# Human Extinction **URL:** \ **Category:** Factual Questions\ **Created:** [August 4, 2017, 8:07am UTC](https://boards.straightdope.com/t/human-extinction/792755 "2017-08-04T08:07:04Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 5, 2017, 2:30pm UTC](https://boards.straightdope.com/t/human-extinction/792755/21 "2017-08-05T14:30:39Z")
> [@abashed](#): > > I’ve read that Homo-Sapiens may have been down to as low as 40 breeding pairs. What a close call! Where did you read that? ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 5, 2017, 3:24pm UTC](https://boards.straightdope.com/t/human-extinction/792755/22 "2017-08-05T15:24:39Z")
I’m not understanding something here … we’re saying that modern humans “have” Neanderthal genes and let’s assume 2% here … however, from [SciAm](https://www.scientificamerican.com/article/tiny-genetic-differences-between-humans-and-other-primates-pervade-the-genome/) we see that chimps and modern humans are only genetically 1% different … > [@](#): > > chimps and bonobos in particular take pride of place as our nearest living relatives, sharing approximately 99 percent of our DNA, with gorillas trailing at 98 percent. So, does that mean we’re more closely related to chimps than Neanderthals? … that makes no sense a’tall … ---
**Author:** ![Ann\_Hedonia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ann_hedonia/32/319_2.png) [@Ann\_Hedonia](https://boards.straightdope.com/u/Ann_Hedonia)\ **Post date:** [August 5, 2017, 3:39pm UTC](https://boards.straightdope.com/t/human-extinction/792755/23 "2017-08-05T15:39:47Z")
> [@Darren\_Garrison](#): > > Actually, it is more like 2 to 4 percent (in certain populations–Europeans more Neanderthal, Asians more Denisovian, Africans tiny amounts of either but with some sticky ghost spit.) So about the same degree of relation as a great-great-great grandparent. I just checked my 23 and Me report. They used to give it as a percentage and I think mine used to be 3.6. But they aren’t listing it that way anymore, they just say less than 4%. I’m in the 94th percentile of their database with 316 Neanderthal variants. They test 1436 markers. I had 2 variants on 30 markers and 1 variant on 256 markers. From a practical POV, all that they tell me is that I’m unlikely to have a hairy back or to sneeze after eating chocolate. :rolleyes: Basically, this fits with my discovery via 23 and Me that I’m REALLY white. And Northern European. All rumors of a more exotic ancestry - and there were rumors- were debunked by my 23 and Me testing. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 5, 2017, 3:48pm UTC](https://boards.straightdope.com/t/human-extinction/792755/24 "2017-08-05T15:48:44Z")
Humans and Neanderthals are just about equally similar to chimps, but each group has a few different differences. Let’s say that a chimp word has the spelling abcdef. But in most populations of modern humans, the word has changed to abcdgh. Except in many Europeans, the spelling has changed to abijef. Then scientist manage to sequence the Neanderthal genome and find that they also spell that word abijef. This fact is strong evidence that Europeans picked up that spelling from Neanderthal ancestors. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 5, 2017, 3:58pm UTC](https://boards.straightdope.com/t/human-extinction/792755/25 "2017-08-05T15:58:13Z")
Taking another bite of the apple, in both humans and Neanderthals, 99 percent of our genome is spelled the same as in chimps, but in each group, the typos are different. When distinctive typos are found both in Neanderthals and in a subset of humans but not in most other humans, it is an indication those genes likely were inherited from Neanderthal ancestors. But there are other genes that are spelled identically in humans, Neanderthals, _and_ chimps. When the spellings are identical, it is not only impossible to determine if that gene came from a human or a Neanderthal ancestor, but also a question without meaning. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 5, 2017, 4:40pm UTC](https://boards.straightdope.com/t/human-extinction/792755/26 "2017-08-05T16:40:15Z")
