WEBVTT 00:00:00.000 --> 00:00:03.620 Welcome, everyone, and a very special welcome 00:00:03.620 --> 00:00:06.099 to you, the learner. Yeah, welcome to the deep 00:00:06.099 --> 00:00:08.859 dive. You know who you are. You're the person 00:00:08.859 --> 00:00:13.839 who loves to peel back the layers of how we know 00:00:13.839 --> 00:00:16.079 what we know. Right, skipping the fluff and just 00:00:16.079 --> 00:00:18.000 getting right to the core of the matter. Exactly. 00:00:18.359 --> 00:00:20.539 And today our mission on this deep dive is to 00:00:20.539 --> 00:00:24.960 unpack a single, absolutely fascinating Wikipedia 00:00:24.960 --> 00:00:27.019 article about something called the Cambridge 00:00:27.019 --> 00:00:31.359 Reference Sequence, or the CRS. It is a critical 00:00:31.359 --> 00:00:33.740 piece of scientific history. It really is. But 00:00:33.740 --> 00:00:35.700 as we comb through our source material today, 00:00:35.759 --> 00:00:37.679 we uncover a foundation that was built with a 00:00:37.679 --> 00:00:39.920 rather colorful and sometimes, I mean, really 00:00:39.920 --> 00:00:42.179 chaotic methodology. Colorful is definitely one 00:00:42.179 --> 00:00:44.280 word for it. To set this up for you, the listener, 00:00:44.420 --> 00:00:46.939 I want you to imagine something. Okay. Imagine 00:00:46.939 --> 00:00:49.719 you were trying to read a highly detailed map 00:00:49.719 --> 00:00:53.109 of human ancestry. You're tracing the lines. 00:00:53.149 --> 00:00:54.950 You're looking for the very origins of humanity. 00:00:55.130 --> 00:00:57.409 And you're relying on this big, bold, you are 00:00:57.409 --> 00:01:00.210 here marker on the map to orient yourself. Right. 00:01:00.270 --> 00:01:02.630 Now imagine finding out that the baseline marker 00:01:02.630 --> 00:01:04.689 you've been using to navigate the history of 00:01:04.689 --> 00:01:08.609 human DNA accidentally includes cow DNA. It sounds 00:01:08.609 --> 00:01:11.739 like an urban legend. Right. But it is entirely 00:01:11.739 --> 00:01:14.459 rooted in the actual history of how this sequence 00:01:14.459 --> 00:01:16.920 was developed and used by the global scientific 00:01:16.920 --> 00:01:19.599 community. It's just wild to think about. So 00:01:19.599 --> 00:01:22.340 here is our roadmap for today's deep dive. We're 00:01:22.340 --> 00:01:24.200 going to explore what the Cambridge reference 00:01:24.200 --> 00:01:27.420 sequence actually is and the immense effort it 00:01:27.420 --> 00:01:30.200 took to create it in the 1970s. And then we'll 00:01:30.200 --> 00:01:33.099 look at the absolutely fascinating lab mistakes 00:01:33.099 --> 00:01:35.879 that occurred in its original creation. Yes. 00:01:36.099 --> 00:01:39.480 And finally, we'll delve into the current. fiercely 00:01:39.480 --> 00:01:43.760 debated scientific schism over exactly how we 00:01:43.760 --> 00:01:46.560 should be tracing our mitochondrial family tree 00:01:46.560 --> 00:01:49.200 today. Okay, let's unpack this. Let's start by 00:01:49.200 --> 00:01:51.219 setting the scene and appreciating the sheer 00:01:51.219 --> 00:01:53.620 technological mountain scientists were climbing 00:01:53.620 --> 00:01:55.780 back then. Oh, absolutely. We need to go back 00:01:55.780 --> 00:01:58.920 in time to the 1970s. During this decade, a group 00:01:58.920 --> 00:02:00.599 of researchers at the University of Cambridge 00:02:00.599 --> 00:02:02.959 led by the legendary scientist Fred Sanger took 00:02:02.959 --> 00:02:05.540 on a monumental task. Right. They set out to 00:02:05.540 --> 00:02:08.340 sequence the human mitochondrial genome. Which, 00:02:08.439 --> 00:02:10.419 just to make sure we are all on the same page, 00:02:10.520 --> 00:02:13.479 is different from the main bulk of our DNA, right? 00:02:13.539 --> 00:02:17.259 The nuclear DNA. If our main DNA is the massive 00:02:17.259 --> 00:02:19.819 reference library inside the nucleus of the cell, 00:02:19.979 --> 00:02:23.860 the mitochondrial DNA is more like a tiny separate 00:02:23.860 --> 00:02:26.159 instruction manual. Down in the boiler room. 00:02:26.219 --> 00:02:28.500 Yeah, kept down in the boiler room, the mitochondria 00:02:28.500 --> 00:02:31.159 which generate power for the cell. That is a 00:02:31.159 --> 00:02:33.819 perfect way to visualize it. And the way Sanger's 00:02:33.819 --> 00:02:36.120 team built this map is crucial to everything 00:02:36.120 --> 00:02:38.419 that follows. They didn't take an average of 00:02:38.419 --> 00:02:40.599 thousands of people. No, they didn't. They sequenced 00:02:40.599 --> 00:02:43.599 the mitochondrial genome of just one single woman 00:02:43.599 --> 00:02:46.280 of European descent. Just one person. All the 00:02:46.280 --> 00:02:48.280 baseline data they gathered was from this one 00:02:48.280 --> 00:02:52.099 individual's biological material. And they labored 00:02:52.099 --> 00:02:54.219 over this throughout the 1970s, working entirely 00:02:54.219 --> 00:02:56.819 without the automated high -speed computers we 00:02:56.819 --> 00:02:58.780 have today. It's staggering to think about doing 00:02:58.780 --> 00:03:00.870 that level of genetics. sequencing manually. 