WEBVTT 00:00:00.000 --> 00:00:03.259 Have you ever taken one of those commercial DNA 00:00:03.259 --> 00:00:05.700 tests? Oh, right. The ones where you just spit 00:00:05.700 --> 00:00:07.900 in a tube and drop it in the mail. Exactly. And 00:00:07.900 --> 00:00:09.859 then a few weeks later, you get this beautiful 00:00:09.859 --> 00:00:11.939 digital interface telling you where your ancestors 00:00:11.939 --> 00:00:13.660 came from. And it gives you all the specific 00:00:13.660 --> 00:00:17.000 genetic markers you carry. Yeah. But if you pause 00:00:17.000 --> 00:00:20.480 and really look at that data, a massive question 00:00:20.480 --> 00:00:22.960 emerges. Right. When a testing company tells 00:00:22.960 --> 00:00:27.519 you that your DNA... has certain markers or specific 00:00:27.519 --> 00:00:30.519 deviations, what exactly are they comparing your 00:00:30.519 --> 00:00:33.179 DNA against? That is the big question. What is 00:00:33.179 --> 00:00:36.520 the standard baseline for a human being? Establishing 00:00:36.520 --> 00:00:39.079 that baseline is actually one of the most crucial 00:00:39.079 --> 00:00:41.340 and, ironically, one of the most complicated 00:00:41.340 --> 00:00:44.020 endeavors in modern genetics. Because you need 00:00:44.020 --> 00:00:46.359 something to compare it to. Exactly. Without 00:00:46.359 --> 00:00:48.679 a fixed point of reference, analyzing millions 00:00:48.679 --> 00:00:51.700 of base pairs of DNA across billions of people 00:00:51.700 --> 00:00:54.420 is impossible. You need a universal map. And 00:00:54.420 --> 00:00:57.590 every map needs a starting point. Right. But 00:00:57.590 --> 00:01:00.170 how the scientific community chose that starting 00:01:00.170 --> 00:01:02.429 point and what it actually looks like under the 00:01:02.429 --> 00:01:04.829 microscope, well, it reveals a lot about how 00:01:04.829 --> 00:01:07.290 science actually progresses. Okay, let's unpack 00:01:07.290 --> 00:01:09.790 this. We are doing a deep dive today into the 00:01:09.790 --> 00:01:13.250 fascinating, slightly flawed, and constantly 00:01:13.250 --> 00:01:16.269 evolving yardstick that scientists use to map 00:01:16.269 --> 00:01:19.209 human ancestry. Specifically, we're looking at 00:01:19.209 --> 00:01:23.310 human mitochondrial DNA, or mtDNA. And exploring 00:01:23.310 --> 00:01:25.290 the Wikipedia article in the Cambridge Reference 00:01:25.290 --> 00:01:27.670 Sequence. Let's go back to the origin of this 00:01:27.670 --> 00:01:30.230 blueprint, which is a story of incredible ambition, 00:01:30.450 --> 00:01:33.590 but also a rather notorious laboratory blunder. 00:01:33.650 --> 00:01:35.430 To understand the origin, we have to travel back 00:01:35.430 --> 00:01:37.849 to the 1970s. A completely different era for 00:01:37.849 --> 00:01:40.930 genetics. Oh, absolutely. It was an era of incredible 00:01:40.930 --> 00:01:42.709 foundational work, but it was also incredibly 00:01:42.709 --> 00:01:46.930 manual. Sequencing DNA wasn't done by dropping 00:01:46.930 --> 00:01:49.810 a sample into some automated machine that spits 00:01:49.810 --> 00:01:51.790 out data in 10 minutes. Right, they had to do 00:01:51.790 --> 00:01:54.569 it by hand. It involved pouring physical gels, 00:01:54.709 --> 00:01:57.950 using radioactive tags, and painstakingly reading 00:01:57.950 --> 00:02:01.310 bands off X -ray films. At the University of 00:02:01.310 --> 00:02:03.810 Cambridge, a group of researchers, led by Fred 00:02:03.810 --> 00:02:06.650 Sanger, took on what was a monumental task at 00:02:06.650 --> 00:02:09.069 the time. Sequencing the entire mitochondrial 00:02:09.069 --> 00:02:12.050 genome of a single human being. Yes. And it was 00:02:12.050 --> 00:02:14.580 just one person. one woman of European descent. 