Dienekes Pontikos has a note argueing that the human race is accummulating mutations at the maximum possible rate and consequently it is changing at backbreaking velocity. Very well written and clear.
...in population studies, scientists are likely observe (in the finite samples they collect) multiple descendants only of the most prolific of the Patriarchs. Thus, for the vast majority of the Patriarchs with few descendants, we are likely to sample no, or few of their descendants.
This means that there is an inherent observation selection effect in the types of Patriarchs we are likely to study: they are much more likely to be among the prolific ones. Coupling this observation with the knowledge that STR variance in the descendants of prolific Patriarchs accumulates near the germline mutation rate (0.69µ for the 100 most prolific ones in my experiment), we, once again, conclude that the STR variance in haplogroups likely to be made the object of scientific study accumulates near the germline mutation rate, and at the very least, faster than the evolutionary rate of Z.U.F.
Z.U.F. have also proposed two additional demographic scenaria under which a higher effective mutation rate would be observed:
A sudden jump in the size of the haplogroup after it appears
An expanding population (m>1)
Both factors seem reasonable for post-Holocene human populations. It is well known that -whatever temporary setbacks there were- mankind has overall experienced a substantial population growth in recent millennia. Thus, an expanding population seems like a fair assumption.
Moreover, it is reasonable to assume that in stratified human societies, a few males, (leaders, or conquerors), or groups of closely related males may have generated a disproportionate number of descendants in the short-term.