Friedrich over at 2 Blowhards has an exegesis of Spencer Wells' Journey of Man with handy maps (via Steve Sailer).

Two major points:

1) Wells' book focuses on the Y lineage, that is, the direct male ancestry of modern humans, ergo, the title of the book. Just like Genesis focuses on the patrilineage of humanity, so does Wells' book, neglecting our foremothers.

2) An accessible but more technically oriented summation of much of Wells' work can be found in the paper The Eurasian Heartland: A continental perspective on Y-chromosome diversity.

New readers might find my my take on the book from last year interesting.

Also....

Freddy says:

The Central Asian ‘clan’ apparently followed the steppe band across Asia and into what is now Germany, thus becoming the parents of modern Europeans.

This group made a substantial contribution to the ancestry, but neglects the possible importance of "demic diffusion" in southern/eastern Europe from a source population in the Levant/Anatolia, as well as isolation of European populations during the last glacial maxima into peripheral regions (Iberia, Ukraine, etc.). There is a reference to the Neolithic migration later, but If Freddy had limited the generalization to Swedes or Finns, I would probably not nitpick.

Also:

Members of the European Clan speaking PIE (proto-Indo-European) and having developed a horse-based (chariot) culture expand eastwards across Russia, move into Iran and ultimately invade India. Genetics suggests that this was accomplished with relatively small numbers although the cultural impacts were obviously great.

Well, the genetic evidence here is mixed, my personal opinion is that it is so confused people should not say much about it without great qualification and ass-covering, but Wells has actually offered some of the highest values of "Indo-European ancestry" that I have seen. Here from the paper I have cited:

The current distribution of the M17 haplotype is likely to represent traces of an ancient population migration originating in southern Russia/Ukraine, where M17 is found at high frequency (>50%). It is possible that the domestication of the horse in this region around 3,000 B.C. may have driven the migration (27). The distribution and age of M17 in Europe (17) and Central/Southern Asia is consistent with the inferred movements of these people, who left a clear pattern of archaeological remains known as the Kurgan culture, and are thought to have spoken an early Indo-European language (27, 28, 29). The decrease in frequency eastward across Siberia to the Altai-Sayan mountains (represented by the Tuvinian population) and Mongolia, and southward into India, overlaps exactly with the inferred migrations of the Indo-Iranians during the period 3,000 to 1,000 B.C. (27). It is worth noting that the Indo-European-speaking Sourashtrans, a population from Tamil Nadu in southern India, have a much higher frequency of M17 than their Dravidian-speaking neighbors, the Yadhavas and Kallars (39% vs. 13% and 4%, respectively), adding to the evidence that M17 is a diagnostic Indo-Iranian marker.

See here for more. Here is Spencer being interviewed by an Indian website:

Some people say Aryans are the original inhabitants of India. What is your view on this theory?

The Aryans came from outside India. We actually have genetic evidence for that. Very clear genetic evidence from a marker that arose on the southern steppes of Russia and the Ukraine around 5,000 to 10,000 years ago. And it subsequently spread to the east and south through Central Asia reaching India. It is on the higher frequency in the Indo-European speakers, the people who claim they are descendants of the Aryans, the Hindi speakers, the Bengalis, the other groups. Then it is at a lower frequency in the Dravidians. But there is clear evidence that there was a heavy migration from the steppes down towards India.

I think Spencer over-interprets the Y data here, but that's just me.