First, it reports the discovery of a new major clade within the Y-chromosome phylogeny which unites many previously paraphyletic E-M35* chromosomes, and charts its distribution in Africa (left).
The second claim in the study is that this new clade is associated with the spread of pastoralism into southern Africa:
Using the same mutation rate described in Fig. 1, we estimated a maximum age of 2,700 ya (ρ=0.6, n = 10) with a standard error (SE) of 1,100 y.But, this claim is another house of cards based on an assumption of an evolutionary mutation rate that is much lower than the observed germline rate. The authors cite Zhivotovsky et al. (2004) (pdf) regarding this rate, but Zhivotovsky, Underhill, and Feldman (2006) showed that such a lower effective rate is observed in a constant-sized population, where each lineage grows stochastically according to a Poisson process with parameter 1. The expected number of its descendants after g generations is 0.5g or 40 individuals after 2,000 years, a few orders of magnitude less than the real number of E-M293 bearers.
A major unresolved question is: were early instances of sheep, cows, pottery, and their pastoralist markers transmitted to southern-central Africa by demic or cultural diffusion?
Given the directionality and dating discussed previously, we conclude that eastern African individuals contributed M293 to southern African populations within the last few thousand years. The scale of this migration may have been small, minimally four male individuals
So, the evolutionary rate is totally inappropriate for the pastoralist groups in question who have grown to a much larger size than that.
For a more thorough discussion of the problems with the evolutionary rate, see my two part discussion (part I and part II). In a group that expands in size a much faster evolutionary rate is appropriate, approaching the germline rate.
The argument that E-M293 is associated with the introduction of pastoralism to southern Africa is another house of cards resting on the assumption of the slow evolutionary mutation rate.
So, while E-M293 did follow the proposed migration route, and E-M293 migrants were also pastoralists, they weren't necessarily the people who introduced pastoralism to southern Africa -- they came much later.
Related public release and blog post at the Spittoon.
PNAS Y-chromosomal evidence of a pastoralist migration through Tanzania to southern Africa
Brenna M. Henn et al.
Although geneticists have extensively debated the mode by which agriculture diffused from the Near East to Europe, they have not directly examined similar agropastoral diffusions in Africa. It is unclear, for example, whether early instances of sheep, cows, pottery, and other traits of the pastoralist package were transmitted to southern Africa by demic or cultural diffusion. Here, we report a newly discovered Y-chromosome-specific polymorphism that defines haplogroup E3b1f-M293. This polymorphism reveals the monophyletic relationship of the majority of haplotypes of a previously paraphyletic clade, E3b1-M35*, that is widespread in Africa and southern Europe. To elucidate the history of the E3b1f haplogroup, we analyzed this haplogroup in 13 populations from southern and eastern Africa. The geographic distribution of the E3b1f haplogroup, in association with the microsatellite diversity estimates for populations, is consistent with an expansion through Tanzania to southern-central Africa. The data suggest this dispersal was independent of the migration of Bantu-speaking peoples along a similar route. Instead, the phylogeography and microsatellite diversity of the E3b1f lineage correlate with the arrival of the pastoralist economy in southern Africa. Our Y-chromosomal evidence supports a demic diffusion model of pastoralism from eastern to southern Africa ≈2,000 years ago.