00:02:14.659 --> 00:02:16.719 This was one. They worked on this immense puzzle 00:02:16.719 --> 00:02:19.360 throughout the entire decade, finally publishing 00:02:19.360 --> 00:02:22.099 the complete sequence in 1981. And it was an 00:02:22.099 --> 00:02:24.039 astonishing technical achievement. It really 00:02:24.039 --> 00:02:26.439 was. And to give some scale to what they were 00:02:26.439 --> 00:02:29.080 looking at, this mitochondrial genome contained 00:02:29.080 --> 00:02:32.379 some 37 genes. Which is tiny. Right, that makes 00:02:32.379 --> 00:02:37.030 up only about... 0 .00006 % of the nuclear human 00:02:37.030 --> 00:02:40.810 genome. It's a tiny, tiny fraction of the total 00:02:40.810 --> 00:02:42.750 genetic material that makes up a human body. 00:02:42.849 --> 00:02:45.330 It is a tiny fraction, but mitochondrial DNA 00:02:45.330 --> 00:02:47.949 is uniquely useful for genealogy. Because of 00:02:47.949 --> 00:02:50.129 how it's inherited, right? Exactly. Because it's 00:02:50.129 --> 00:02:52.389 passed down strictly from mother to child, it 00:02:52.389 --> 00:02:54.949 doesn't undergo the same complex shuffling that 00:02:54.949 --> 00:02:57.449 nuclear DNA does during reproduction. So it acts 00:02:57.449 --> 00:02:59.509 as a relatively stable chronological record. 00:02:59.949 --> 00:03:02.689 Precisely. When Sanger's team published their 00:03:02.689 --> 00:03:06.469 work in 1981, they determined this complete mitochondrial 00:03:06.469 --> 00:03:11.629 sequence to be exactly 16 ,569 base pairs long. 00:03:11.810 --> 00:03:16.449 16 ,569. Yes. They essentially laid down the 00:03:16.449 --> 00:03:18.930 very first track of the genetic railroad, giving 00:03:18.930 --> 00:03:21.909 scientists everywhere a standard template. This 00:03:21.909 --> 00:03:24.069 became known as the Cambridge Reference Sequence, 00:03:24.069 --> 00:03:27.599 or CRS. And having that universal template. allowed 00:03:27.599 --> 00:03:30.099 the entire field to accelerate. It gave everyone 00:03:30.099 --> 00:03:32.580 a common language. But as technology improved, 00:03:32.960 --> 00:03:35.360 other researchers inevitably started to repeat 00:03:35.360 --> 00:03:38.039 the sequencing to verify the work or build upon 00:03:38.039 --> 00:03:40.000 it. And that is when they noticed some striking 00:03:40.000 --> 00:03:42.180 discrepancies. Between what was published in 00:03:42.180 --> 00:03:44.919 1981 and what they were actually seeing in their 00:03:44.919 --> 00:03:47.039 own labs. Right. The original published sequence 00:03:47.039 --> 00:03:49.879 was actually flawed. As other scientists dug 00:03:49.879 --> 00:03:51.919 into the data over the next decade, they uncovered 00:03:51.919 --> 00:03:55.680 11 specific errors in that initial 1981 publication. 00:03:56.099 --> 00:03:59.259 11 errors? Yes. These included incorrect assignments 00:03:59.259 --> 00:04:01.400 of single base pairs, which is somewhat expected 00:04:01.400 --> 00:04:03.580 given the manual reading of those x -ray gels 00:04:03.580 --> 00:04:05.580 we talked about. It's easy to misread a blurry 00:04:05.580 --> 00:04:08.199 band on an x -ray film. But it wasn't just a 00:04:08.199 --> 00:04:10.719 matter of misreading a gel. The most shocking 00:04:10.719 --> 00:04:13.719 part of the initial mapping effort was the physical 00:04:13.719 --> 00:04:16.519 state of the sample itself. The contamination? 