DNA Curve

(This is an edited post of May 31, as corrected by Kent Pryor, to whom I am very grateful.)
I just call it the Fiske curve because I don’t have any other name for it. Others may have found it and named it something else. In any case the curve sets out principles worth remembering about DNA findings in Genealogy. I got the data from conversations of several people on the Internet this week.

Several people on a Rootsweb List were discussing their strange findings from DNA tests and seemed to be laying down information we could all use.
One person wrote, “the 12 marker test is of almost no value, as many unrelated individuals can match at the 12 marker level.” I suspect that many people on many Lists are finding the same result, once they have obtained information from the 12 marker studies and then, encouraged, have gone on to the next step or two. This particular subject went on to the 67 marker test and found no one related who should be related, and then found four with the same DNA on all 67 markers who were not related at all. It is information like this that led me to think about some kind of a curve that would fit these data. Admittedly the evidence is anecdotal, but the facts real and have to be dealt with.

Another person wrote, “I have 180 names on my 12 marker (tests) on Ydna on my mother’s side all different names. I have the same thing you have on the 25 and 37 marker names that are unrelated and three different ones. . . I thought DNA had gone Crazy.”

With Ydna, you are following men’s DNA which would involve few name changes. But why is it that the more markers one uses, the less useful has become the data? Why is it that more detail seems to lead to more uncertainty? That is, adding markers tends to exclude relatives. This is counter-intuitive.

It appears that the curve is saying that if you have 0 marker tests that you could be related to everybody. If you have the minimum number of markers tested, you could be related to not all, but many people. And if you have many markers tested you are related to very few people, even in your own family.
This could mean several things:

1) DNA tests are not testing what we think they are testing.
Very simply put, DNA testing may not be valid in a scientific sense. It would be interesting to combine results of thousands of tests to see how much uncertainty is introduced to established, documented lines. Perhaps DNA tests are reflecting epigenetics, a condition that is not yet proven, but which is considered possible by some experts.

2) Family names and records are not a good indicator of genuine relationships.
This is the opposite of 1 (above). Essentially, it says there is little true paternity in family lines.

3) DNA closeness can be more due to ancient cultural habits than anything else.
Before the industrial revolution, there seem to have been few travelers. That is, one seldom traveled more than seven or more miles from his home in a lifetime. The result had to be inter-marriage of cousins, and DNA tests today are simply reflecting those intermarriages. However, in America, where Swedish immigrants married Italian immigrants, the gene pool swelled and would have made an abrupt change from, say, 1800 on. This change should be apparent in some DNA studies. (I am a six foot tall, blond and blue-eyed American who is in small part American Indian).
Maybe all the above is a result of poor labeling. But I think it is telling us something that we didn’t especially want to know. And that is that our precious DNA marker tests are not doing what we wanted.

Maybe O. J. didn't kill his wife, after all.