This is one of the most common complaints or questions I see in various social media groups, mostly Facebook, although it sometimes crops on Twitter.
The usual explanation, by a very large margin, is the science isn’t there yet. That’s partly true, but ignores two (2) other key points that I rarely see mentioned.
First, you don’t inherit exactly half of a parent’s ethnicity. Also, some big experts totally ignore this and tell you to double your ethnicity to get your parents’ ethnicity if they won’t or can’t test. That’s bad advice. All you have to do is look at how many times siblings share different ethnic percentages from their brothers and/or sisters. Using that logic, my sister and two (2) brothers would create three (3) other sets of ethnic results for my parents in addition to mine if I went that route. You can inherit anywhere from none to all of a parent’s specific ethnic group. It may hover around 50%, but I have seen enough where it was nowhere near the 50% mark.
Second, using myself as an example, I have a fairly large amount of paper trail British (English if you prefer) ancestry. However, I rarely get anywhere close to the amount I should based on my paper trail estimates. Why? Because everybody and their cousin in much of Europe invaded the United Kingdom (U. K.) at some point. Go to YouTube and watch this video: History of Europe – 6013 years in 3 minutes https://www.youtube.com/watch?v=uxDyJ_6N-6A. What you will see is how the borders move back and forth over the 6,000+ years. Each of the groups left DNA behind in each area it showed up, be it through peaceful or not so peaceful means. That doesn’t include cases of peaceful migration where displaced ethnic groups were relocated to other areas.
There’s a lot of non-British/English DNA in the U. K. because so many other ethnic groups left some of their DNA around. Also, for the U. K., people often stayed in the same area for long periods so whatever “foreign” DNA was added, stayed mingled in those areas. This meant it wasn’t washed out like it would be in other areas where people moved around a lot, be it by choice or by a conquering ethnic group who displaced them.
Again, using myself for an example. Suppose I fell in love with an Asian woman (Chinese or Japanese), got married and she bore me a son. I chose a son because the son would inherit my Y-DNA. Suppose my son and the next ten (10) generations all produce at least one son. Next, my son and all of patrilineal descendants only marry Asian (Chinese or Japanese) women. The odds of me being known as Generation 1 Male by that time are pretty low. Next, the male at the bottom of the patrilineal descendant chain (Generation Last Male) tests. He’s probably going to have little if any autosomal DNA (auDNA) indicating non-Asian DNA. Yet, his Y-DNA will be somewhere down the J1-YSC0000234 line, which is definitely not an Asian Y-DNA, at least in terms of Chinese or Japanese. If my existence wasn’t known, somebody would think an Not the Parent Expected (NPE) or Misattributed Parentage Event (MPE) had taken place. When in reality, all that happened is my place in the family tree got lost or misplaced.
Take the above example, but substitute that some of the women were European instead of all being Chinese or Japanese. Depending on how often it happened and how much of their and my European DNA passed on as to how much European DNA would show up in Generation Last Male’s DNA. He would still have the Y-DNA markers of J1-YSC0000234.
Let’s take the opposite scenario where my and Asian wife (Generation Female 1) also have a daughter and all of daughter’s matrilineal descendants for the same number of generations only marry European males. In that case, Last Generation Female would have little if any Asian DNA, but her mtDNA passed mother to daughter would be Asian mtDNA. In the same instance, the odds that Generation Female 1 is still known are very low so she has been lost or misplaced.
In all of the above cases, European and Asian DNA ethnicity would pass down and in the cases where it wasn’t being introduced back in, then it would probably be all gone or the trace amounts would be low enough to be considered noise most of the time. There are exceptions where a long strand of DNA gets passed mostly intact for generations, but we don’t know how common it is, or if it’s something that has to do with specific family lines passing the long strand down intact. Because over 14 million have tested autosomal DNA with companies like 23andMe, AncestryDNA, FamilyTree DNA (FTDNA), FindMyPastDNA, LivingDNA, MyHeritageDNA, and to a lesser degree Geno 2.0 and 2.0 Next. I haven’t seen total estimates of unique testers between the above companies, but it’s probably closer to 17 million or higher since some people only test with one (1) company where many often test at two (2) or more companies.
Addit: I didn’t include taking into account the various admixture tools that GEDmatch/Genesis offers as they are debateable as to how accurate their predictions are. And yes, I know some swear by them. You can check out my admixture results out at My GEDmatch Admixture Resultsand compare them to the results from the various DNA companies I tested with: Ignore Ethnic Results Below the Continental Level.