00:03:01.129 --> 00:03:02.990 And they finally published their sequence in 00:03:02.990 --> 00:03:06.349 1981. It was a massive triumph of 20th century 00:03:06.349 --> 00:03:08.569 biology. The source gives us some really specific 00:03:08.569 --> 00:03:10.550 statistics on what they found too, right? In 00:03:10.550 --> 00:03:13.349 that 1981 release. It does. First, they determined 00:03:13.349 --> 00:03:15.590 that this mitochondrial sequence contains some 00:03:15.590 --> 00:03:19.550 37 genes. Just 37 genes. I mean, compared to 00:03:19.550 --> 00:03:22.460 the tens of thousands in our main genome. That 00:03:22.460 --> 00:03:25.360 is tiny. It is a vanishingly small piece of our 00:03:25.360 --> 00:03:27.960 genetic makeup. To put the scale into perspective, 00:03:28.280 --> 00:03:33.080 this mitochondrial DNA represents just 0 .0006 00:03:33.080 --> 00:03:36.699 % of the nuclear human genome. Wow. Yet because 00:03:36.699 --> 00:03:39.860 mitochondrial DNA is passed down almost exclusively 00:03:39.860 --> 00:03:43.039 from mother to child, it is an incredibly vital 00:03:43.039 --> 00:03:46.000 tool for tracing maternal ancestry. And the source 00:03:46.000 --> 00:03:48.199 also mentions the length of the sequence they 00:03:48.199 --> 00:03:50.020 mapped out. When we talk about the length of 00:03:50.020 --> 00:03:52.159 DNA, we talk about base pairs. Right, the rungs 00:03:52.159 --> 00:03:53.819 of the ladder. Yeah, the individual chemical 00:03:53.819 --> 00:03:56.639 letters that make up the DNA ladder, the S, C, 00:03:56.639 --> 00:04:00.180 S, T's and G's. The 1981 publication announced 00:04:00.180 --> 00:04:02.580 that this woman's mitochondrial sequence had 00:04:02.580 --> 00:04:06.900 a length of exactly 16 ,569 base pairs. And they 00:04:06.900 --> 00:04:08.680 published that number with great confidence. 00:04:08.939 --> 00:04:11.159 They sure did. However, the source points out 00:04:11.159 --> 00:04:13.759 a brilliant, surprising detail right from the 00:04:13.759 --> 00:04:16.600 jump. due to a mistake made during that original 00:04:16.600 --> 00:04:19.600 grueling manual sequencing process. The actual 00:04:19.600 --> 00:04:23.660 length of that specific sequence isn't 16 ,569. 00:04:23.839 --> 00:04:29.060 No, it is exactly 16 ,568 base pairs. They spent 00:04:29.060 --> 00:04:31.879 a decade mapping it by hand, and they were off 00:04:31.879 --> 00:04:34.740 by a single letter. What's fascinating here is 00:04:34.740 --> 00:04:36.839 that despite that mistake, and we will get into 00:04:36.839 --> 00:04:40.180 the more severe error shortly, this specific 00:04:40.180 --> 00:04:42.779 sequence from one single woman of European descent 00:04:42.779 --> 00:04:46.560 became the definitive baseline map for human 00:04:46.560 --> 00:04:50.019 mitochondrial genetics. For decades, it was the 00:04:50.019 --> 00:04:52.240 gold standard. It became the ultimate measuring 00:04:52.240 --> 00:04:55.180 stick for the entire globe. Right. Whenever scientists 00:04:55.180 --> 00:04:57.819 anywhere in the world wanted to look at mitochondrial 00:04:57.819 --> 00:05:01.079 DNA, they compared it to this Cambridge reference 00:05:01.079 --> 00:05:03.720 sequence. So if your DNA had... an A where the 00:05:03.720 --> 00:05:06.319 Cambridge sequence had a T, that difference was 00:05:06.319 --> 00:05:08.639 logged as a variation. And because it became 00:05:08.639 --> 00:05:11.379 the global yardstick, other laboratories naturally 00:05:11.379 --> 00:05:13.680 began using it, testing it, and applying it to 00:05:13.680 --> 00:05:16.300 their own research. The scientific method relies 00:05:16.300 --> 00:05:19.100 on replication. But when other researchers finally 00:05:19.100 --> 00:05:21.279 started to repeat the sequencing that Sanger's 00:05:21.279 --> 00:05:23.699 team had done, they didn't just find that one 00:05:23.699 --> 00:05:25.860 missing base pair. No, they found quite a bit 00:05:25.860 --> 00:05:28.930 more. The