> [@watchwolf49](#): > > I’m not understanding something here … we’re saying that modern humans “have” Neanderthal genes and let’s assume 2% here … however, from [SciAm](https://www.scientificamerican.com/article/tiny-genetic-differences-between-humans-and-other-primates-pervade-the-genome/) we see that chimps and modern humans are only genetically 1% different … > So, does that mean we’re more closely related to chimps than Neanderthals? … that makes no sense a’tall … It’s… complicated. Here’s a thread I started many moons ago [on that subject.](http://boards.straightdope.com/sdmb/showthread.php?t=182445) ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 5, 2017, 4:42pm UTC](https://boards.straightdope.com/t/human-extinction/792755/27 "2017-08-05T16:42:55Z")
> [@John\_Mace](#): > > Where did you read that? > **[How Human Beings Almost Vanished From Earth In 70,000 B.C.](https://www.npr.org/sections/krulwich/2012/10/22/163397584/how-human-beings-almost-vanished-from-earth-in-70-000-b-c)** > > By some counts of human history, the number of humans on Earth may have skidded so sharply that we were down to just 1,000 reproductive adults. And a supervolcano might have been to blame. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 5, 2017, 4:47pm UTC](https://boards.straightdope.com/t/human-extinction/792755/28 "2017-08-05T16:47:45Z")
> [@John\_Mace](#): > > It’s… complicated. Here’s a thread I started many moons ago [on that subject.](http://boards.straightdope.com/sdmb/showthread.php?t=182445) Thanks … that might be the best information available … ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [August 5, 2017, 5:09pm UTC](https://boards.straightdope.com/t/human-extinction/792755/29 "2017-08-05T17:09:42Z")
> [@Sailboat](#): > > The first part has been answered (Toba). Wiki suggests that this is uncertain: > [@Wiki](#): > > The controversial Toba catastrophe theory, presented in the late 1990s to early 2000s, suggested that a bottleneck of the human population occurred c. 70,000 years ago, proposing that the human population was reduced to perhaps 10,000–30,000 individuals[8] when the Toba supervolcano in Indonesia erupted and triggered a major environmental change. Parallel bottlenecks were proposed to exist among chimpanzees, gorillas, rhesus macaques, orangutans and tigers.[9] The hypothesis was based on geological evidence of sudden climate change and on coalescence evidence of some genes (including mitochondrial DNA, Y-chromosome DNA and some nuclear genes)[10] and the relatively low level of genetic variation in humans.[8] > > However, subsequent research, especially in the 2010s, appeared to refute both the climate argument and the genetic argument. Recent research shows the extent of climate change was much smaller than believed by proponents of the theory.[11] In addition, coalescence times for Y-chromosomal and mitochondrial DNA have been revised to well above 100,000 years since 2011. Finally, such coalescence would not, in itself, indicate a population bottleneck, because mitochondrial DNA and Y-chromosome DNA are only a small part of the entire genome, and are atypical in that they are inherited exclusively through the mother or through the father, respectively. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [August 5, 2017, 5:18pm UTC](https://boards.straightdope.com/t/human-extinction/792755/30 "2017-08-05T17:18:11Z")
> [@watchwolf49](#): > > I’m not understanding something here … we’re saying that modern humans “have” Neanderthal genes and let’s assume 2% here … however, from [SciAm](https://www.scientificamerican.com/article/tiny-genetic-differences-between-humans-and-other-primates-pervade-the-genome/) we see that chimps and modern humans are only genetically 1% different … > So, does that mean we’re more closely related to chimps than Neanderthals? … that makes no sense a’tall … The statements refer to different things. One way to measure DNA divergence between species is to align the genomes and look at differences that have arisen through _base substitution_. This is a kind of mutation where just a single base changes. It is particularly important for phylogenetics, because it tends to occur at a regular rate through evolutionary time, providing a _molecular clock_ that can show which species are more or less closely related. If the clock can be calibrated through other lines of evidence, this measure of divergence allows us to infer speciation times. (Bear in mind that the base substitution rate does not reflect _other_ kinds of differences. There are also many insertions and deletions, from one base to large segments of DNA; there are duplications of segments of DNA; and in the