I have read several books by Cavalli Sforza and this graph isn't very good without the explantion and background. Most of these genetic distaces are neglibilble. I likely have this book at home so I will try to post his explanations. Some things can get dated very fast because this is such a new field
Spencer Wells, who did an excellent documentary called The Journey of Man for PBS, is a student of Sforza. He is currently heading up the Genogrpahic Project:
https://www3.nationalgeographic.com/genographic/I had my DNA tested under this program. Those looking for family tree information, do not look here because it only will give you your ancient roots. Mitochondrial DNA and Y chromosomes mutate at a set time period, therefore, you can get a decent picture at how long ago two groups of people were related and how many genetic markers they share. For instance, preliminary results seem to support the Lemba tribes "Jewishness" as there is a disportionate # of men who share the same marker as known Kohanim.
A decent laymen's intro on these matters can be found in the first half of Bryan Sykes The Seven Daughters of Eve.
