Mosaicism: The genome varies from cell to cell
nytimes.com
nytimes.com
The answer is that ants are not organisms, they are organs. The ant colony is the organism. It just happens to be made of parts that are not physically connected to each other.
Well, it turns out that humans are much like ants in this regard. A single human individual cannot reproduce. Even a single fertile couple cannot successfully reproduce in the wild (if you doubt this, watch a few episodes of Naked and Afraid). The minimum viable reproductive unit for homo sapiens is a tribe or a village.
This sort of organizational grouping is found at all of the levels of abstraction in life. Even your DNA is not really a unified whole, it's a bunch of genes that have glommed together in a cooperative effort to reproduce themselves, but it's not an organized or homogeneous effort. That's why you have freeloaders ("junk DNA") and defectors (cancer genes) who put their own interests above those of the group. What happens at the cellular and molecular level is really not so different from what happens in human societies. The presence of brains changes the dynamic, but not in any fundamental way. At the end of the day, it's all just self-replicating information looking for an ecological niche and a reproductive edge. The idea that human individuals are somehow special in this process is mostly a prejudice brought on by our particular point of view, namely, the fact that our thoughts reside in brains that are strongly bound to bodies. The ability to see beyond onesself can be both powerful and humbling.
Do you have evidence for this that's not a reality TV show?
Edit: I have found the Lykov family who had two children in isolation; they did already have two children who would have been 13 and 6 at the time of the third child's birth in isolation. https://en.wikipedia.org/wiki/Lykov_family
You were able to find one wiki article on a curious case of a family who, unlike billions of other people, survived as individuals for less than 50 years in partial isolation. That's impressive, but it doesn't change the basic facts of human survival.
Case in point, in the first paragraph of the link you provided about the Lykovs, the article says only one daughter yet survives (as of 1988, so they are probably all gone now).
Minimum viable populations are partially about day to day survival and team work, but in the long term it's about genetic diversity which is critical for long-term population survival. Evidence: all of biology?
That suggests it's far more viable than you might think. It's just more attractive places to live currently have people living there. Opportunity's for solitude where far greater when global population was lower, but it's unlikely for such things to enter written history.
But left no descendants.
Yes. Let's start with the fact that there are no recorded instances of an isolated human couple successfully reproducing in the wild ever. Merely having a baby doesn't count. To be a viable evolutionary strategy you have to raise that baby to maturity and then that baby has to reproduce themselves.
In fact, this is not unique to humans. It's true of all simians. In fact, it's true for the vast majority of mammals. The only exceptions I can think of are some species of cats: leopards, cheetahs, tigers, mountain lions.
We can also reason from first principles: you need a minimum viable population in order to maintain genetic diversity. So even if it were possible for isolated human couples to reproduce, you'd need more than one instance of this, and these families would somehow have to find each other in order to procure mates. How are they going to do that?
I remember going into back country with some friends as a teen, miles into 'the middle of nowhere'. Second day camping I see someone run by in yoga pants pushing a stroller as it turns out we where about 300 feet from a ski trail and people would run down the mountain in the summer for fun.
If couple has kids and those kids find someone in a local tribe then both tribes and lone families would have worked. In effect you are trying to redefine his argument not just in terms of recorded history but also both couples not an individual one.
You're attacking a straw man. Of course a couple can reproduce if they are in proximity to a tribe. But that still requires a tribe. It is a couple in isolation that is not viable.
QED they can reproduce in isolation.
The point is: for your scenario to play out, a tribe has to exist (and it has to be close enough for the couple's offspring to find it, but that's a detail). No tribe, no viable reproduction. Hence, the tribe is the minimum viable unit, even if it also occasionally supports an isolated couple somewhere in the vicinity.
Yes, humans are somewhat like ants in that they are usually social. Humans are adaptable enough to survive in pairs, though lack of specialization means they won't necessarily live the most comfortable life, so it would be an unusual choice. But there's nothing elective about ants' socialism. So in the end I don't think your argument works.
