in contrast, there is considerable genetic drift in west Eurasian populations because of the out-of-Africa bottleneck, which allows
admixture events to be more confidently assigned to this ancestry ... To increase our power to detect additional admixture
events, we performed analyses of combined populations. In a combined set of populations (the Tshwa, Shua, Haikom,
ǂHoan, Naro, and Taa_North) that have marginal evidence for a second, more recent admixture event, we infer two dates of
admixture: one 40 ± 2 generations ago and one 4 ± 1 generations ago (Z-score for the hypothesis that the admixture time is zero is
3.2, P = 7 × 10−4). In a combined set of two populations (the Juj’hoan_North and Gjui) that have marginal evidence for
a second, more ancient admixture event, we also infer two dates of admixture (SI Appendix, Fig. S24), but with different dates
from all other samples: one 30 ± 4 generations ago (Z-score of 6.9, P = 2 × 10−12) and one 109 ± 41 generations ago (Z-score of
2.6, P = 0:005). We interpret this as suggestive evidence that the population that introduced west Eurasian ancestry to southern
Africa was itself admixed, and that this more ancient admixture happened around 110 generations ago (although the confidence
intervals here are clearly large). ... The highest levels of west Eurasian ancestry are found in Khoe–Kwadi speakers (Table 1, southern Africa), particularly the Nama, where our estimate of west Eurasian ancestry reaches 14% (although note we cannot distinguish between the impact of recent colonialism and older west Eurasian ancestry in the Nama using this method).