00:04:16.860 --> 00:04:19.670 Yes. The researchers eventually realized that 00:04:19.670 --> 00:04:22.529 the sample wasn't purely human. Which is wild 00:04:22.529 --> 00:04:24.689 to think about now. It had been contaminated 00:04:24.689 --> 00:04:28.529 with bovine DNA and HeLa cell specimens. Contamination 00:04:28.529 --> 00:04:31.730 is the invisible enemy in any laboratory, especially 00:04:31.730 --> 00:04:34.389 in the early days of sequencing before modern 00:04:34.389 --> 00:04:37.990 clean room protocols were standardized. But cow 00:04:37.990 --> 00:04:41.050 DNA. I know, it sounds crazy. But the fact that 00:04:41.050 --> 00:04:44.310 bovine DNA and HeLa cells, which are a famously 00:04:44.310 --> 00:04:47.129 robust and aggressive line of human cells used 00:04:47.129 --> 00:04:49.750 in research globally, managed to sneak into the 00:04:49.750 --> 00:04:52.139 first complete mitochondrial... sequence is a 00:04:52.139 --> 00:04:55.279 testament to how delicate the process is. It's 00:04:55.279 --> 00:04:57.819 incredibly sensitive. But the beauty of the scientific 00:04:57.819 --> 00:05:00.720 method is that it is fundamentally a self -correcting 00:05:00.720 --> 00:05:02.800 discipline. So when they finally scrubbed the 00:05:02.800 --> 00:05:04.920 bovine and helicontamination out of the sample 00:05:04.920 --> 00:05:07.579 and corrected the manual reading errors, what 00:05:07.579 --> 00:05:09.379 did they actually have left? Did the sequence 00:05:09.379 --> 00:05:12.699 change drastically? It took until 1999 for a 00:05:12.699 --> 00:05:15.800 formal correction to be published. A group of 00:05:15.800 --> 00:05:18.509 researchers led by Andrews et al. cleaned up 00:05:18.509 --> 00:05:20.589 the sequence, and published what is known as 00:05:20.589 --> 00:05:22.910 the Revised Cambridge Reference Sequence, or 00:05:22.910 --> 00:05:26.050 the RCRS. Or Revised Version. Right. They formalized 00:05:26.050 --> 00:05:28.870 the exact structure, and in doing so, confirmed 00:05:28.870 --> 00:05:31.230 that the true length of this woman's mitochondrial 00:05:31.230 --> 00:05:35.709 genome wasn't 16 ,569 base pairs at all. It was 00:05:35.709 --> 00:05:37.850 different. It was actually one base pair shorter, 00:05:38.069 --> 00:05:42.269 16 ,568. Hold on. If they deleted a base pair 00:05:42.269 --> 00:05:44.949 from the official record, doesn't that ruin the 00:05:44.949 --> 00:05:46.990 numbering system for every single scientific 00:05:46.990 --> 00:05:50.170 paper and database published since 1981? It creates 00:05:50.170 --> 00:05:53.529 a massive logistical nightmare. By 1999, the 00:05:53.529 --> 00:05:55.550 scientific community had been using the original 00:05:55.550 --> 00:05:58.189 Cambridge reference sequence for nearly two decades. 00:05:58.230 --> 00:06:00.550 That's thousands of papers. Thousands of papers, 00:06:00.730 --> 00:06:03.529 global studies, bioinformatics databases, all 00:06:03.529 --> 00:06:06.050 built on that specific coordinate system. So 00:06:06.050 --> 00:06:08.149 if you shrink the map by one base pair early 00:06:08.149 --> 00:06:10.129 in the sequence... Every single coordinate after... 00:06:16.759 --> 00:06:19.420 Rendering years of literature instantly obsolete 00:06:19.420 --> 00:06:21.639 and incredibly confusing to cross -reference, 00:06:21.779 --> 00:06:25.339 it would be like a city deciding to renumber 00:06:25.339 --> 00:06:30.300 every single house on a massive avenue. So how 00:06:30.300 --> 00:06:32.500 do they handle that missing base pair without 00:06:32.500 --> 00:06:34.379 breaking the architecture of modern genetics? 00:06:39.339 --> 00:06:42.399 technical debt a workaround yes there was an 00:06:42.399 --> 00:06:44.540 extra base pair originally listed at position 00:06:44.540 --> 00:06:48.939 3107 in the flawed 1981 sequence it was recorded 00:06:48.939 --> 00:06:52.600 as the nucleotide c okay in the 1999 revision 00:06:52.600 --> 00:06:54.839 since they knew it wasn't actually supposed to 00:06:54.839 --> 00:06:57.000 be there they didn't just delete it and shift 00:06:57.000 --> 00:06:59.199 all the numbers down instead they changed that 00:06:59.199 --> 00:07:02.060 c to an n just a placeholder a literal phantom 00:07:02.060 --> 00:07:05.160 placeholder the n stands in for an unknown or 00:07:05.160 --> 00:07:07.920 unspecified nucleotide purely to maintain the 00:07:07.920 --> 00:07:10.899 original 1981 numbering system. That is hilarious. 