A Worldwide Survey Of Human Male Genetic Demographic History

Current models of human evolution differ in detail, but all include a recent origin in Africa and an expansion, both geographical and demographic, of fully modern humans from a small African population to the current large worldwide population within the last -100,000 years. Many analyses of worldwide DNA datasets support the hypothesis of serial founder events starting from a single origin in sub-Saharan Africa and leading to the Americas as the last continents to be inhabited. However, the demographic changes accompanying these events such as the population TMRCAs, population Expansion time, Effective population sizes and population growth rates merit further investigation.We have investigated human male demographic history using 590 males from 51 populations in the HGDP-CEPH worldwide panel, typed with 37 Y-SNPs and 65 Y-STRs, and analyzed with the program BATWING. BATWING uses a Markov Chain Monte Carlo (MCMC) based on the coalescent theory procedure to generate a series of genealogical trees with associated parameter values consistent with the data. After equilibration, posterior estimates of these parameters can be obtained, along with their confidence intervals.In order to investigate the information about male historical demography contained in the HGDP-CEPH dataset, we first needed to explore some features of the data: whether or not the choice of Y-STRs was important, whether or not small sample sizes could be used, and which mutation rate to adopt. We found that (1) a larger number of Y-STRs have some advantages, all 65 loci should be used; (2) a sample size of four was often sufficient to provide useful information and that we did not need to omit or combine such samples; (3) for the TMRCA, Ne and Expansion Time, median values followed the order rEMR>EMR>OMR, while for growth rate the opposite order was usually seen. According to the results of three mutation rates, the rEMR provided the best combination of insights from both OMR and EMR for prior values, and the posterior times obtained were generally consistent with other datasets. The general patterns we observe show a gradient from the oldest population TMRCAs and expansion times together with the largest effective population sizes in Africa, to the youngest times and smallest effective population sizes in the Americas. These parameters are significantly negatively correlated with distance from East Africa and the patterns are consistent with most other studies of human variation and history. In contrast, growth rate showed a weaker correlation in the opposite direction. Y lineage diversity and TMRCA also decrease with distance from East Africa, supporting a model of expansion with serial founder events starting from this source. A number of individual populations diverge from these general patterns, including previously-documented examples such as recent expansions of the Yoruba in Africa, Basques in Europe and Yakut in Northern Asia. However, some unexpected demographic histories were also found, including low growth rates in the Hazara and Kalash from Pakistan, and recent expansion of the Mozabites in North Africa.In conclusion, this survey provides the most detailed view of human male demographic history thus far available. It is based on a number of simplifications, such as the demographic model in BATWING which assumes a constant size followed by exponential expansion and does not permit more complex size changes, mixing or other characteristics of real populations. Nevertheless, it appears to capture key features of human history. In both broad outline and also in many of the exceptions to the general patterns, the conclusions fit the findings from other genetic and non-genetic studies. But some unusual patterns remain unexplained and provide directions for future work.