article notes that they found what 00:05:28.930 --> 00:05:31.689 it calls striking discrepancies. They started 00:05:31.689 --> 00:05:34.069 looking closely at the original sequence and 00:05:34.069 --> 00:05:37.350 realized the 1981 map had some serious topographical 00:05:37.350 --> 00:05:40.110 errors. The scientific community methodically 00:05:40.110 --> 00:05:42.810 went through the 1981 sequence and eventually 00:05:42.810 --> 00:05:46.430 identified a total of 11 specific errors in the 00:05:46.430 --> 00:05:49.230 original published data. 11 errors. And these 00:05:49.230 --> 00:05:51.629 errors took a few different forms. There were 00:05:51.629 --> 00:05:54.069 incorrect assignments of single base pairs where 00:05:54.069 --> 00:05:56.930 the original team had essentially just misidentified 00:05:56.930 --> 00:06:00.139 the nucleotide. a specific position. Right. But 00:06:00.139 --> 00:06:02.339 there were also structural issues that required 00:06:02.339 --> 00:06:04.399 correction. I'll let you take the lead on the 00:06:04.399 --> 00:06:06.500 technical side of this because the source highlights 00:06:06.500 --> 00:06:09.040 one glaring structural error that really stood 00:06:09.040 --> 00:06:11.339 out. The most notable structural error occurred 00:06:11.339 --> 00:06:14.560 at a specific position known as 3107 Bell. Okay. 00:06:14.860 --> 00:06:18.060 3107 Bell. In the original 1981 sequence, the 00:06:18.060 --> 00:06:20.339 researchers recorded an extra base pair at that 00:06:20.339 --> 00:06:23.680 spot, labeling it as a C for cytosine. But it 00:06:23.680 --> 00:06:26.680 wasn't there. Exactly. We now know that extra 00:06:26.680 --> 00:06:29.180 base pair simply didn't exist in the actual DNA. 00:06:29.439 --> 00:06:31.319 So how do they fix that without throwing off 00:06:31.319 --> 00:06:33.600 all the numbers after it? Today, in order to 00:06:33.600 --> 00:06:35.959 maintain the overall numbering system, without 00:06:35.959 --> 00:06:38.339 shifting every subsequent number down by one, 00:06:38.379 --> 00:06:40.699 that position is labeled with an N. So they essentially 00:06:40.699 --> 00:06:43.120 put an N in there as a placeholder. Precisely. 00:06:43.120 --> 00:06:46.199 It just stands for an unspecified or unknown 00:06:46.199 --> 00:06:49.370 nucleotide. basically a blank space, to make 00:06:49.370 --> 00:06:51.689 up for the fact that the original sea was a phantom 00:06:51.689 --> 00:06:54.870 letter. It acts as a structural bridge to keep 00:06:54.870 --> 00:06:57.310 the rest of the map's coordinates intact. Exactly. 00:06:57.610 --> 00:07:00.129 But the real kicker, and this is easily the most 00:07:00.129 --> 00:07:02.709 surprising revelation in the entire deep dive, 00:07:03.879 --> 00:07:06.579 The part that absolutely completely changes how 00:07:06.579 --> 00:07:09.740 you view early genetic science is why some of 00:07:09.740 --> 00:07:12.000 these 11 errors happened. It really pulls back 00:07:12.000 --> 00:07:14.360 the curtain on the lab work of that era. You'd 00:07:14.360 --> 00:07:16.379 think it was just a smudge on a photographic 00:07:16.379 --> 00:07:19.279 plate or human fatigue from staring at data. 00:07:19.420 --> 00:07:21.959 The reality is much more reflective of the gritty 00:07:21.959 --> 00:07:25.259 nature of 1970s laboratory work. The article 00:07:25.259 --> 00:07:27.540 states explicitly that some of these errors were 00:07:27.540 --> 00:07:30.300 the result of biological contamination. Contamination. 00:07:30.399 --> 00:07:32.699 The specimens used in the original sequencing 00:07:32.699 --> 00:07:35.360 were contaminated with HeLa specimens. For those 00:07:35.360 --> 00:07:37.680 who might not be familiar, HeLa cells are incredibly 00:07:37.680 --> 00:07:40.560 famous in biology. They stem from a woman named 00:07:40.560 --> 00:07:43.519 Henrietta Lacks. And they are essentially the 00:07:43.519 --> 00:07:46.959 first immortal human cell line. They are famously 00:07:46.959 --> 00:07:49.120 resilient to the point where they are notorious 00:07:49.120 --> 00:07:52.600 for floating through the air or hitching a ride 00:07:52.600 --> 00:07:55.339 on lab equipment and aggressively taking over 00:07:55.339 --> 00:07:57.720 other cultures in a laboratory. HeLa contamination 00:07:57.720 --> 00:08:00.639 is a well -documented hazard in cell biology. 