00:07:11.279 --> 00:07:14.240 So the sequence goes from position 3106, skips 00:07:14.240 --> 00:07:17.480 over the phantom N at 3107, and continues right 00:07:17.480 --> 00:07:20.480 along at 3108. So the scientific community collectively 00:07:20.480 --> 00:07:22.879 agreed to live with a permanent numbering anomaly 00:07:22.879 --> 00:07:26.060 rather than rewrite 20 years of genetic literature. 00:07:26.399 --> 00:07:29.600 Exactly. Today, this revised sequence is safely 00:07:29.600 --> 00:07:32.160 deposited in the GenBank database under the accession 00:07:32.160 --> 00:07:38.670 number NC012920. NC012920. That is the official, 00:07:38.870 --> 00:07:41.769 slightly jury -rigged barcode for the baseline 00:07:41.769 --> 00:07:44.870 of human mitochondrial DNA. It is. Which brings 00:07:44.870 --> 00:07:47.290 us to how this actually affects anyone who has 00:07:47.290 --> 00:07:49.870 ever dabbed a cheek swab for a genealogical test. 00:07:50.350 --> 00:07:53.089 When you get your mtDNA results back, the lab 00:07:53.089 --> 00:07:55.170 doesn't just print out a list of your 16 ,000 00:07:55.170 --> 00:07:57.410 base pairs. No, that would be unreadable. Your 00:07:57.410 --> 00:07:59.610 results are usually reported as a list of differences 00:07:59.610 --> 00:08:01.750 from this revised Cambridge reference sequence. 00:08:02.110 --> 00:08:03.889 What's fascinating here is how that reporting 00:08:03.889 --> 00:08:06.389 method creates a deeply ingrained psychological 00:08:06.389 --> 00:08:09.490 bias. We can call it the yardstick misconception. 00:08:09.990 --> 00:08:12.410 The yardstick misconception. Yes. When someone 00:08:12.410 --> 00:08:14.589 sees a genetic report that lists their differences 00:08:14.589 --> 00:08:16.670 or mutations compared to the reference sequence, 00:08:16.949 --> 00:08:19.769 the natural instinct is to assume that the reference 00:08:19.769 --> 00:08:22.310 sequence is the original, pure, or biologically 00:08:22.310 --> 00:08:25.029 normal human blueprint. The implication is that 00:08:25.029 --> 00:08:28.490 your own DNA is a deviation from that norm. It 00:08:28.490 --> 00:08:30.649 makes you feel like you are the one who mutated 00:08:30.649 --> 00:08:33.159 away from the standard. Precisely. But a helpful 00:08:33.159 --> 00:08:36.179 way to reframe the RCRS is to think of it like 00:08:36.179 --> 00:08:38.879 the prime meridian. The prime meridian runs right 00:08:38.879 --> 00:08:41.299 through Greenwich, England. Right. But there 00:08:41.299 --> 00:08:43.899 is nothing geologically zero about Greenwich. 00:08:43.980 --> 00:08:46.580 It's just an arbitrary reference point that mapmakers 00:08:46.580 --> 00:08:48.779 agreed upon so everyone could navigate. If you 00:08:48.779 --> 00:08:51.750 live at 40 degrees west. You aren't deviating 00:08:51.750 --> 00:08:53.950 from a perfect location. You're just located 00:08:53.950 --> 00:08:56.529 somewhere else relative to that agreed upon pin 00:08:56.529 --> 00:08:58.309 on the map. The Cambridge reference sequence 00:08:58.309 --> 00:09:01.230 functions in the exact same way. It is purely 00:09:01.230 --> 00:09:03.789 a reference sequence, not a record of the earliest 00:09:03.789 --> 00:09:06.470 human empty DNA. It is not the biological center 00:09:06.470 --> 00:09:09.299 of humanity. Far from it. Geneticists know exactly 00:09:09.299 --> 00:09:11.980 where it sits on the human family tree. The reference 00:09:11.980 --> 00:09:15.360 sequence belongs to a very specific modern lineage 