No. Those species have specialized adaptations that allow them to live in isolation, which humans lack. And it's not just humans. All simians lack these adaptations. Indeed, the vast majority (perhaps all -- I can't think of a single counterexample) of non-carnivore mammals lack them.
https://www.researchgate.net/publication/224771432_Lynch_M_C...
People obviously are viable reproductive organisms in a technical/literal sense. But... the way people (and our nearest cousins) actually reproduce is in couples within a tribe/village/troop. People are evolved to reproduce this way and people evolved by reproducing this way.
Separately but also related, there's a growing sentiment that biological networks are self-similar - higher-level network-modeled abstractions are in fact topologically similar to lower-level subnetworks. This analogy may seem almost Hofstadter-esque at this point, but in a few years, who knows...
Some links:
[1] https://www.nature.com/articles/srep07628
[2] http://rsif.royalsocietypublishing.org/content/9/74/2131
You are not wrong, but the way you answer it it is just concept definition.
Can you recommend any good books about genetics and natural selection to people who don't have a biology background? I can handle some math, but I just break software for a living and I don't know biology.
Sorry for the sidetrack, but thanks for posting this. I've always wondered about some of the higher order implications of natural selection, and ants are a great example. Like how megacolonies take in ants from other places, that's so crazy because it doesn't make sense once you're looking at a small enough perspective but makes perfect sense at a larger scale. Bees are cool too.
Thanks!
(Well, depends a bit on the definitions, I'd still say that ants are organisms, but so is the ant colony, and yes, you always have to see the bigger picture)
I don't get what the NYT is trying to achieve with their "reporting" here.
(BTW, the title here on HN has been changed, for anyone coming a bit later to these comment threads)
Not only is it not universal knowledge, there are substantial cohorts of people who will vehemently deny that it is true. In fact, there are people asking for additional evidence in other branches of this very discussion!
I mean, nothing that would be relevant to the question at hand, in my opinion.
Because the topic still is as linked above, and subsumed in this simple proposition: The genome varies from cell to cell.
Great. What a discovery! More news at 11!
Or is someone seriously arguing that genetic mutation is not universal knowledge?
(Excluding "flat-earth" level stuff, but I would assume that as given on HN. Maybe I am wrong again)
Well, no. But there are a lot of people who vehemently deny that humans are in any way analogous to ants.
> This sort of organizational grouping is found at all of the levels of abstraction in life. Even your DNA is not really a unified whole, it's a bunch of genes that have glommed together in a cooperative effort to reproduce themselves, but it's not an organized or homogeneous effort. That's why you have freeloaders (which are called "junk DNA") and defectors (cancer) who put their own interests above those of the group. What happens at the cellular and molecular level is really not so different from what happens in human societies. The presence of brains changes the dynamic, but not in any fundamental way. At the end of the day, it's all just self-replicating information looking for an ecological niche and a reproductive edge. The idea that human individuals are somehow special in this process is mostly a prejudice brought on by our particular point of view, namely, the fact that our thoughts reside in brains that are strongly bound to bodies. The ability to see beyond onesself can be both powerful and humbling.
Ant Colony Is Likened to Human Body : a 1985 Research study https://www.washingtonpost.com/archive/politics/1985/07/05/a...
Secrets of a Superorganism https://askabiologist.asu.edu/explore/secrets-superorganism
I am not quite sure to what extent you mean this. I would add that the bottle neck on evolutionary futures for our genes imposed by our reproductive system is very strong, and that there is no obvious analogy in societies. The existence of such a strong bottleneck of course shifts the game theoretical dynamics of cooperation and defection, strongly enabling cooperation between somatic cells (as you say, with cancer as an exception).
> Trichoplax adhaerens is the only extant representative of phylum Placozoa, which is a basal group of multicellular animals (metazoa). Trichoplax are very flat organisms around a millimetre in diameter, lacking any organs or internal structures. They have two cellular layers: the top epitheloid layer is made of ciliated "cover cells" flattened toward the outside of the organism, and the bottom layer is made up of cylinder cells that possess cilia used in locomotion, and gland cells that lack cilia. Between these layers is the fibre syncytium, a liquid-filled cavity strutted open by star-like fibres.
https://en.wikipedia.org/wiki/Trichoplax
I like these creatures because they are on the cusp of multicellularity: you can force them through a sieve that separates their cells which will then crawl around independently and try to reform the organism. You can dye two trichoplax different colors, force them through the sieve, and the cells will mix and form piebald organisms. So, they're like tribes of cells (IMHO.)
