One of my favorite YouTubers is Jarret Ross, the GeneaVlogger. In his series "Professional Genealogist Reacts," he reviews videos on genealogy, often focusing on DNA-related topics.
In a recent episode, he discusses Marcus Gallo's video "You Don't Descend from All of Your Ancestors." The key point is that we are not genetically related to most of our ancestors, especially those many generations back. Although we inherit a limited number of unique genes, we have an exponentially vast number of ancestors. For example, if you go back 15 generations, you have 32,768 ancestors, but only 1,112 DNA segments to distribute among them. This means that only about 3% of those ancestors contribute to your DNA at that generation. As Gallo explains, with each generation, the number of DNA segments increases arithmetically, while the number of ancestors increases exponentially.
(Side note: My rule of thumb is that with every 10 generations, the number of ancestors multiplies by over 1,000. For instance, the 10th generation has over 1,000 ancestors, the 20th generation has over a million, the 30th generation has over a billion, and by the 40th generation, you have over a trillion ancestors! To put this in perspective, my potential ancestor Charlemagne, born in A.D. 748, is about 40 generations back. He would be one of about a trillion ancestors in that generation. Of course, there weren't actually a trillion people living back then, so pedigree collapse definitely played a role.)
In the video, Jarret Ross not only highlights Gallo's insights but also adds his own analysis. Both vloggers explore essential concepts like Y-DNA, mt-DNA, and pedigree collapse. Jarret also recommends several websites and tools for conducting in-depth DNA research.
It's an excellent video. You should check it out!
