This diagram shows the human family tree as traced through the male lines,
using DNA markers on the Y chromosome.
The "Y" on the left-hand side indicates the "Adam"
from whom all of today's men's Y chromosomes descend.
The haplogroups' letter names are indicated down the right-hand side.
It comes from a paper by Mark Jobling and Chris Tyler-Smith,
published in Nature, August 2003, pp. 598-612.
You can read the article and see this diagram more clearly
in an Adobe Acrobat .pdf file by following this link,
courtesy of Family Tree DNA:
The Human Y-Chromosome: An Evolutionary Marker Comes of Age