human lineage the fusion of two entire chromosomes. These differences may obviously be important, but they are more difficult to quantify in a precise way.) If we look at genome divergence with this base substitution approach, we find that human and chimp DNA sequences have diverged by the oft-quoted figure of about 1%. In other words, since the human-chimp common ancestor around 4MYA, the number of single-base substitution mutations that have accumulated is around 1%. Using the same method, [human and Neanderthal genomes differ by just 0.3%](https://en.wikipedia.org/wiki/Neanderthal_genome_project#Findings) - as you would expect, with a more recent common ancestor. Now for the claim that [around 2% of the human genome comes from Neanderthals](https://en.wikipedia.org/wiki/Neanderthal_genome_project#History). This is talking about something completely different. The speculation is that long after we split into essentially distinct populations, recent interbreeding between humans and Neanderthals occurred, and that the now-extinct Neanderthal population contributed a small amount (perhaps 1%-4%) to the human genome, a process called [admixture](https://en.wikipedia.org/wiki/Genetic_admixture). How do researchers claim to know this? The human and Neanderthal populations diverged from a common ancestor into separate populations around half a million years ago, and in that time their genomes diverged by the 0.3% base substitution figure described above. These base substitutions are exactly the same things as the SNP (single nucleotide polymorphisms) markers that are used in DNA tests to identify your genomic ancestry as originating from populations in various parts of the word. In just the same way, a segment of DNA that carries the specific 0.3% of SNP markers that are found in Neanderthals marks the entire segment of DNA as being of Neanderthal _origin_, even though it is 99.7% identical. So, the evidence for recent admixture of Neanderthal DNA is that 1%-4% of the genome of non-African humans has the characteristic Neanderthal SNPs. But, again - that 1%-4% figure refers to the entire segment length that came from Neanderthals. 99.7% of the sequence in those segments is identical among all humans (African and non-African) and Neanderthals. It’s exactly the same thing as doing a DNA test and finding out (to your surprise) that 20% of your DNA comes from (say) Asian ancestry. That 20% refers to the total segment lengths that are identified as of Asian origin by the rare SNP differences, and it doesn’t contradict the fact that all humans share \>99% sequence identity. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 5, 2017, 5:44pm UTC](https://boards.straightdope.com/t/human-extinction/792755/31 "2017-08-05T17:44:31Z")
Thanks for that concise explanation. Just a minor correction in that the human/chip split is thought to have happened 5-7M years ago. By the time you get to 4M years ago, our ancestors were already walking upright. That is not to say that there might have even been some interbreeding between the populations then, but at 4M years ago our ancestors would be noticeably unchimp-like below the neck. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 5, 2017, 8:17pm UTC](https://boards.straightdope.com/t/human-extinction/792755/32 "2017-08-05T20:17:59Z")
> [@Xema](#): > > Wiki suggests that this is uncertain: Which is why I said that it was Toba\* or not \*Toba… ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [August 5, 2017, 8:38pm UTC](https://boards.straightdope.com/t/human-extinction/792755/33 "2017-08-05T20:38:17Z")
> [@abashed](#): > > [How Human Beings Almost Vanished From Earth In 70,000 B.C. : Krulwich Wonders... : NPR](http://www.npr.org/sections/krulwich/2012/10/22/163397584/how-human-beings-almost-vanished-from-earth-in-70-000-b-c) That’s not very convincing. Since the actual cite for the claim is not referenced, I’m going to guess that someone threw out a number that was the minimum there could have been for us to have survived at all, rather than the minimum that the data actually suggests. The whole idea of a human bottleneck is controversial, and if there was one, the general consensus puts it somewhere between 2,000 and 10,000 individuals. Maybe even more. ---
