5 ms·

The headline is a little surprising since DNA only survives intact for relatively short time but the fragment analysis made it possibleto go back 5000 years was

The headline is a little surprising since DNA only survives intact for relatively short time but the fragment analysis made it possibleto go back 5000 years was kind of wild to non expert here. Also my immediate reaction was how could this be good genetic thing to pass on but all the matches were children either under one year or died prior to birth.

maxerickson 3y ago
It can just be that the genetic mixing that occurs during meiosis is a good trade off with any issues that it introduces.
LordKeren 3y ago
Infertility rates are extremely high for individuals with Down’s syndrome, so it’s very uncommon to pass on Downs Syndrome from an adult with Down’s to a child
- im3w1l 3y ago
  Given that Down Syndrome is caused by an extra chromosome, I'm kinda curious how that would be inherited. Like if you have two people with Down's would there be a possibility of offspring with an extra chromosome pair? Could that in the long term lead to speciation? Would it be possible that only one of the three chromosomes is passed on from each parent, leading to a normal and healthy child?
  - thereticent 3y ago
    It's an interesting topic. The primary cause of Down syndrome is trisomy of chromosome 21, which is what you described. That form is not inherited. A much less common cause, mosaicism, is a random occurrence during cell division and isn't inherited either. The only form that can be inherited (that we know of) is caused by translocation. Basically a piece of one chromosome can become switched with a piece of another chromosome. If no information is lost, that's a balanced translocation. Those usually still produce a normal phenotype. When the balanced translocation is passed down a generation, it can lose information or pick up extra information and become unbalanced. If the extra information is from chromosome 21, that can become Down syndrome. That's a simplistic explanation, but should do the job.
    - im3w1l 3y ago
      Right that makes sense. I guess what happens in all of these scenarios is having an extra copy of one particular gene, causes it to become overexpressed, which in turn leads to all these issues?
      - thereticent 3y ago
        It's actually many, many genes that are overexpressed and result in the Down syndrome phenotype. My work is with adults with DS and Alzheimer disease--in this case, triplication of the amyloid precursor protein (APP) gene on chromosome 21 nearly guarantees accelerated development of cerebral amyloid deposition compared to typically developing people. But that's just a miniscule part of the Down syndrome phenotype.
    - thereticent 3y ago
      It's actually many, many genes that are overexpressed and result in the Down syndrome phenotype. My work is with adults with DS and Alzheimer disease--in this case, triplication of the amyloid precursor protein (APP) gene on chromosome 21 nearly guarantees accelerated development of cerebral amyloid deposition compared to typically developing people. But that's just a miniscule part of the Down syndrome phenotype.
  - RoyalHenOil 3y ago
    >Like if you have two people with Down's would there be a possibility of offspring with an extra chromosome pair? Could that in the long term lead to speciation? A similar phenomenon is common in plants. While humans have two copies of DNA, one from each parent, many plants contribute more than one copy of DNA to their offspring, resulting in plants with many more than just two copies of DNA. The number of copies a plant has can vary within the same species. Notably, domesticated plants often have more copies of their DNA than their wild counterparts have, yet they are still reproductively compatible. In animals like us, multiple copies of DNA, or even just of individual chromosomes, are much more risky, which is why it's so rare (those embryos are typically