A very exciting new paper has just been published in Genome Research on 456 full sequence Y-chromosomes from around the world. The authors date the MRCA of Y-chromosomes ("Y chromosome Adam") to 254 (95% CI 192–307) kya, find coalescences of major non-African haplogroups to 47–52 kya (which clearly corresponds to the Upper Paleolithic revolution), but also infer a second bottleneck that occurred in the last 10 thousand years.
The contrast (left) between mtDNA (red) and Y-chromosome (yellow) coalescences is quite noticeable. The little "dip" in the yellow curve in many regions on the right of the various regional plots corresponds to a the second bottleneck event (that was really not "one" event, but rather shows that many modern men descend from a small number of "patriarchs" of the Neolithic and Bronze Age worlds. The "when" of the dip is important:..http://dienekes.blogspot.com/2015/03/bottleneck-in-human-y-chromosomes-in.html