00:09:15.360 --> 00:09:19.820 known as macro -European haplogroup H2A2A1. Wait, 00:09:19.919 --> 00:09:21.919 so when a testing company tells me I have a mutation, 00:09:22.139 --> 00:09:24.379 I haven't necessarily deviated from the human 00:09:24.379 --> 00:09:26.960 standard? I'm just different from this one specific 00:09:26.960 --> 00:09:29.899 European woman from the 1970s? That is the core 00:09:29.899 --> 00:09:32.240 of the misconception. A difference between your 00:09:32.240 --> 00:09:34.960 DNA and the CRS doesn't automatically mean you 00:09:34.960 --> 00:09:38.000 carry a rare mutation. The mutation might have 00:09:38.000 --> 00:09:40.360 actually occurred in the lineage of the Cambridge 00:09:40.360 --> 00:09:42.799 sequence itself. Oh, wow. In fact, the baseline 00:09:42.799 --> 00:09:45.259 we use for all of humanity contains genetic markers 00:09:45.259 --> 00:09:47.580 that are highly unusual when you look at the 00:09:47.580 --> 00:09:49.919 broader global population. The baseline itself 00:09:49.919 --> 00:09:52.740 is unusual. Yes. Researchers have pinpointed 00:09:52.740 --> 00:09:55.679 seven distinct locations on this genetic map 00:09:55.679 --> 00:09:58.519 where our supposed standard baseline includes 00:09:58.519 --> 00:10:02.120 rare polymorphisms. Seven distinct spots where 00:10:02.120 --> 00:10:04.159 the baseline is actually the global outlier. 00:10:04.299 --> 00:10:06.470 Yes. Do we know which ones? We do. These are 00:10:06.470 --> 00:10:10.129 specific positions like 263A, the cluster from 00:10:10.129 --> 00:10:16.269 311C to 315C, 750A, 1438A, 4769A, 03860A, and 00:10:16.269 --> 00:10:20.000 15326A. So a polymorphism is essentially a genetic 00:10:20.000 --> 00:10:22.179 variation. Correct. The fact that the universal 00:10:22.179 --> 00:10:24.580 yardstick contains seven rare variations means 00:10:24.580 --> 00:10:27.179 that for vast swaths of the global population, 00:10:27.440 --> 00:10:30.460 comparing their DNA to the CRS involves documenting 00:10:30.460 --> 00:10:32.259 differences that are actually just their own 00:10:32.259 --> 00:10:34.720 DNA being entirely normal. Exactly. While the 00:10:34.720 --> 00:10:37.340 Cambridge sequence is the odd one out. That realization 00:10:37.340 --> 00:10:40.000 seems like it would force researchers to rethink 00:10:40.000 --> 00:10:43.419 how we compare DNA globally. If you are studying 00:10:43.419 --> 00:10:46.480 populations in Africa or Asia, comparing their 00:10:46.480 --> 00:10:51.019 DNA to a European haplogroup, H2A2A1 sequence 00:10:51.019 --> 00:10:53.639 from Cambridge isn't just arbitrary, it could 00:10:53.639 --> 00:10:56.240 be analytically inefficient. It is. If the Cambridge 00:10:56.240 --> 00:10:58.860 sequence is just one pin on the map, why not 00:10:58.860 --> 00:11:01.320 make others? Well, the scientific community did 00:11:01.320 --> 00:11:03.720 attempt to diversify the baseline. Because the 00:11:03.720 --> 00:11:06.620 CRS is based on that single European individual, 00:11:07.019 --> 00:11:09.279 researchers began using alternative reference 00:11:09.279 --> 00:11:11.700 sequences. What were some of the alternatives? 00:11:12.059 --> 00:11:15.000 One notable example is the Yoruba reference sequence, 00:11:15.259 --> 00:11:18.120 representing the mitochondrial genome of an African 00:11:18.120 --> 00:11:20.559 individual. And because it's a different person 00:11:20.559 --> 00:11:22.580 from an entirely different lineage, the map looks 00:11:22.580 --> 00:11:25.039 different. Yes. The Yoruba sequence has a length 00:11:25.039 --> 00:11:29.539 of 16 ,571 base pairs, which is three base pairs 00:11:29.539 --> 00:11:32.299 longer than the revised Cambridge sequence. And 00:11:32.299 --> 00:11:34.870 scientists didn't stop there. They've also utilized 00:11:34.870 --> 00:11:37.669 an African Uganda sequence, a Swedish sequence, 00:11:37.889 --> 00:11:40.389 and a Japese sequence as alternative baselines. 