I am confused by this, because this seems to be the "group selection" idea that is vociferously rebutted by Dawkins and others.
It is really not clear to me what the bright line is between group selection and kin selection. If social groups are genetically similar (which is most often the case in nature and human society), group selection and kin selection appear to be equivalent.
I did. Well the first several chapters at least. I did not find a convincing answer to the question I am raising here.
> The phenotype of a gene is not necessarily constrained by any physical boundaries.
Sure it's not necessarily constrained. But in practice there is very high correlation between family relatedness and physical proximity / social group.
If the main rebuttal against group selection is "families can be spread out", I don't think that warrants the level of criticism that is leveled at it. An organism surrounded by genetically unrelated peers is the exception, not the rule.
EDIT: Reading a bit more, I think I may be understanding this distinction better. "Kin selection" and "group selection" are more different than the names suggest. "Kin selection" means that natural selection incentivizes an individual to be altrustic towards their own kin. "Group selection" means that natural selection will favor the survival of an entire group over another group based on the comparative genetic strengths of the two groups.
> Even your DNA is not really a unified whole, it's a bunch of genes that have glommed together in a cooperative effort to reproduce themselves, but it's not an organized or homogeneous effort. That's why you have freeloaders ("junk DNA") and defectors (cancer genes) who put their own interests above those of the group.
"Cancer genes" don't exist in the sense that there aren't genes that specifically cause cancer. If there were then every individual with a full gene complement would get cancer. What you're referring to are certain alleles that can arise which change cellular processes so as to break cooperative patterning of cell behavior. If you're lecturing in evolution it might be nice to use a technically correct description to match the Dawkinsian semantic splicing you're resting on :) Call them "oncogenic alleles" instead.
"Junk DNA" is a blind concept that conflates sequence complexity with function. The argument goes that these pieces of DNA are just copies of each other and serve no obvious purpose, thus they are junk that "freeloads" off their host. This ignores the fact that these elements exist in virtually all complex organisms, and have lineages that last tens or hundreds of millions of years, which is longer than the lifespan of most species. If they were only an energetic drag on their host they would be selected out over these time scales. Instead, they appear to serve important purposes in genomes. There is a huge amount of evidence that this "junk" is also an "organ" of the genome that provides essential function in an evolutionary sense. This perspective is old, more than 30 years, and the first reference to it I'm aware of is from a study in 1983 that showed that Escherichia coli with transposons evolved faster than those without: https://www.nature.com/articles/303633a0
That some members of a population are sterile doesn't require you to completely rearrange your definition of biology, speceis, and organism.
It is not "some" ants that are sterile. The vast majority of them (like >99%) are sterile. That does demand an explanation.
Firstly, the drones creating offspring would lead firstly into a population explosion followed by a population collapse after viable and attainable nutrition sources nearby have been depleted. Once the population collapses to low enough numbers, even cannibalism does not work anymore and eventually that genetic line dies out.
Also, it is presumable there would be fighting over resources, and maybe multiple genetic makeups within a single nest also opens up the door for attacks from other nests, since detecting who is a friend and who is not could be difficult, making the nest (and its genetic makeup) vulnerable.
Also, the minimum reproductive unit for a mobile homo sapiens is obviously a man and a woman. But is it viable, too? I say yes. Their offspring can wander out away from their parents and find another isolated offspring that is fsr enough genetically, and create progeny and repeat the process. If the humans are somehow not mobile, then a larger group ("tribe") is needed to avoid inbreeding with its detrimental effects.
But all the evidence says no.
A cartoon of the HIV life cycle: https://blogs.scientificamerican.com/observations/watch-the-...
