An anthropologist asks:
Now go even further back in time to the 17th or 18th century. The number of folks on average living then who could have contributed to your genetic endowment is so large (more than 1,000), and their possible genetic contribution so small (about 0.098 percent for 10 generations back), it would be smoke and mirrors to assert claims about who they were in person. In fact, most of these people left no trace of themselves in your genome.
In short, while it can be hard to get your head around the statistics involved, go back more than a few thousand years and you are genealogically related to almost everyone on Earth. Genetically speaking, however, very few of these very distant ancestors contributed something of themselves biologically to your genome.
Human races are inventions of the human mind. Substituting words like “ancestry” or “heritage” for the disreputable old term “race” may sound like progress, but it isn’t. These tests are about more than just having fun with expensive laboratory equipment. By encouraging us to see ourselves as a mix of allegedly different ethnic groups, populations, races, and the like rather than as a mix of genes, commercial DNA tests may lend seeming scientific credence to ideas that by now ought to have been long dead and buried—enduring assumptions about human diversity that have ripped the world apart for far too long. John Edward Terrell, “Ancestry Tests Pose a Threat to Our Social Fabric” at Sapiens
He recommends getting to know the neighbors instead of hoping to hear that our ancestors were royalty.
See also: Now that’s different: Identical twins, one in space, have different DNA?
Identical twins show epigenetic similarity as well. Then what about the famous “twin studies”?
Identical twins are not really identical (on Earth) and tend to diverge as they go through life. See also: There’s a gene for that… or is there?