nonviable). However, different animal species do often have different numbers of chromosomes, which does provide a pathway to evolutionary divergence and speciation. Typically, species with different numbers cannot reproduce (e.g., humans and chimps), and when they can, the result is often sterile (e.g., horses and donkeys). There are several ways that species can gain or lose new chromosomes as they evolve, and you are right: duplication of an existing chromosome is one of them, although pretty rare because it often leads to serious health problems or sterility. (More common is the splitting of a chromosome or the fusing of two chromosomes, since these preserve all the genes without duplication. Another possibility is the total deletion of a chromosome, but this is extremely rare because it typically kills the embryo.) So yes, theoretically, fertile men with trisomy 21 Down's syndrome (they are usually sterile, but there have been exceptions) and women with trisomy 21 Down's syndrome could get together and start a new hominid branch. Over time, the twin chromosomes would undergo selection and diverge from one another, likely in a way that would improve on the general health and fertility issues that people with this syndrome commonly struggle with. The chances of this happening are very low, but it is certainly not unprecedented in the history of evolution.
    - Tabular-Iceberg 3y ago
      They certainly have a good ecological niche to get started in. When I see people with Down syndrome out and about I only get more inclined to support policies that allocate resources to them. Of course this niche doesn’t exist everywhere, for example in Iceland they have a very aggressive abortion campaign against the syndrome.
  - Tabular-Iceberg 3y ago
    Turns out that this already happens: https://rarediseases.info.nih.gov/diseases/12480/tetrasomy-21 https://rarediseases.info.nih.gov/diseases/12480/tetrasomy-2... The bad news is that the prognosis is even worse than for the trisomy.
dekhn 3y ago
Human DNA can be preserved for a very long time if it's in cold, dry conditions and little oxygen. And the DNA tends to be pretty damaged/fragmented anyway. Samples up to 300Kya have been sequenced from caves in Spain.
ajkjk 3y ago
Apparently there have been a ton of advances in reading ancient DNA that make a lot more than 5000 years possible. There is a fairly readable summary of it all in the form of a somewhat-dry book, "Who We Are and How We Got Here", by David Reich.
- adolph 3y ago
  The Reich book is phenomenal. For something a little more accessible, there is the Nova episode: "Hunt for the Oldest DNA." It's a bit breathless if one has already encountered Reich, but gets the gist across. https://www.youtube.com/watch?v=c2ppreiB1PQ https://www.youtube.com/watch?v=c2ppreiB1PQ
User3456335 3y ago
Perhaps the existence of atypical "weaker" children promotes compassion in the culture ultimately leading to better outcomes for the culture as a whole.
- mistermann 3y ago
  Exactly what I was thinking, it's an interesting idea.
- Retric 3y ago
  All species that sexually reproduce occasionally have the wrong number of chromosomes show up in an offspring. In humans it occurs in ~0.6% of live births. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3681172/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3681172/ Down syndrome is an example of that anomaly rather than some mutation that’s passed down. It’s an extra partial or complete copy of chromosome 21, and therefore can happen to any couple.
  - stvltvs 3y ago
    In other words, Down syndrome isn't inherited therefore not something evolutionary forces can act on. The only way around that is if the base rate of chromosomal anomaly is heritable, yes?
    - lazide 3y ago