00:08:01.389 --> 00:08:03.189 But the contamination of the Cambridge reference 00:08:03.189 --> 00:08:05.610 sequence didn't stop at HeLa cells. No, it did 00:08:05.610 --> 00:08:08.029 not. The original samples were also contaminated 00:08:08.029 --> 00:08:11.670 with bovine specimens. Cow DNA. There was cow 00:08:11.670 --> 00:08:14.250 DNA mixed into the baseline reference sequence 00:08:14.250 --> 00:08:16.990 for the human mitochondrial genome. It is a remarkable 00:08:16.990 --> 00:08:19.589 piece of history. It is just wild to me that 00:08:19.589 --> 00:08:22.209 for years the blueprint we used to understand 00:08:22.209 --> 00:08:25.310 human origins had a little bit of bovine genetic 00:08:25.310 --> 00:08:27.889 material mixed in by accident. It highlights 00:08:27.889 --> 00:08:30.930 a critical vulnerability in early genetics. Before 00:08:30.930 --> 00:08:33.370 the advent of modern sterile techniques, sealed 00:08:33.370 --> 00:08:35.230 environments and computational error checking 00:08:35.230 --> 00:08:38.289 researchers often used bovine serum to nourish 00:08:38.289 --> 00:08:41.330 cell cultures in the lab. And traces of that 00:08:41.330 --> 00:08:45.090 bovine material simply snuck into the final sequence. 00:08:45.269 --> 00:08:47.450 Exactly. Scientists obviously couldn't just leave 00:08:47.450 --> 00:08:49.610 it like that. You can't have a global yardstick 00:08:49.610 --> 00:08:52.049 made partly of cow. No. The scientific community 00:08:52.049 --> 00:08:55.250 recognized the need for a clean baseline. A revised 00:08:55.250 --> 00:08:58.049 version was pain. Unstakenly assembled and published 00:08:58.049 --> 00:09:02.210 in 1999 by a team led by Andrews et al. Okay. 00:09:02.269 --> 00:09:05.490 They cleaned up the 11 errors, completely removed 00:09:05.490 --> 00:09:08.289 the bovine and HeLa contamination, and published 00:09:08.289 --> 00:09:10.730 what is now known as the Revised Cambridge Reference 00:09:10.730 --> 00:09:14.230 Sequence, or the RCRS. The RCRS. And that's what 00:09:14.230 --> 00:09:16.559 scientists used today. It is. The source mentions 00:09:16.559 --> 00:09:18.120 that if someone wants to go look it up themselves, 00:09:18.360 --> 00:09:21.480 it is officially deposited in the GenBank NCBI 00:09:21.480 --> 00:09:23.940 database. Anyone can access it. You can find 00:09:23.940 --> 00:09:26.779 it under the accession number NC underscore zero 00:09:26.779 --> 00:09:30.200 one two nine two zero. That is the corrected, 00:09:30.340 --> 00:09:32.899 pristine, modern version of the original 1981 00:09:32.899 --> 00:09:35.100 sequence. But even with the corrections, they 00:09:35.100 --> 00:09:37.379 faced a massive logistical headache regarding 00:09:37.379 --> 00:09:39.740 the numbering. Because the actual length of the 00:09:39.740 --> 00:09:44.940 sequence is 16 ,568 base pairs, not the 69. originally 00:09:44.940 --> 00:09:47.340 published. Right. Plus you have issues like that 00:09:47.340 --> 00:09:50.519 Phantom C at position 3107. So what did they 00:09:50.519 --> 00:09:53.340 do? When Andrews and his team revised the sequence 00:09:53.340 --> 00:09:56.659 in 1999, they faced a difficult choice. They 00:09:56.659 --> 00:09:58.779 could renumber the entire sequence from scratch 00:09:58.779 --> 00:10:02.320 1 to 16568 to perfectly reflect the accurate 00:10:02.320 --> 00:10:05.399 physical reality of the DNA molecule. Which feels 00:10:05.399 --> 00:10:07.860 like the most scientifically pure thing to do, 00:10:07.899 --> 00:10:09.899 just wipe the slate clean and number it correctly. 00:10:10.330 --> 00:10:12.549 The problem with scientific purity is that it 00:10:12.549 --> 00:10:15.289 often collides with practical reality. Think 00:10:15.289 --> 00:10:17.629 about the context. Right. Nearly 20 years have 00:10:17.629 --> 00:10:21.470 passed. Exactly. By 1999, nearly two decades 00:10:21.470 --> 00:10:24.389 of scientific literature. Thousands of published 00:10:24.389 --> 00:10:26.850 papers and countless evolutionary studies had 00:10:26.850 --> 00:10:28.690 been anchored to the original numbering system 00:10:28.690 --> 00:10:32.009 of the 1981 CRS. Oh, wow. So if they changed 00:10:32.009 --> 00:10:33.509 all the numbers, it would be like changing the 00:10:33.509 --> 00:10:35.429 Dewey Decimal System overnight. It would have 00:10:35.429 --> 00:10:37.769 created absolute chaos in the field of genetics. 00:10:37.990 --> 00:10:40.169 Every single book, every single paper published 00:10:40.169 --> 00:10:43.149 before 1999 would suddenly have the wrong coordinates. 