, however, seems like a different story. The food producer populations in Siberia seemingly inhabited areas which began to favour the food producers. This is an example of the climate in which the populations live in influencing the populations. The hunter-gathers inhabited an area where it began to favour the food producers, which ultimately lead to the decline of hunter-gathers in Siberia. Calculation of the number of effective individuals (Ne) against NPP revealed that the ratio of food producers to hunter-gathers in Siberia was already substantially higher than 1, way before the advent of food producers. This ratio (Ne/NPP) for Africa and South East Asia increased rapidly ~10-12,000 years ago. This increase suggested either an increase in the number of effective individuals sustained by the same resources or it could indicate immigration occurring into these regions. This ratio for Siberia remained constant through time.

Test for bottleneck in hunter-gathers

It is suggested that a potential bottleneck occurring may be the reason for an underestimated Ne. Leonardi M et al, states that it is a possibility that the most modern-day hunter-gathers are likely to have undergone repeated phenomena of fragmentation and/or demographic crisis. If this is true, then they expect that their results could reflect this to a point in which it would be unable to quantify a methodological bias. This is ultimately meaning that it may not be feasible to discriminate between any small population sizes and any recent bottlenecks which may influenced an originally large population size.

MSMC estimates are much more robust regarding bottlenecks. Comparing the results form the NeON dataset and MSMC estimates for all the regions populations involved in the study (a total of 12 populations), shows that the individual trajectories do indeed seem different. However, this difference in the trajectories is seen when using different investigative models. This trait is also seen in all lifestyle, not just hunter-gather, therefore it is not a unique trait to hunter-gather. The overall pattern when comparing lifestyles does remain the same in both datasets.

Migration

Leonardi M et al, mentions an assumption that they had to assume for the study to be reliable and for it to be more of a success. The assumption was that the populations which were involved in the study were assumed to have lived in the same region for the past 20,000 years. This assumption had to be made to rule out the possibility of long-distance migration. Allowing for a more reliable set of result. They tested this assumption for South East Asia, where it is speculated that the populations of South East Asia have derived from at least two waves of advance. The Austronesian expansion, the more recent expansion, has been documented in the archaeological record. The expansion is said to be the spread of food producers from continental Eastern Asia associated with the diffusion of Neolithic cultures and technologies. The Neolithic diffusion occurred ~4,000 – 6,000 years ago.

Two main routes have been proposed for it; ‘Fast Train’ and ‘Slow Boat’. The ‘Fast Train’ model states that the expansion began in China and then slowly spread through Taiwan until it eventually reached the then island of South East Asia and Oceania, whereas the ‘Slow Boat’ scenario states that the spread initially came from mainland South East Asia.

For the above methodologies to be accounted for in the results, Leonardi M et al, and their team calculated the ratio of Ne in South East Asia from dataset 1 (LD of SNPs) following three separate models; the two as mentioned before ‘Fast Train’ and ‘Slow Boat’ and a new model ‘Cultural Diffusion’ (when populations acquire new practices and cultures from other populations). Under the ‘Cultural Diffusion’ model, Leonardi M et al, associated each Austronesian population the Net Primary Productivity for that region as well as where the populations are now living. However, the ‘Fast Train’ and ‘Slow Boat’ models are both associated the net primary productivity of the source region, respectively China and Cambodia. The overall pattern of these results showed an increase in more recent times, with this increase not varying a significant value between the three separate models. However, the main difference which was observed between the three models was that the minimum ratio being higher under the ‘Fast Train’ scenario. The reasons for this higher minimum ratio in the ‘Fast Train’ scenario was due to the estimates of net primary productivity values which were observed in Taiwan and South Eastern Asia. A direct consequence of the higher net primary productivity values was that the number of effective individuals per unit of net primary productivity becomes much higher for food producers which are based in more temperate regions such as China as the those which are based in more tropical areas.

What do the results mean?

The results which Leonardi M et al, obtained through their study have shown that there is some evidence that there was a transition from hunter-gather to food producers even before the Neolithic Transition. The results also showed that this divergence seemed to begin ~20,000 years ago, whilst the divergence started to become much more prevalent in the populations between 10-12,000 years ago in South East Asia and Africa. There is some level of uncertainty, however, surrounding the results which were obtained. This uncertainty is seemingly unavoidable and impossible to eliminate from the results. The results which Leonardi M et al, collected through their study matched the results that have already been obtained when looking at the comparisons of the two types of populations, hunter-gathers and food producers.

The paper by Zheng et al, (2012) is an example of a paper that was published a few years before the Leonardi M et al, paper. However, with the results of this paper and the paper written by Zheng et al, both complementing each other means that the results from Leonardi M et al, have a significant effect on understanding Neolithization. As the results match, it allows for Leonardi M et al, to be confident in their results and assume that their results are reliable.

The paper by Leonardi M et al, has been cited by another paper published in 2018 written by Natali E and Forgia V (2018). In this paper they reference Leonardi M et al, and what the results obtained from the study mean for the future of the field of Neolithization. Natali E and Forgia V, talks about what modalities that are involved in the Neolithization process and reference the genomic analysis that Leonardi M et al, show that the demographic growth that is normally associated with a Neolithic Revolution has been dated back to before originally thought. Leonardi M et al, paper states that the differences between the hunter-gathers and food producers, appeared well before the Neolithization process took place.

As the paper by Leonardi M et al, has ben cited by another paper, it means that the results that Leonardi M et al, obtained are reliable and have the chance of being involved or even being the basis of further research into the Neolithic Transition event.

Conclusion

To conclude, Neolithization as an area of scientific research has had a far bit research conducted to give a base understanding of how hunter-gathers transitioned to food producers. However, there is still a lot of more understanding to gain through more research. The paper by Leonardi M et al, is a good starting point in beginning to understand in more depth Neolithization. The paper by Leonardi M et al, begins to investigate the genomic evidence in pre-existing population to see if there is evidence of the Neolithization process. Whilst Leonardi M et al, paper is a step in the direction of full understanding of the Neolithization process, there is still plenty more research to be conducted in this field to widen our knowledge of the process. This can be seen in the paper by Natali E, Forgia V (2018), which sites Leonardi M et al. There is still more research that can and needs to be conducted to flesh out our knowledge of Neolithization.

References

1. Braidwood RJ, Braidwood L. Jarmo: A village early farmers in Iraq. Antiquity. 1950;24(96):189-195
2. Leonardi M, Barbujani G, Manica A. An earlier revolution: Genetic and genomic analyses reveal pre-existing cultural differences leading to neolithization. Scientific reports. 2017;7(1):3525.
3. Natali E, Forgia V. The beginning of the Neolithic in southern Italy and Sicily. Quaternary International. 2018;470:253-269
4. Uchiyama J, Gillam JC, Hosoya LA, Lindström K, Jordan P. Investigating neolithization of cultural landscapes in east Asia: The NEOMAP project. Journal of world prehistory. 2014;27(3-4):197-223
5. Zheng H, Yan S, Qin Z, Jin L. MtDNA analysis of global populations support that major population expansions began before Neolithic time. Scientific reports. 2012;2:745.
6. Zvelebil M, Dolukhanov P. The transition to farming in eastern and northern Europe. Journal of World Prehistory. 1991;5(3):233-278.