00:11:40.570 --> 00:11:42.690 The intention behind localizing the reference 00:11:42.690 --> 00:11:45.629 points was good, but it created a massive fragmentation 00:11:45.629 --> 00:11:49.610 problem. Too many maps. Exactly. Having multiple 00:11:49.610 --> 00:11:52.309 different yardsticks, each with its own unique 00:11:52.309 --> 00:11:54.850 length and completely different numbering system, 00:11:55.070 --> 00:11:57.850 fractures the research landscape. You lose the 00:11:57.850 --> 00:11:59.789 universal language that the original Cambridge 00:11:59.789 --> 00:12:02.460 sequence provided. Even with its flaws and its 00:12:02.460 --> 00:12:06.179 phantom placeholder at 3107, the CRS allowed 00:12:06.179 --> 00:12:08.620 a researcher in Tokyo to perfectly understand 00:12:08.620 --> 00:12:11.039 a paper published by a researcher in London. 00:12:11.259 --> 00:12:13.980 Here's where it gets really interesting. In 2012, 00:12:14.299 --> 00:12:18.179 a group of scientists, led by Behar et al., published 00:12:18.179 --> 00:12:21.419 a paper proposing a massive philosophical shift 00:12:21.419 --> 00:12:23.759 in how genetics handles this mapping problem. 00:12:23.980 --> 00:12:26.039 They called it a Copernican reassessment of the 00:12:26.039 --> 00:12:29.190 human mitochondrial DNA tree. They proposed throwing 00:12:29.190 --> 00:12:31.350 out the revised Cambridge reference sequence 00:12:31.350 --> 00:12:33.649 as the standard and replacing it with something 00:12:33.649 --> 00:12:36.850 called the RSRS. That Copernican analogy is perfect. 00:12:37.049 --> 00:12:39.529 Before Copernicus, astronomers believed the Earth 00:12:39.529 --> 00:12:41.629 was the center of the universe, and all the math 00:12:41.629 --> 00:12:44.269 used to track the planets was incredibly convoluted 00:12:44.269 --> 00:12:45.950 because it was based on an arbitrary starting 00:12:45.950 --> 00:12:48.019 point. Right, trying to make the math fit the 00:12:48.019 --> 00:12:51.100 wrong center. Behar, et al., argued that using 00:12:51.100 --> 00:12:53.960 a modern human, whether from Cambridge, the Yoruba 00:12:53.960 --> 00:12:56.840 population, or Japan, as the center of the genetic 00:12:56.840 --> 00:13:00.340 universe was equally flawed. The RSRS, which 00:13:00.340 --> 00:13:02.940 stands for the Reconstructed Sapiens Reference 00:13:02.940 --> 00:13:06.440 Sequence, completely changes the paradigm. So 00:13:06.440 --> 00:13:08.360 instead of picking another modern person, what 00:13:08.360 --> 00:13:11.799 does the RSRS actually use as its baseline? It 00:13:11.799 --> 00:13:14.580 relies on a theoretical model. The RSRS represents 00:13:14.580 --> 00:13:18.100 the hypothetical ancestral genome of mitochondrial 00:13:18.100 --> 00:13:21.539 Eve. Yes, the theoretical root from which all 00:13:21.539 --> 00:13:24.480 currently known human mitochondria descend. That 00:13:24.480 --> 00:13:27.139 is a fundamental shift in perspective. Instead 00:13:27.139 --> 00:13:29.080 of picking a leaf on the outside of the human 00:13:29.080 --> 00:13:31.080 family tree and comparing all the other leaves 00:13:31.080 --> 00:13:33.419 to it, they mathematically work their way backward. 00:13:33.840 --> 00:13:35.879 Down the branches. All the way to the root of 00:13:35.879 --> 00:13:38.600 the tree. They reconstructed what the DNA of 00:13:38.600 --> 00:13:40.919 our most recent common matrilineal ancestor would 00:13:40.919 --> 00:13:43.299 have looked like. From an evolutionary and analytical 00:13:43.299 --> 00:13:46.259 standpoint, it is a vastly more elegant approach. 