00:10:43.429 --> 00:10:45.450 It would render an entire generation of scientific 00:10:45.450 --> 00:10:48.509 literature incredibly difficult to read and cross 00:10:48.509 --> 00:10:50.870 -reference. Researchers would have needed a conversion 00:10:50.870 --> 00:10:54.110 chart just to read a paper from 1995. That sounds 00:10:54.110 --> 00:10:56.409 like a nightmare. So despite making the rigorous 00:10:56.409 --> 00:10:58.830 chemical corrections to the actual genetic data, 00:10:59.029 --> 00:11:01.230 the scientific community made the deliberate 00:11:01.230 --> 00:11:04.610 decision to retain the flawed original nucleotide 00:11:04.610 --> 00:11:07.649 numbering system. It's such a pragmatic human 00:11:07.649 --> 00:11:10.629 solution to a scientific problem. They kept the 00:11:10.629 --> 00:11:13.580 fandom space at 3107. just to keep the filing 00:11:13.580 --> 00:11:16.139 system intact. They did. I want to bring this 00:11:16.139 --> 00:11:18.220 directly back to you, the listener. You might 00:11:18.220 --> 00:11:20.559 be wondering how an off -by -one error from a 00:11:20.559 --> 00:11:23.779 1970s laboratory affects you today. Well, if 00:11:23.779 --> 00:11:25.980 you have ever taken a genealogical DNA test. 00:11:26.139 --> 00:11:28.179 One of those swab -your -cheek or spin -the -tube 00:11:28.179 --> 00:11:30.539 kits. Exactly, to find out your maternal ancestry. 00:11:31.259 --> 00:11:33.779 Your results are intimately tied to this story. 00:11:34.019 --> 00:11:36.860 Your personal ancestry report is a direct descendant 00:11:36.860 --> 00:11:39.720 of that 1999 revision. Because when those testing 00:11:39.720 --> 00:11:42.590 companies look at your mitochondrial DNA, They 00:11:42.590 --> 00:11:44.710 don't map out your entire sequence from scratch 00:11:44.710 --> 00:11:48.450 and hand you a microscopic list of 16 ,500 plus 00:11:48.450 --> 00:11:51.210 letters. No. Instead, your results are reported 00:11:51.210 --> 00:11:54.129 simply as the differences between your DNA and 00:11:54.129 --> 00:11:57.210 this revised Cambridge reference sequence. You 00:11:57.210 --> 00:11:59.970 are literally being compared to that one European 00:11:59.970 --> 00:12:03.230 woman from the 1970s. If we connect this to the 00:12:03.230 --> 00:12:05.950 bigger picture, it is vital to remember what 00:12:05.950 --> 00:12:09.090 the CRS actually is and, more importantly, what 00:12:09.090 --> 00:12:11.629 it is not. Right. It is just a reference sequence. 00:12:11.769 --> 00:12:13.870 It is a yardstick. It is not a record of the 00:12:13.870 --> 00:12:16.710 earliest human mitochondrial DNA. It doesn't 00:12:16.710 --> 00:12:19.289 represent the origin point of human... or some 00:12:19.289 --> 00:12:22.889 perfect average human specimen? Not at all. It's 00:12:22.889 --> 00:12:24.850 an arbitrary starting line that we only use because 00:12:24.850 --> 00:12:26.950 she happened to be the first person sequenced. 00:12:27.149 --> 00:12:29.350 To be precise, the reference sequence belongs 00:12:29.350 --> 00:12:32.429 to a specific modern haplogroup. Which is essentially 00:12:32.429 --> 00:12:34.590 a major modern branch on the human evolutionary 00:12:34.590 --> 00:12:38.129 family tree. Yes, known as H2A2A1. It's a macro 00:12:38.129 --> 00:12:41.009 -European lineage. So what does this all mean? 00:12:41.149 --> 00:12:43.730 When the DNA test says, A, your DNA is different 00:12:43.730 --> 00:12:45.389 from the reference sequence at this specific 00:12:45.389 --> 00:12:48.240 spot, what does that actually tell us? us about 00:12:48.240 --> 00:12:50.500 our own genetics. It tells us about a genetic 00:12:50.500 --> 00:12:53.100 mutation, but we have to be incredibly careful 00:12:53.100 --> 00:12:55.919 about our assumptions. When a difference is found 00:12:55.919 --> 00:12:59.460 between a tested sample and the CRS, there are 00:12:59.460 --> 00:13:02.480 two distinct possibilities. Okay. The intuitive 00:13:02.480 --> 00:13:05.039 assumption is that a mutation happens somewhere 00:13:05.039 --> 00:13:07.580 in your specific maternal lineage over the centuries, 00:13:07.860 --> 00:13:10.100 making you different from the standard. That 00:13:10.100 --> 00:13:12.500 makes sense. My ancestors evolved a new trait, 00:13:12.600 --> 00:13:15.120 so I diverge from the baseline. The second equally 00:13:15.120 --> 00:13:17.600 valid possibility is that the mutation actually 00:13:17.600 --> 00:13:21.759 arose in the lineage of the CRS itself. The CRS 00:13:21.759 --> 00:13:25.480 is just one woman's DNA and her ancestors experienced 00:13:25.480 --> 00:13:27.960 genetic mutations just like everyone else's. 00:13:28.120 --> 00:13:30.480 So a difference just means your two lineages 00:13:30.480 --> 00:13:32.600 don't match at that spot. It