| 1. |
- Breton, Gwenna
(författare)
-
Human demographic history : Insights on the human past based on genomes from Southern through Central Africa
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Evidence from paleontology, archaeology and population genetics support that modern humans originated in Africa. While the out-of-Africa event and subsequent colonization of all continents are well documented, human history in Africa at that time and before is less studied. Some current-day hunter-gatherer populations trace most of their genetic lineages to populations who inhabited Sub-Saharan Africa until the arrival of farming. They are informative about human history before and after the arrival of farming.I studied high-coverage genomes from two such groups, the Khoe-San from Southern Africa and the rainforest hunter-gatherers from Central Africa. I generated a total of 74 genomes, significantly increasing the number of genomes from Sub-Saharan African hunter-gatherers. I compared several versions of a commonly used pipeline for high-coverage genomes and showed that using standard ascertained reference datasets has no significant impact on variant calling in populations from Sub-Saharan Africa. Using the full genome information, I described the genetic diversity in the Khoe-San and in the rainforest hunter-gatherers and showed that gene flow from agropastoralist groups increased the Khoe-San genetic diversity. I also detected a signal of population size decline in the Khoe-San around the time of the out-of-Africa event, and I evaluated the power of the method to detect bottlenecks by applying it to simulated data. I investigated the history of modern humans in Africa by estimating divergence times between populations and applying an Approximate Bayesian Computation analysis. We confirmed that the earliest divergence event was between the Khoe-San ancestral lineage and the rest of modern humans, ~250-350 kya. I also showed that the possibility of high gene flow should be incorporated in models of human evolution.I furthermore examined SNP array data for two BaTwa populations from Zambia and showed that 20-30% of their autosomal diversity is hunter-gatherer-like. The estimated times for the admixture between a presumably local hunter-gatherer population and incoming agropastoralist groups are consistent with archaeological records.In this thesis, I investigated questions related to human history in Sub-Saharan Africa, from the emergence of modern humans ~300 kya to recent events related to the expansion of farming.
|
|
| 2. |
- McKenna, James, 1987-
(författare)
-
Divergence, admixture and continuity in the human past : Demographic inference using ancient and modern genomes
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Demographic forces shaping the genetic variation we observe today can include population divergences, admixture events and continuity through time. The advancement of high-throughput sequencing technologies, together with developments in molecular and bio-informatics methods, mean the number of ancient genomes available for inference has risen steeply. To make effective use of aDNA however, inference tools need to be developed that account for temporal as well as geographic sampling of genomes. Here I have developed, evaluated and applied methods for estimating divergence times between ancient and modern populations. I used simulation to study the sensitivity of these approaches to violations of model assumptions, before applying them to study the history of population divergence between pairs of populations from a global panel. Non-tree-like demography is common in the human past, with evidence of ancestral structure in the form of archaic admixture in the genomes of all non-African modern humans. Using SNP-array data collected from 118 ethnic groups in the Philippines, I show that the highest levels of Denisovan ancestry are found among the Ayta Magbukon, further highlighting the complex history between modern human groups and the archaic hominins occupying Eurasia before our arrival. Among the most important contributions population genetics has made to the study of the human past is the demonstration that cultural transitions and spread of technologies were often associated with migrating groups of people. This can result in the admixture, displacement or replacement of populations, and aDNA provides us with the opportunity to assess these trends directly through time. I developed a statistical tool to detect population continuity through time, evaluating its performance using simulation. Applied to a dataset of ancient genomes from Early Neolithic Scandinavia, I demonstrate population continuity in the hunter-gathering Pitted Ware culture, despite these people overlapping both geographically and temporally with farmers of the Funnel Beaker culture. In another study of the hunter-gatherer ancestors of the San people of southern Africa, I show evidence that this group exhibited long-term population isolation, remaining unaffected by admixture from outside southern Africa until surprisingly recent times. Using these ancient genomes, I provide further evidence that all modern Khoe-San populations exhibit significant levels of admixture with people of non-Khoe-San ancestry, demonstrating the strong impact migrations in this region have had in the past ~2,000 years.