00:13:46.759 --> 00:13:49.899 If we connect this to the bigger picture. Using 00:13:49.899 --> 00:13:52.980 the ancestral root as the baseline is incredibly 00:13:52.980 --> 00:13:55.820 useful for comparing the changes across different 00:13:55.820 --> 00:13:57.899 haplogroups. Because you have a true starting 00:13:57.899 --> 00:14:00.539 point. Yes. When you measure differences from 00:14:00.539 --> 00:14:03.539 the RSRS, you are measuring the actual evolutionary 00:14:03.539 --> 00:14:06.519 path of mutations as they occurred chronologically 00:14:06.519 --> 00:14:08.919 over human history. You are tracking the journey 00:14:08.919 --> 00:14:12.000 from the root to the leaf, rather than just calculating 00:14:12.000 --> 00:14:14.399 the lateral distance between two modern leaves. 00:14:14.720 --> 00:14:17.240 It makes tracing the lineage much clearer. It 00:14:17.240 --> 00:14:19.840 makes total sense conceptually. But jumping back 00:14:19.840 --> 00:14:21.700 to the logistical problem we talked about earlier, 00:14:21.919 --> 00:14:24.779 if you change the baseline entirely to a reconstructed 00:14:24.779 --> 00:14:28.080 ancestor, doesn't that break all the bioinformatics 00:14:28.080 --> 00:14:30.799 databases again? That was the brilliance of the 00:14:30.799 --> 00:14:34.139 Behar et al. proposal. The RSRS actually keeps 00:14:34.139 --> 00:14:36.820 the exact same numbering system as the old Cambridge 00:14:36.820 --> 00:14:39.879 sequence. Oh, really? Yes. They deliberately 00:14:39.879 --> 00:14:42.700 maintain the legacy framework to ensure stability 00:14:42.700 --> 00:14:45.679 in the global databases, even while fundamentally 00:14:45.679 --> 00:14:47.840 changing what the sequence represents at its 00:14:47.840 --> 00:14:50.610 core. A structural workaround to save the databases. 00:14:50.970 --> 00:14:53.809 Exactly. But a paradigm shift like moving from 00:14:53.809 --> 00:14:58.110 a tangible European woman to a theoretical mitochondrial 00:14:58.110 --> 00:15:01.730 Eve probably wasn't embraced overnight. It absolutely 00:15:01.730 --> 00:15:05.289 sparked an ongoing debate. In 2014, a group led 00:15:05.289 --> 00:15:08.629 by Bandelt et al. published a paper pushing back 00:15:08.629 --> 00:15:11.809 against the RSRS, arguing strongly to keep using 00:15:11.809 --> 00:15:14.049 the revised Cambridge sequence. What was their 00:15:14.049 --> 00:15:16.149 reasoning? They made the case for standardizing 00:15:16.149 --> 00:15:19.690 notation around the physical known entity. It 00:15:19.690 --> 00:15:21.850 seems like a debate between practicality and 00:15:21.850 --> 00:15:25.850 theoretical purity. The RCRS is a tangible, physical 00:15:25.850 --> 00:15:28.470 sequence. We know it works as a comparative tool, 00:15:28.629 --> 00:15:31.169 despite the cow DNA history and the phantom N. 00:15:31.480 --> 00:15:33.580 Right. The RSRS is intellectually satisfying 00:15:33.580 --> 00:15:35.980 and evolutionarily accurate, but it remains a 00:15:35.980 --> 00:15:38.620 reconstructed theoretical sequence. It is a model, 00:15:38.720 --> 00:15:40.519 ultimately. So where does that leave the testing 00:15:40.519 --> 00:15:42.740 companies today? Do they use the quirky European 00:15:42.740 --> 00:15:45.980 yardstick or the reconstructed ghost of mitochondrial 00:15:45.980 --> 00:15:48.620 Eve? Commercial companies like Family Tree DNA 00:15:48.620 --> 00:15:50.960 have taken a very pragmatic approach. What do 00:15:50.960 --> 00:15:53.799 they do? They decided not to choose. They now 00:15:53.799 --> 00:15:56.940 report mtDNA results for both the RCRS and the 00:15:56.940 --> 00:15:59.639 RSRS. That's smart. They cover all the bases, 00:15:59.980 --> 00:16:02.259 providing your genetic differences compared to 00:16:02.259 --> 00:16:04.940 both the historical modern standard and the ancient 