**Author:** ![Reddy\_Mercury](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@Reddy\_Mercury](https://boards.straightdope.com/u/Reddy_Mercury)\ **Post date:** [August 7, 2017, 4:38am UTC](https://boards.straightdope.com/t/human-extinction/792755/34 "2017-08-07T04:38:52Z")
Question is then are Homo Sapiens Sapiens, in our modern form actually a hybrid species? Not truly a “pure” Homo Sapiens Sapiens given the influx (albeit thousands of years ago) of Neanderthal and Denovisan DNA? Like if say the different Human species were separate, distinct branches of an evolutionary tree, did the intermingling of the different species cause the end of the pure Homo Sapiens branch? ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:17am UTC](https://boards.straightdope.com/t/human-extinction/792755/35 "2017-08-07T09:17:41Z")
> [@John\_Mace](#): > > That’s not very convincing. Since the actual cite for the claim is not referenced, I’m going to guess that someone threw out a number that was the minimum there could have been for us to have survived at all, rather than the minimum that the data actually suggests. > > The whole idea of a human bottleneck is controversial, and if there was one, the general consensus puts it somewhere between 2,000 and 10,000 individuals. Maybe even more. I guess it’s very difficult to be that accurate and they’re covering themselves, although it would be interesting to look at the study in question. ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:19am UTC](https://boards.straightdope.com/t/human-extinction/792755/36 "2017-08-07T09:19:33Z")
> [@Reddy\_Mercury](#): > > Question is then are Homo Sapiens Sapiens, in our modern form actually a hybrid species? Not truly a “pure” Homo Sapiens Sapiens given the influx (albeit thousands of years ago) of Neanderthal and Denovisan DNA? > > Like if say the different Human species were separate, distinct branches of an evolutionary tree, did the intermingling of the different species cause the end of the pure Homo Sapiens branch? I’m not sure anyone can really answer that question.:dubious: ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [August 7, 2017, 10:27am UTC](https://boards.straightdope.com/t/human-extinction/792755/37 "2017-08-07T10:27:04Z")
> [@Reddy\_Mercury](#): > > Question is then are Homo Sapiens Sapiens, in our modern form actually a hybrid species? Not truly a “pure” Homo Sapiens Sapiens given the influx (albeit thousands of years ago) of Neanderthal and Denovisan DNA? > > Like if say the different Human species were separate, distinct branches of an evolutionary tree, did the intermingling of the different species cause the end of the pure Homo Sapiens branch? The idea of a “species” is actually a blurry concept. If define different species as two groups that _cannot_ interbreed and produce viable, fertile offspring then Humans, Neanderthals, Denisovians, spit ghosts, etc. obviously aren’t different species. If you define different species as two groups that most of the time don’t interbreed, but on the occasion that they do, sometimes the offspring may be viable and fertile, then Humans, Neanderthals, Denisovians, and spit ghosts were never separate species to begin with. So calling each group different species or calling them different subspecies or races of the same species is a definitional problem. ---
**Author:** ![Banksiaman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/banksiaman/32/3334_2.png) [@Banksiaman](https://boards.straightdope.com/u/Banksiaman)\ **Post date:** [August 7, 2017, 11:15am UTC](https://boards.straightdope.com/t/human-extinction/792755/38 "2017-08-07T11:15:53Z")
Isn’t this exciting!? This is us trying to understand of our human ancestry and often what we were certain of last week has been dramatically changed by some new finding yesterday. And discoveries of that magnitude are happening every month or two. It makes it hard to keep up with, but Wow!!! The discussion on the shared genetic legacy we have with Neanderthals etal reminds to recommend _The Inheritors_, by William Golding. A fictional account of the way the encounter may have happened. Better than _Lord of the Flies_ - 4 chefs hats at least. While we were distinct human lineages, in reality our overall appearance and limited array of material culture was probably not very different. Just like crocodiles and alligators, the genetic distance is invisible to the naked eye, while the overall similarities would be all too evident. [Previous page](https://boards.straightdope.com/t/human-extinction/792755.md?page=1)