doesn't automatically 00:13:32.600 --> 00:13:35.279 mean your DNA is the changed version and hers 00:13:35.279 --> 00:13:37.779 is the original version. Exactly. That is a crucial 00:13:37.779 --> 00:13:40.299 paradigm shift. And the article provides some 00:13:40.299 --> 00:13:43.039 fantastic proof for this. The reference sequence 00:13:43.039 --> 00:13:46.169 itself contains its own unique Somewhat unusual 00:13:46.169 --> 00:13:48.330 quirks. It definitely does. The source notes 00:13:48.330 --> 00:13:50.789 the sequence has seven specific genetic variations 00:13:50.789 --> 00:13:53.250 or polymorphisms that are actually quite rare. 00:13:53.389 --> 00:13:56.210 Because her DNA is the baseline, those seven 00:13:56.210 --> 00:13:58.490 rare genetic quirks became the standard against 00:13:58.490 --> 00:14:00.389 which the rest of the world is measured. Can 00:14:00.389 --> 00:14:03.029 you walk us through those specific rare polymorphisms 00:14:03.029 --> 00:14:05.409 from this source? Certainly. The rare variations 00:14:05.409 --> 00:14:09.330 included in the CRS are at positions 263A, the 00:14:09.330 --> 00:14:13.889 sequence from 311C to 315C. Then there is 750A 00:14:13.889 --> 00:14:19.610 and 1438A, followed by 4769A, 8860AA, and finally 00:14:19.610 --> 00:14:23.779 15326A. That is a very specific list of rare 00:14:23.779 --> 00:14:26.220 quirks to have as the global standard. It really 00:14:26.220 --> 00:14:28.740 is. The inclusion of those rare polymorphisms 00:14:28.740 --> 00:14:31.259 in the baseline is a perfect reminder that the 00:14:31.259 --> 00:14:33.740 yardstick itself has its own unique bumpy shape. 00:14:34.000 --> 00:14:35.860 Which naturally leads to a massive question. 00:14:36.259 --> 00:14:38.919 If this European sequence from the 70s has rare 00:14:38.919 --> 00:14:41.960 mutations and once had cow DNA mixed into it 00:14:41.960 --> 00:14:44.139 and it's just one arbitrary branch on the tree, 00:14:44.320 --> 00:14:46.179 have scientists ever tried using a different 00:14:46.179 --> 00:14:48.080 baseline? They have. Have we ever said, let's 00:14:48.080 --> 00:14:49.679 try measuring from a different starting line? 00:14:50.009 --> 00:14:52.029 The scientific community has certainly explored 00:14:52.029 --> 00:14:55.070 alternatives. Researchers have utilized different 00:14:55.070 --> 00:14:57.990 reference sequences over the years to suit different 00:14:57.990 --> 00:15:01.409 studies. For instance, an African reference sequence 00:15:01.409 --> 00:15:04.509 representing one Yoluba individual has been used 00:15:04.509 --> 00:15:06.909 in place of the Cambridge sequence. And because 00:15:06.909 --> 00:15:09.570 it's a completely different person's DNA, the 00:15:09.570 --> 00:15:12.750 fundamental stats of the map change. The Yoruba 00:15:12.750 --> 00:15:15.110 sequence uses a different numbering system altogether, 00:15:15.350 --> 00:15:17.549 and it has a slightly different length. Right. 00:15:17.629 --> 00:15:21.769 While the actual length of the CRS is 16 ,568 00:15:21.769 --> 00:15:24.629 base pairs, the Yoruba reference sequence has 00:15:24.629 --> 00:15:29.269 a length of 16 ,571 base pairs. The Yoruba sequence 00:15:29.269 --> 00:15:32.070 isn't the only alternative either. The source 00:15:32.070 --> 00:15:34.049 mentions that researchers have also utilized 00:15:34.049 --> 00:15:36.289 sequences from African individuals in Uganda, 00:15:36.570 --> 00:15:39.230 as well as Swedish and Japanese sequences, depending 00:15:39.230 --> 00:15:41.230 on the specific populations they're studying. 00:15:41.639 --> 00:15:44.059 So scientists do have options. But here's where 00:15:44.059 --> 00:15:46.240 it gets really interesting. Because rather than 00:15:46.240 --> 00:15:49.340 just swapping one modern person's DNA for another 00:15:49.340 --> 00:15:52.659 modern person's DNA, there was a major push to 00:15:52.659 --> 00:15:56.419 change the paradigm entirely. In 2012. Yes, in 00:15:56.419 --> 00:16:00.059 2012, a group of researchers, led by Behar et 00:16:00.059 --> 00:16:02.779 al., proposed that we should replace the revised 00:16:02.779 --> 00:16:05.240 Cambridge reference sequence with something totally 00:16:05.240 --> 00:16:08.840 new. something called the RSRS. The RSRS stands 00:16:08.840 --> 00:16:11.559 for the Reconstructed Sapiens Reference Sequence. 