00:16:04.940 --> 00:16:08.000 evolutionary route. It allows users to view their 00:16:08.000 --> 00:16:11.159 genetics through multiple lenses. So what does 00:16:11.159 --> 00:16:13.639 this all mean? We started this deep dive looking 00:16:13.639 --> 00:16:16.539 at a reference sequence, but we found a wild 00:16:16.539 --> 00:16:19.320 timeline of human endeavor. It really is wild. 00:16:19.850 --> 00:16:22.070 The foundation of modern genetic genealogy started 00:16:22.070 --> 00:16:25.269 in the 1970s with a monumental effort to sequence 00:16:25.269 --> 00:16:28.450 one single woman's DNA. That sample survived 00:16:28.450 --> 00:16:31.490 contamination with bovine and HeLa cells. It 00:16:31.490 --> 00:16:34.110 had to be painstakingly revised. It required 00:16:34.110 --> 00:16:36.350 a phantom placeholder just to keep the world's 00:16:36.350 --> 00:16:38.649 databases from breaking. And it turned out to 00:16:38.649 --> 00:16:40.850 contain rare mutations of its own. And despite 00:16:40.850 --> 00:16:43.070 all that, it built the modern genetic landscape. 00:16:43.250 --> 00:16:46.490 It evolved into a standardized map. And now it 00:16:46.490 --> 00:16:48.509 is shifting toward a theoretical reconstruction 00:16:48.509 --> 00:16:51.429 of the mother of all modern human lineages. It 00:16:51.429 --> 00:16:53.350 is a remarkable narrative. I think the most important 00:16:53.350 --> 00:16:55.350 takeaway for you listening to this is about the 00:16:55.350 --> 00:16:57.899 nature of scientific truth. How so? Every time 00:16:57.899 --> 00:17:00.299 you read a medical claim or look at a genetic 00:17:00.299 --> 00:17:02.759 test result or hear about a biological standard, 00:17:02.960 --> 00:17:05.099 it is essential to remember that the baseline 00:17:05.099 --> 00:17:07.619 of normal is a human construct. It's an agreed 00:17:07.619 --> 00:17:10.500 -upon point. Yes. It is a tool we build to help 00:17:10.500 --> 00:17:13.519 us understand a chaotic universe. And like all 00:17:13.519 --> 00:17:16.519 tools, it is subject to revision, to the realities 00:17:16.519 --> 00:17:19.980 of laboratory limitations, and to rigorous, ongoing 00:17:19.980 --> 00:17:23.670 debate. The yardstick we use to measure humanity 00:17:23.670 --> 00:17:25.890 is always evolving alongside our understanding 00:17:25.890 --> 00:17:29.210 of ourselves. It completely changes how you view 00:17:29.210 --> 00:17:32.410 a simple pie chart or a list of genetic markers. 00:17:32.769 --> 00:17:35.029 You aren't just looking at your history. You're 00:17:35.029 --> 00:17:36.509 looking at your history filtered through the 00:17:36.509 --> 00:17:39.390 lens of a highly specific, passionately debated, 00:17:39.490 --> 00:17:42.470 and ever -changing scientific map. Which leaves 00:17:42.470 --> 00:17:44.549 us with a fascinating question to consider as 00:17:44.549 --> 00:17:46.650 we wrap up our exploration of this baseline. 00:17:46.990 --> 00:17:49.440 Let's hear it. If our ultimate genetic reference 00:17:49.440 --> 00:17:52.400 point is actively shifting from a tangible physical 00:17:52.400 --> 00:17:54.380 sample like that original Cambridge sequence 00:17:54.380 --> 00:17:57.940 to a reconstructed model of the past like the 00:17:57.940 --> 00:18:00.960 RSRS of mitochondrial Eve, how might our entire 00:18:00.960 --> 00:18:03.140 understanding of human history and our evolutionary 00:18:03.140 --> 00:18:06.019 relationships shift if scientists 50 years from 00:18:06.019 --> 00:18:08.339 now discover that our theoretical reconstruction 00:18:08.339 --> 00:18:11.420 of Eve was slightly off? That is a haunting thought. 00:18:11.619 --> 00:18:13.660 When the foundation of your map is a theoretical 00:18:13.660 --> 00:18:16.200 ghost, what happens when the ghost changes shape?