DNA analysis has been very helpful to archaeology, and is now widely available from a number of providers as a relatively affordable test. The companies all select and measure data in different ways.
This has led to a great deal of confusion, for example, in how maps of haplogroup types are drawn.
Two maps of the same haplogroup are compared below.
You might notice similarities and differences between the two. This is simply based on where the program that drew each map has been told to select data divisions. In addition, knowledge changes over time, so be sure the map you are looking at was recently produced.
Also please look at who has produced the information, or the map, you're studying. One of the maps above has been created by a frankly self-styled expert whose actually academic credentials are not apparent. The other has been drawn up by a group of researchers and published with full citation of sources, methods and peer reviews. I'll let you figure which is which (check the links the images lead to).
Finally, 'the map is not the territory'. Even the most informed scientist can draw maps that prove to be just plain wrong. They should be treated as a visual guide that engages you to think more - not a definition of reality.
One well-known company was pleased to tell me I have a lot of 'Scandinavian DNA' and included many cut-and-pasted paragraphs about the Vikings, plus a nice coloured picture of a Viking longboat. Hurray, I am largely Erik the Red!
Pinning DNA haplogroups to historic events is dangerous territory.
Vikings were part-time seasonal robbers, not an ethnic group.
My 'Scandinavian DNA' may have entered that geographical zone at any time in the last 13,000 years, and it may be the DNA of a far older, more south- easterly group who re-populated the area after the ice retreat.
It may have entered my family tree via a friendly merchant seaman round Salford Docks in the early 20th century.
You can pay thousands of pounds and get a detailed forensic genetic family tree, with commentary, and it can still be subject to change as new knowledge emerges. Enjoy your DNA history but don't hang too much expectation on it!
But maybe the same old lady objects vociferously at a council planning meeting, and is asked to leave. She maybe has a little weep on the way out and drops her kleenex into the waste-bin. That can be collected forensically. Her DNA might be logged on a police system as a violent dissident.
You get the picture. 'Quis custodiat ipsos custodes' - who is guarding the actual guardians?
We have been lucky in the UK to have had relatively benign, balanced and democratic government for a long time. I would not like to think of the reach of an unfriendly dictatorship that had mass access to population DNA.
Paranoia - or are they really out to get me?
Warnings about DNA 'libraries' appear in the UK to be led by Genewatch. You may find this in itself problematical, as Genewatch is closely aligned with the green movement, which is also closely allied to radical activism.