00:16:11.559 --> 00:16:13.899 It is a profoundly different approach to genetic 00:16:13.899 --> 00:16:16.600 mapping. Reconstructed Sapiens Reference Sequence 00:16:16.600 --> 00:16:18.259 sounds like something out of a science fiction 00:16:18.259 --> 00:16:21.019 novel. What makes it so different? The proponents 00:16:21.019 --> 00:16:24.580 of the RSRS argue that using any random modern 00:16:24.580 --> 00:16:26.879 human as our baseline, whether they are European 00:16:26.879 --> 00:16:29.480 Yoruba or Japanese, is fundamentally flawed. 00:16:29.799 --> 00:16:32.000 Instead, they propose we should measure from 00:16:32.000 --> 00:16:34.679 the very root of the human family tree. The root? 00:16:34.840 --> 00:16:37.210 Yes. The RSRS represents the computationally 00:16:37.210 --> 00:16:39.809 reconstructed ancestral genome of mitochondrial 00:16:39.809 --> 00:16:42.669 Eve. Mitochondrial Eve, the theoretical maternal 00:16:42.669 --> 00:16:45.210 ancestor from which all currently known human 00:16:45.210 --> 00:16:49.070 mitochondria. Exactly. They mathematically reconstructed 00:16:49.070 --> 00:16:51.470 what they believe the mitochondrial DNA of that 00:16:51.470 --> 00:16:53.950 ancient common ancestor looked like. And cleverly, 00:16:53.950 --> 00:16:55.789 to avoid the literature confusion we talked about 00:16:55.789 --> 00:16:58.669 earlier with the 1999 revision, the RSRS proposal 00:16:58.669 --> 00:17:00.970 retains the exact same numbering system as the 00:17:00.970 --> 00:17:03.629 old CRS. So the filing system stays the same, 00:17:03.710 --> 00:17:06.450 but the underlying letters, the foundational 00:17:06.450 --> 00:17:08.710 baseline we are comparing ourselves against, 00:17:08.789 --> 00:17:12.730 would be this theoretical ancestral DNA, not 00:17:12.730 --> 00:17:16.339 the 1970s Cambridge DNA. Like changing the prime 00:17:16.339 --> 00:17:18.759 meridian of a map from Greenwich to the actual 00:17:18.759 --> 00:17:21.180 equator, but keeping the grid lines the same. 00:17:21.380 --> 00:17:24.599 That is a brilliant analogy. The core argument 00:17:24.599 --> 00:17:27.460 from researchers like Behar is that using the 00:17:27.460 --> 00:17:29.759 ancestral root makes it much more logical for 00:17:29.759 --> 00:17:32.160 comparing genetic changes across all different 00:17:32.160 --> 00:17:34.559 modern haplogroups. You're measuring how far 00:17:34.559 --> 00:17:37.359 everyone has independently evolved from a shared 00:17:37.359 --> 00:17:39.900 starting point. Rather than arbitrarily measuring 00:17:39.900 --> 00:17:42.299 how far everyone is from one random European 00:17:42.299 --> 00:17:44.890 branch on the tree. That makes an incredible 00:17:44.890 --> 00:17:47.789 amount of logical sense. But as with any major 00:17:47.789 --> 00:17:50.289 paradigm shift in science, you don't just erase 00:17:50.289 --> 00:17:52.529 a 30 -year -old baseline overnight without serious 00:17:52.529 --> 00:17:55.130 pushback. No, you certainly don't. We have to 00:17:55.130 --> 00:17:56.869 look at both sides of this fairly, and there 00:17:56.869 --> 00:17:58.710 is a fierce debate about this in the scientific 00:17:58.710 --> 00:18:01.430 community. It is a classic tension between theoretical 00:18:01.430 --> 00:18:04.650 elegance and practical utility. While proponents 00:18:04.650 --> 00:18:07.269 argue for the logical superiority of the RSRS, 00:18:07.650 --> 00:18:09.990 other prominent researchers like Bandelt and 00:18:09.990 --> 00:18:12.910 his colleagues in a 2014 paper cited in the article 00:18:12.910 --> 00:18:15.089 have strongly pushed back against the change. 00:18:15.430 --> 00:18:17.849 What is their primary argument for keeping the 00:18:17.849 --> 00:18:20.630 old, somewhat flawed Cambridge sequence? Their 00:18:20.630 --> 00:18:23.450 argument is rooted in historical continuity and 00:18:23.450 --> 00:18:26.390 the realities of scientific labor. Bandelt and 00:18:26.390 --> 00:18:28.730 others argue that the revised Cambridge reference 00:18:28.809 --> 00:18:31.470 sequence works perfectly fine as a standardized 00:18:31.470 --> 00:18:34.410 notation tool it is a known quantity Exactly. 00:18:34.589 --> 00:18:37.369 They argue that introducing a completely new 00:18:37.369 --> 00:18:39.950 baseline, even one that is theoretically more 00:18:39.950 --> 00:18:43.650 pure, introduces unnecessary complexity and potential 00:18:43.650 --> 00:18:46.589 for error into a system that is already universally 00:18:46.589 --> 00:18:48.930 understood. It's the ultimate if it ain't entirely 00:18:48.930 --> 00:18:51.150 broke, don't fix it argument. So we have this 00:18:51.150 --> 00:18:53.789 tension between those who want an ancestral baseline 00:18:53.789 --> 00:18:56.670 to reflect human evolution accurately and those 00:18:56.670 --> 00:18:58.589 who prefer the established historical baseline 00:18:58.589 --> 00:19:00.630 because it keeps the global filing system stable. 