      Or general human reproductive ‘cost’ is heritable. Think r/K evolutionary strategies [https://en.m.wikipedia.org/wiki/R/K_selection_theory https://en.m.wikipedia.org/wiki/R/K_selection_theory] A species that can produce 1000+ offspring (or more) per mating (with multiple matings per adult lifespan) - like most insects, seaturtles/squids, etc. has little incentive to have high precision/accuracy reproduction. One that does a small handful (whales, elephants, etc), has a lot of incentive to do so (or self abort early on if there is an issue). This gets complicated though, because while a single individual in a species which is predominantly r strategy (few offspring), can be ‘more’ on the K side, and vice versa. And a species which has too much consistency, both genetically and ‘approach’ is very susceptible to inbreeding/mono-cropping issues where a single event/disease can wipe them out, or they can even destroy themselves due to recessive traits. So there is a general (but diffuse!) evolutionary pressure towards a degree of mutation/error in reproduction in even the most hardcore ‘r’ species (which will necessarily produce a lot of noise/‘wasted paths’) at the species level, alongside a hard evolutionary pressure to reduce it for individuals. In for example humans. Or elephants. Or whales. This is also why things like rich/poor, healthy/sick, pretty/ugly, strong/weak, etc. will never go away - they’re outcome distributions along a probability curve due to fundamental different approaches by individual humans due to the necessity of how humans have to be in order for humanity (the species) to survive. Individuals have strong incentives to ‘tip the scales’ in various ways of course, and societies (at a minimum!) have strong incentives to stop them. It’s why aborting based on gender is illegal in India, for instance. [https://pubmed.ncbi.nlm.nih.gov/7920120/ https://pubmed.ncbi.nlm.nih.gov/7920120/] Because if everyone had the same attributes in order for everyone to be ‘pretty’ or ‘strong’ or ‘rich’ or whatever, then some hypothetical weight-lifting-infectious-disease (or a famine, or an attack by jealous anti-weightlifters) would wipe out the whole population. And if everyone optimized for ‘rich’ genes (whatever that means), then society would implode, because that literally couldn’t work. And those types of situations, albeit less light hearted, have, do, and will continue to happen eventually.
tokai 3y ago
Geogenetics is a hot field. Boundaries are being pushed.
tzs 3y ago
Relatively recent advances allow for going back way more than 5000 years. Just last week Nova on PBS did an episode profiling one of the main contributors to pushing the limit back. https://www.pbs.org/video/hunt-for-the-oldest-dna-zckys0/ https://www.pbs.org/video/hunt-for-the-oldest-dna-zckys0/
- elif 3y ago
  It seems to me that this would validate the practice of sarcophagizing Egyptian pharaohs such that they can be reborn in the afterlife. As far as I understand it, we now have the technological capacity to do so, and simply lack the moral and legal capability. For me this would push occams razor toward the notion that endeavoring to build monumental generational-construction-project tombs was not an act of cultural vanity but actually an informed and practical decision made with some form of ancient knowledge.
  - jhardy54 3y ago
    Being able to read DNA != being able to clone humans.
    - lazide 3y ago
      Also, being able to clone humans != being able to restore a human (with all their memories, experiences, personality, etc.).
  - pavel_lishin 3y ago
    Even if we could clone them, is it really a form of rebirth? They'd have no memory of their previous life - it's as much a form of rebirth as me freezing my sperm to be used after my death.
NoPedantsThanks 3y ago
[dead]
deleted 3y ago
[deleted]
sinuhe69 3y ago
With teeth, you can go really far, because in cool, dry conditions they can be preserved for tens of thousands, if not hundreds of thousands, of years. Also, you only need a tiny amount of genetic material to analyse. Of course, having some genetic material is very different from having complete DNA. I guess in this case the researchers just got lucky and got the right segment after all.