|
|
| 3. |
- Simões, Luciana G., 1986-
(författare)
-
Uncovering the Past through ancient DNA : The Fate and Legacy of the last hunter-gatherers in Western Europe and Northwestern Africa
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The genetic analysis of ancient human remains has revolutionized the study of human history, opening a direct window onto the demographic and evolutionary events that shaped our species' past. I use state-of-the-art ancient DNA methodologies, from sample collection and DNA extraction to data analysis, to study the ancient past of the western Mediterranean region, where climate does not favour DNA preservation. After the Last Glacial Maximum, amenable climatic conditions enabled the development of agriculture in the Levant, initiating the Neolithic period. In Europe, the transition from foraging to farming was driven by the migration of people from Anatolia, but in North Africa, evidence indicates a cultural diffusion, instead of population replacement. In this thesis, I show that this transition was in fact ignited by the migration of early farmers from Iberia. Moreover, a different migration wave, originating in the Levant and expanding within Africa, was associated with pastoralism in that region during the Neolithic. While the Neolithic transition is one of the most studied periods of pre-history, earlier periods are comparatively under-studied. Using whole genome sequencing data for 36 hunter-gatherers from Iberia and France, I observed that genetic lineages rooted in the Palaeolithic, survived throught the Mesolithic. Mesolithic hunter-gatherer populations formed social units that were not based on familial bonds; exchanges between groups avoided consanguinity. Coexistence with the first farming communities resulted in unidirectional admixture patterns, as we do not find gene flow from farmers to the last hunter-gatherers. Finally, using a multidisciplinary approach to study an exceptional individual of African descent buried in a Mesolithic shell midden, we find that the burial of this man during the transatlantic slave trade period could be an example of the maintenance of African cultural practices by African people displaced to Europe. My thesis highlights the power of ancient DNA analysis to uncover events and patterns of the human evolutionary history, but also that integrative approaches, where different lines of evidence are combined, can lead to exciting findings.
|
|
| 4. |
- Vicente, Mário
(författare)
-
Demographic History and Adaptation in African Populations
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Africa is the continent where modern humans originated and yet, African demographic history remains largely unknown. Through analyzing the genetic composition of extant and extinct individuals, it is possible to reveal signals of past demographic history and adaptation. In this thesis, I applied population genetic methods to investigate both deep African history and demographic changes associated with the migrations of farmers in Africa. While Paper I and II assess the genomic landscape before the arrival farming groups, Paper III, IV and V focus on the demographic patterns associated with the emergence of various African agro-pastoral societies and how shifts in ways of subsistence resulted in different selective pressures on the genomic level. The genomes from Southern African San hunter-gatherers harbor the earliest diverging lineages and represent the first population divergence event within the modern human phylogeny. However, gene-flow from farming groups has complicated the investigation of genetic relationships between different San groups. In Paper I, I established that Southern African hunter-gatherer genetic diversity fitted an isolation-by-distance model when genomic segments that trace their ancestry to farming groups were excluded. Paper II confirmed that all extant Southern African hunter-gatherers received admixture from farming groups, through comparison with ancient DNA data from three 2,000-year-old southern African Stone Age individuals. New date estimates for the first population divergence event in the modern human phylogeny, based on the Stone Age individuals, coincided with a period in the fossil record associated with transition between archaic humans into anatomically modern humans. Paper III assesses the genetic variation of four ancient Iron Age women from current-day South Africa. I was able to further refine their genetic profiles, which were closest related to southeast Bantu-speaking farmers from current-day South Africa. In Paper IV, I propose that the emergence of pastoralism in Southern Africa arrived through a male-driven migration of East African Afro-Asiatic related groups, who introduced their pastoral subsistence practices and livestock into Southern Africa. In Paper V, I investigated the history of the Fulani population and demonstrated how a shift in subsistence practice triggered different selective pressures in the Fulani. The pastoral Fulani from the Western Sahel show relatively high frequencies of the European-associated Lactase Persistence (LP) variant. Here, I propose that the LP mutation were introduced into Fulani genomes through contact with a North African group(s) who themselves carried European admixture. Additionally, by performing the first genome wide association study (GWAS) on the lactose digestion phenotype, I confirmed the association with the MCM6/LCT locus and identified a possible association between glycemic levels after lactose intake and the SPRY2 gene. Furthermore, in addition to the LP trait, I also identified other potential signals of local adaption related to the pastoralism lifeway of the Fulani. This thesis provided further insights on how the African genomic landscape was shaped through time, influenced by the environment, interactions between different groups and adaptations to different lifeways.
|
|