00:19:01.109 --> 00:19:03.470 And because of this ongoing philosophical and 00:19:03.470 --> 00:19:06.569 practical debate, the consumer DNA testing world 00:19:06.569 --> 00:19:09.490 has had to find a middle ground. The source specifically 00:19:09.490 --> 00:19:11.809 notes how companies are handling this schism. 00:19:12.170 --> 00:19:14.470 For example, the testing company Family Tree 00:19:14.470 --> 00:19:17.789 DNA currently reports maternal DNA results using 00:19:17.789 --> 00:19:20.150 both systems. Right. When you get your results, 00:19:20.309 --> 00:19:22.769 they show you your variations compared to the 00:19:22.769 --> 00:19:25.329 historical RCRS, and they also show you your 00:19:25.329 --> 00:19:28.480 variations compared to the ancestral RSRS. It 00:19:28.480 --> 00:19:30.640 is a highly practical way to bridge the gap, 00:19:30.819 --> 00:19:33.039 giving consumers and researchers the data they 00:19:33.039 --> 00:19:35.720 need, while the broader scientific community 00:19:35.720 --> 00:19:38.319 continues to debate the best standardized approach 00:19:38.319 --> 00:19:41.930 for the future. It really is. Okay, as we wrap 00:19:41.930 --> 00:19:43.849 up this deep dive, let's take a quick look back 00:19:43.849 --> 00:19:45.910 at the incredible journey we've unpacked today. 00:19:46.089 --> 00:19:47.910 It has been quite a journey. We started in the 00:19:47.910 --> 00:19:51.430 1970s marveling at the sheer manual effort of 00:19:51.430 --> 00:19:54.329 Fred Sanger's team sequencing a single woman's 00:19:54.329 --> 00:19:56.769 mitochondrial DNA. We learned about the 11 errors. 00:19:56.970 --> 00:19:59.269 And the bizarre reality of HeLa cells and cow 00:19:59.269 --> 00:20:02.509 DNA hiding in humanity's baseline genetic map 00:20:02.509 --> 00:20:06.690 for years. We explored the 1999 RCRS revision 00:20:06.690 --> 00:20:09.130 that cleaned up the mess but kept the old numbers 00:20:09.130 --> 00:20:12.009 to save the literature. And finally, we waded 00:20:12.009 --> 00:20:14.470 into the modern heated debate over whether to 00:20:14.470 --> 00:20:18.049 replace that historical artifact with the reconstructed 00:20:18.049 --> 00:20:21.049 root of mitochondrial Eve. This raises an important 00:20:21.049 --> 00:20:23.210 question, one that goes far beyond genetics. 00:20:23.650 --> 00:20:26.069 Science is often presented as a static collection 00:20:26.069 --> 00:20:29.329 of absolute facts, but it is actually a constant, 00:20:29.430 --> 00:20:32.289 sometimes messy process of refining our tools. 00:20:32.589 --> 00:20:34.450 We build a yardstick with the best technology 00:20:34.450 --> 00:20:37.049 we have, we use it, we eventually discover its 00:20:37.049 --> 00:20:40.240 flaws, and we iterate. The history of the Cambridge 00:20:40.240 --> 00:20:43.180 reference sequence is a perfect embodiment of 00:20:43.180 --> 00:20:45.779 that relentless, continuous refinement. It perfectly 00:20:45.779 --> 00:20:47.640 captures the human element of the scientific 00:20:47.640 --> 00:20:49.880 method. And I want to leave you, the listener, 00:20:50.000 --> 00:20:52.220 with a final thought to mull over as you go about 00:20:52.220 --> 00:20:54.400 your day. Okay. We just learned that our entire 00:20:54.400 --> 00:20:57.079 foundational baseline for understanding human 00:20:57.079 --> 00:20:59.900 genetic history was initially shaped by a single 00:20:59.900 --> 00:21:03.319 individual's DNA. was impacted by lab contamination 00:21:03.319 --> 00:21:06.240 and is held together by a numbering system that 00:21:06.240 --> 00:21:09.099 was intentionally left flawed just to keep old 00:21:09.099 --> 00:21:11.380 filing cabinets organized. So it makes you wonder 00:21:11.380 --> 00:21:14.220 how many other scientific baselines in our world, 00:21:14.339 --> 00:21:17.119 the standard measures and vital metrics we take 00:21:17.119 --> 00:21:19.519 for granted every single day, are actually just 00:21:19.519 --> 00:21:22.250 historical accidents waiting to be revised. Thank 00:21:22.250 --> 00:21:24.430 you so much for exploring this fascinating slice 00:21:24.430 --> 00:21:27.170 of scientific methodology with us. Yes. Thank 00:21:27.170 --> 00:21:29.430 you for joining us on this deep dive. We'll be 00:21:29.430 --> 00:21:31.609 back next time to unpack another stack of sources. 00:21:31.930 --> 00:21:34.450 Until then, keep questioning the baselines. Goodbye.