maxerickson 3y ago

It can just be that the genetic mixing that occurs during meiosis is a good trade off with any issues that it introduces.

LordKeren 3y ago

Infertility rates are extremely high for individuals with Down’s syndrome, so it’s very uncommon to pass on Downs Syndrome from an adult with Down’s to a child

im3w1l 3y ago
Given that Down Syndrome is caused by an extra chromosome, I'm kinda curious how that would be inherited. Like if you have two people with Down's would there be a possibility of offspring with an extra chromosome pair? Could that in the long term lead to speciation? Would it be possible that only one of the three chromosomes is passed on from each parent, leading to a normal and healthy child?
- thereticent 3y ago
  It's an interesting topic. The primary cause of Down syndrome is trisomy of chromosome 21, which is what you described. That form is not inherited. A much less common cause, mosaicism, is a random occurrence during cell division and isn't inherited either. The only form that can be inherited (that we know of) is caused by translocation. Basically a piece of one chromosome can become switched with a piece of another chromosome. If no information is lost, that's a balanced translocation. Those usually still produce a normal phenotype. When the balanced translocation is passed down a generation, it can lose information or pick up extra information and become unbalanced. If the extra information is from chromosome 21, that can become Down syndrome. That's a simplistic explanation, but should do the job.
  - im3w1l 3y ago
    Right that makes sense. I guess what happens in all of these scenarios is having an extra copy of one particular gene, causes it to become overexpressed, which in turn leads to all these issues?
    - thereticent 3y ago
      It's actually many, many genes that are overexpressed and result in the Down syndrome phenotype. My work is with adults with DS and Alzheimer disease--in this case, triplication of the amyloid precursor protein (APP) gene on chromosome 21 nearly guarantees accelerated development of cerebral amyloid deposition compared to typically developing people. But that's just a miniscule part of the Down syndrome phenotype.
  - thereticent 3y ago
    It's actually many, many genes that are overexpressed and result in the Down syndrome phenotype. My work is with adults with DS and Alzheimer disease--in this case, triplication of the amyloid precursor protein (APP) gene on chromosome 21 nearly guarantees accelerated development of cerebral amyloid deposition compared to typically developing people. But that's just a miniscule part of the Down syndrome phenotype.
- RoyalHenOil 3y ago
  >Like if you have two people with Down's would there be a possibility of offspring with an extra chromosome pair? Could that in the long term lead to speciation? A similar phenomenon is common in plants. While humans have two copies of DNA, one from each parent, many plants contribute more than one copy of DNA to their offspring, resulting in plants with many more than just two copies of DNA. The number of copies a plant has can vary within the same species. Notably, domesticated plants often have more copies of their DNA than their wild counterparts have, yet they are still reproductively compatible. In animals like us, multiple copies of DNA, or even just of individual chromosomes, are much more risky, which is why it's so rare (those embryos are typically nonviable). However, different animal species do often have different numbers of chromosomes, which does provide a pathway to evolutionary divergence and speciation. Typically, species with different numbers cannot reproduce (e.g., humans and chimps), and when they can, the result is often sterile (e.g., horses and donkeys). There are several ways that species can gain or lose new chromosomes as they evolve, and you are right: duplication of an existing chromosome is one of them, although pretty rare because it often leads to serious health problems or sterility. (More common is the splitting of a chromosome or the fusing of two chromosomes, since these preserve all the genes without duplication. Another possibility is the total deletion of a chromosome, but this is extremely rare because it typically kills the embryo.) So yes, theoretically, fertile men with trisomy 21 Down's syndrome (they are usually sterile, but there have been exceptions) and women with trisomy 21 Down's syndrome could get together and start a new hominid branch. Over time, the twin chromosomes would undergo selection and diverge from one another, likely in a way that would improve on the general health and fertility issues that people with this syndrome commonly struggle with. The chances of this happening are very low, but it is certainly not unprecedented in the history of evolution.
  - Tabular-Iceberg 3y ago
    They certainly have a good ecological niche to get started in. When I see people with Down syndrome out and about I only get more inclined to support policies that allocate resources to them. Of course this niche doesn’t exist everywhere, for example in Iceland they have a very aggressive abortion campaign against the syndrome.
- Tabular-Iceberg 3y ago
  Turns out that this already happens: https://rarediseases.info.nih.gov/diseases/12480/tetrasomy-21 https://rarediseases.info.nih.gov/diseases/12480/tetrasomy-2... The bad news is that the prognosis is even worse than for the trisomy.

dekhn 3y ago

Human DNA can be preserved for a very long time if it's in cold, dry conditions and little oxygen. And the DNA tends to be pretty damaged/fragmented anyway. Samples up to 300Kya have been sequenced from caves in Spain.

ajkjk 3y ago

Apparently there have been a ton of advances in reading ancient DNA that make a lot more than 5000 years possible. There is a fairly readable summary of it all in the form of a somewhat-dry book, "Who We Are and How We Got Here", by David Reich.

adolph 3y ago
The Reich book is phenomenal. For something a little more accessible, there is the Nova episode: "Hunt for the Oldest DNA." It's a bit breathless if one has already encountered Reich, but gets the gist across. https://www.youtube.com/watch?v=c2ppreiB1PQ https://www.youtube.com/watch?v=c2ppreiB1PQ

User3456335 3y ago

Perhaps the existence of atypical "weaker" children promotes compassion in the culture ultimately leading to better outcomes for the culture as a whole.

