Biology subjects

Cenac, Z.

Publications and source records attributed to Cenac, Z..

5 recordsLinked to original sources

bioRxiv2023

The global expansion from southern Africa by modern humans? Its signal may be shown more through the cranial shape of males than females

As the geographical distance between populations increases, populations are known to become more distant (dissimilar) in biological measures such as cranial shape. Relationships between geographical distance and biological distance are thought to be explained by modern humans having expanded from Africa. Expansion from Africa is also thought to explain why biological diversities (e.g., cranial shape diversity) decrease as geographical distance from Africa goes up. Research has suggested that modern humans expanded through different routes. If there were different routes, perhaps the relationship between geographical distance and cranial shape distance declines as the population (that distances are measured from) gets further away from Africa. This study used cranial shape measurements derived from the Howells data, and found that such a decline was suggested for males, unlike for females. It has been reasoned that variables which indicate the global expansion should signal an area of origin which is only in Africa. The relationship between geographical and cranial shape distances did not signal an exclusively African area. However, for males, the area was primarily in Africa. Overall, the relationship seemed to represent the expansion better amongst males than females. Congruently, cranial shape diversity declined more strongly for males than females as geographical distance from Africa accrued. To estimate which area of Africa the global expansion originated in, previous research pooled an estimate from genetic diversities, and suggested a southern origin. This estimate was supported when adding cranially-derived variables to the pooling, including the relationship between geographical distance and male cranial shape distance.

evolutionary biology↗

bioRxiv2023

X-chromosomal diversity may reflect climate (when considering human expansion from Africa)

Previous research indicates that a climatic signal is present in mitochondrial diversity, but absent in other genetic diversities (e.g., X-chromosomal) and cranial diversity. Such research included analysis which adjusted diversity for distance from Africa (i.e., to account for global expansion), and saw whether adjusted diversity is associated with climate. The indication of a climatic signal may be affected by the choice of African location from which distance is measured. To bypass this potential effect of location, some analyses in the present research only featured populations which are located outside of Africa. The present research (Studies 1 and 2) used various diversities which were sourced from previous research. Autosomal, X-chromosomal, mitochondrial, and cranial diversities were adjusted for distance from Africa. This adjustment was not used regarding Y-chromosomal diversity; a preprint suggested that Y-chromosomal diversity does not signify expansion from Africa. In Study 1, adjusted X-chromosomal diversity increased with minimum temperature. Conscious of replicability, Study 2 examined whether a climatic signal is present in X-chromosomal diversity when an alternative dataset is used; a signal was not detected. Other adjusted diversities, including (surprisingly) mitochondrial, were not found to be associated with minimum temperature. Data from one dataset, but not another, was supportive of a relationship between sex-biased migration and climate--it seems unclear if this relationship would underlie a climatic signal in X-chromosomal diversity. Therefore, it is uncertain i) if X-chromosomal diversity is associated with climate, and, ii) why there might be an association. Further replication research on this topic is called for.

evolutionary biology↗

bioRxiv2023

Y-chromosomal microsatellites and expansion from Africa

Research has suggested that Africa is the continent from which modern humans dispersed around the world. Some diversities are thought to trace this expansion; they decline as distance from Africa accumulates, and they suggest that the expansion originated within a range of locations in Africa. Previously, a decline was found regarding Y-chromosomal microsatellite heterozygosity. However, this diversity has been noted to suggest a non-African origin and, consequently, not look like it indicates expansion from Africa. Declines have appeared in other variables which are derived from Y-chromosomal microsatellites. These variables include effective population size, expansion time, and time to the most recent common ancestor. The present research inferred if these variables, and some Y-chromosomal diversities, indicate expansion from Africa. Variables which indicate the expansion could help with identifying which area of Africa the expansion started in. This research used variables previously derived from Y-chromosomal microsatellites. These variables were for populations from across the world (effective population size, expansion time, and time to the most recent common ancestor) or only in Africa (haplotype and repeat unit diversities). Regarding populations across the world, San were very high in each variable when considering distance from (southern) Africa. Without San, effective population size and time to the most recent common ancestor did not squarely indicate an African origin, and expansion time placed the origin wholly outside of Africa. When using San, each area was only in Africa. Amongst African populations, whilst both haplotype diversity and repeat unit diversity showed a geographical pattern of declining, only haplotype diversity suggested a completely African area of origin. A southern African origin was broadly indicated when a general estimate of the origin was produced from Y-chromosomal haplotype diversity alongside some other genetic diversities.

evolutionary biology↗

bioRxiv2023

Expansion of modern humans over the world: The origin when considering non-linearity

Types of diversity have been known to decline linearly with the rise of geographical distance from Africa. Declines have helped to suggest the area in Africa which holds the origin for the global expansion of modern humans. Research has, at times, explored if there is a non-linear relationship between diversity and distance from Africa. A previous suggestion was that non-linearity could affect where the expansion appears to have originated. Linear analysis with Y-chromosomal microsatellite heterozygosity has been contrary to the expansion from Africa, instead indicating an origin involving Asia; could this be attributable to non-linearity? The present study looked into whether there are non-linear relationships between distance and diversities, and approximated where the expansion began. This study used diversities from previous research - genetic (autosomal, X-chromosomal, Y-chromosomal, and mitochondrial) and cranial shape. The Bayesian information criterion was the statistic for comparing linear and non-linear (quadratic) models to indicate if there is a non-linear relationship. This criterion was also used to estimate where the expansion launched from. Autosomal microsatellite heterozygosity favoured a non-linear relationship. This may be due to South American populations. Mitochondrial diversity suggested non-linearity too, but not when minimum temperature was controlled for. Whilst non-linear relationships indicated that the expansion had its start in Africa, for autosomal microsatellite heterozygosity, the area of origin appeared to be rather affected by the type of model (linear or non-linear). Other diversities (e.g., Y-chromosomal) supported linear relationships. Therefore, non-linearity does not seem to explain Y-chromosomal microsatellite heterozygosity being unexpressive of the global expansion.

evolutionary biology↗

bioRxiv2022

Modern human expansion from (southern?) Africa

Previous research favours the idea that modern humans spread worldwide from Africa. For instance, through autosomal diversity, a geographical area of origin for this worldwide expansion is indicated to entirely be within Africa. It remained to be seen if this indication happens for certain variables such as Y-chromosomal diversity. There is disagreement regarding where in Africa the origin is. Perhaps a region of Africa may seem to be the origin because of non-African ancestry rather than the expansion. The present research considered whether some genetic and cranial variables indicate the expansion, and, furthermore, where in Africa the expansion started. Variables included, for example, autosomal diversity (in sub-Saharan Africa) which was adjusted for non-African ancestry, Y-chromosomal diversity, and cranial sexual size dimorphism. For each variable, it was seen if the estimated area of origin was solely in Africa. Moreover, to generally estimate the origin, a centroid was calculated from potential origins which were obtained in the present, and past, research. The area of origin was completely within Africa for each variable except one - for Y-chromosomal diversity, the area was possibly in Asia only. The centroid of the potential origins was in southern Africa, consequently supporting a southern African origin. The autosomal diversity of sub-Saharan African populations, adjusted for non-African ancestry, indicated a southern African origin. The adjusted diversity appeared to start declining from about 2,000-3,000 km away from the origin - this non-linear pattern may be explained by travelling which happened after the expansion, or the expansion entering locations in Africa which were already populated, to differing extents, by modern humans.

evolutionary biology↗