DNA Update: 23andMe

A new feature at 23andMe is the ability to compare matches to one another, as long as they are "sharing genomes" with you.  I compared my father's 250+ matches.  (Took about eight weeks.)  Most matches matched a few others, usually with a very tiny segment.

In the above graph, my father (David) shares genetic material with all three of these people, though not on the same chromosome.  This could indicate a shared ancestry among all four of them.

In this graph, David matches all three of these people on the same area of Chromosome 12.
The limit of this DNA testing is that you are not told which side of the chromosome holds the match.
In other words, you have 23 PAIRS of chromosomes; one side from your mother, the other from your father.
All three people could match on the side from David's father, or from his mother, or one is on the maternal side, the other two on the paternal side.  We do not know from this comparison alone.

The new ability to compare matches against one another enables us to see that C. W. matches N. P, but not R. M.

In addition, N. P. does not match R. M.
From this, we can proceed with the hypothesis that N. P. and C. W. match David on one side of the family, while R. M. matches on the other.  We just have not figured out which one is which (yet).