mistermann 3y ago
Exactly what I was thinking, it's an interesting idea.
Retric 3y ago
All species that sexually reproduce occasionally have the wrong number of chromosomes show up in an offspring. In humans it occurs in ~0.6% of live births. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3681172/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3681172/ Down syndrome is an example of that anomaly rather than some mutation that’s passed down. It’s an extra partial or complete copy of chromosome 21, and therefore can happen to any couple.
- stvltvs 3y ago
  In other words, Down syndrome isn't inherited therefore not something evolutionary forces can act on. The only way around that is if the base rate of chromosomal anomaly is heritable, yes?
  - lazide 3y ago
    Or general human reproductive ‘cost’ is heritable. Think r/K evolutionary strategies [https://en.m.wikipedia.org/wiki/R/K_selection_theory https://en.m.wikipedia.org/wiki/R/K_selection_theory] A species that can produce 1000+ offspring (or more) per mating (with multiple matings per adult lifespan) - like most insects, seaturtles/squids, etc. has little incentive to have high precision/accuracy reproduction. One that does a small handful (whales, elephants, etc), has a lot of incentive to do so (or self abort early on if there is an issue). This gets complicated though, because while a single individual in a species which is predominantly r strategy (few offspring), can be ‘more’ on the K side, and vice versa. And a species which has too much consistency, both genetically and ‘approach’ is very susceptible to inbreeding/mono-cropping issues where a single event/disease can wipe them out, or they can even destroy themselves due to recessive traits. So there is a general (but diffuse!) evolutionary pressure towards a degree of mutation/error in reproduction in even the most hardcore ‘r’ species (which will necessarily produce a lot of noise/‘wasted paths’) at the species level, alongside a hard evolutionary pressure to reduce it for individuals. In for example humans. Or elephants. Or whales. This is also why things like rich/poor, healthy/sick, pretty/ugly, strong/weak, etc. will never go away - they’re outcome distributions along a probability curve due to fundamental different approaches by individual humans due to the necessity of how humans have to be in order for humanity (the species) to survive. Individuals have strong incentives to ‘tip the scales’ in various ways of course, and societies (at a minimum!) have strong incentives to stop them. It’s why aborting based on gender is illegal in India, for instance. [https://pubmed.ncbi.nlm.nih.gov/7920120/ https://pubmed.ncbi.nlm.nih.gov/7920120/] Because if everyone had the same attributes in order for everyone to be ‘pretty’ or ‘strong’ or ‘rich’ or whatever, then some hypothetical weight-lifting-infectious-disease (or a famine, or an attack by jealous anti-weightlifters) would wipe out the whole population. And if everyone optimized for ‘rich’ genes (whatever that means), then society would implode, because that literally couldn’t work. And those types of situations, albeit less light hearted, have, do, and will continue to happen eventually.

tokai 3y ago

Geogenetics is a hot field. Boundaries are being pushed.

tzs 3y ago

Relatively recent advances allow for going back way more than 5000 years. Just last week Nova on PBS did an episode profiling one of the main contributors to pushing the limit back. https://www.pbs.org/video/hunt-for-the-oldest-dna-zckys0/ https://www.pbs.org/video/hunt-for-the-oldest-dna-zckys0/

elif 3y ago
It seems to me that this would validate the practice of sarcophagizing Egyptian pharaohs such that they can be reborn in the afterlife. As far as I understand it, we now have the technological capacity to do so, and simply lack the moral and legal capability. For me this would push occams razor toward the notion that endeavoring to build monumental generational-construction-project tombs was not an act of cultural vanity but actually an informed and practical decision made with some form of ancient knowledge.
- jhardy54 3y ago
  Being able to read DNA != being able to clone humans.
  - lazide 3y ago
    Also, being able to clone humans != being able to restore a human (with all their memories, experiences, personality, etc.).
- pavel_lishin 3y ago
  Even if we could clone them, is it really a form of rebirth? They'd have no memory of their previous life - it's as much a form of rebirth as me freezing my sperm to be used after my death.

NoPedantsThanks 3y ago

[dead]

deleted 3y ago

[deleted]

sinuhe69 3y ago

With teeth, you can go really far, because in cool, dry conditions they can be preserved for tens of thousands, if not hundreds of thousands, of years. Also, you only need a tiny amount of genetic material to analyse. Of course, having some genetic material is very different from having complete DNA. I guess in this case the researchers just got lucky and got the right segment after all.