The complexity insides eukaryotic cells is startling, and compared to individual molecules they are massive. (Prokaryotic cells are 0.1 - 5 microns, while eukaryotic ones are 10-100 microns. That means eukaryotic cells are larger in volume by 2-9 orders of magnitude! It also lowers the impressiveness of comparisons between the number of gut bacteria cells and human cells.) If you think of each cell as a person, then the body is an army of 30 trillion soldiers each with his own copy of instructions to follow (which he copied from someone else) and many possible ways to get hurt or die. It's not so surprising that some fractions of the soldiers will have very small errors in their copy of the instructions, which they will pass on as copies to other soldiers, or that individuals could get a tape worm and still fight.
Let's say we take the hardware basis -- cpu, instruction sets, registers, buses, etc. -- as the 'organic chemistry' analogue -- the substrate. Just the basic cell, which is a profoundly amazing machine, would require layer upon layer of software. By the time we reach the level of an 'organ' or 'system' along the biological model, it would be a monster.
We humans, for example, have apparently (per my search engine) somewhere between 10^13 to 10^14 cells. That's 4 to 5 orders of magnitude larger than the total number of computers on this planet.
You might like my crufty and slowwwly-loading page http://www.clarifyscience.info/part/Atoms for "nanoview" (zoom so that 1 nm looks like 1 mm). And http://bionumbers.hms.harvard.edu/ to look up biological numbers. So cells are zoomed to large garbage bags, rooms and buildings, proteins[1] look like bits of Play-Doh, and atoms like sand.[2]
[1] http://www.clarifyscience.info/stable/2015/mol-mach-2014-pos... [2] http://www.clarifyscience.info/assets/2017-Atoms/assets0/wk/...
[0] One discussion about this: https://news.ycombinator.com/item?id=16079735
From the argument from design:
> One looks at a simple computer, and sees evidence of intelligent design.
> One looks at a Sun Sparc 20 and... um... well... Okay, One looks at a DEC Alpha and sees evidence of intelligent design.
And from the counter argument:
> If you think the network implies intelligent design, you haven't seen our network.
> Optogenetics is a biological technique which involves the use of light to control cells in living tissue, typically neurons, that have been genetically modified to express light-sensitive ion channels. It is a neuromodulation method that uses a combination of techniques from optics and genetics to control and monitor the activities of individual neurons in living tissue—even within freely-moving animals—and to precisely measure these manipulation effects in real-time.
Bio is crazy complex. We've been poking the brain for a century now, and we have basically gotten no-where. At least we know that now. Take astrocytes/glia as a tiny example. These are the 'glue' cells in a brain that hold and feed the neurons. Sure, they do that, but a lot of new research is saying that they help modulate the synapse as well, the fundamental thing that makes thinking happen. Maybe. We basically have no idea now. We can't even say how many astrocytes there are in a typical brain. Is it 50%, is it 10%? Each new study overturns the last. It's chaos. What even is a synapse? We have no idea. Multiply this over every tissue in a body. And then that's only humans, let alone turtles and birds and bacteria and viruses etc.
One must always remember that bio was 'designed' by a very drunk, very horny, illiterate schizophrenic over 4.5 billion years with an average design cycle of about 22 minutes (~10E14 total cycles). It makes no sense because it never did.
The article discusses genetic post-meiotic changes that propagate differentially through the body. We knew it happened for a while now too, but it was always presented as a curiosity or an anomaly. We are now learning that it is much more common than we anticipated. Like presented in the article, it might actually explain some clinical phenotypes as well.
https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male...
"Secondly, the fraternal birth order effect operates through a biological mechanism during prenatal life, not during childhood or adolescence. Direct evidence for this is the fact that the fraternal birth order effect has been found even in males not raised with their biological brothers – it has been determined that biological brothers increase the odds of homosexuality in later-born males even if they were reared in different households, whereas non-biological siblings, such as step-brothers or adopted brothers, have no effect on male sexual orientation."
That is consistency with a "kin-selection" theory of homosexuality, that within a family, evolutionary factors favor having partially non-reproductive members in a family (perhaps because in a family with two males, on average, the total reproductive fitness is greater where there is one father and one uncle, not two fathers)
Furthermore, what math is so "clear", that you completely gloss over it?
> A gay person would have to result in their siblings having 2x as many children
Should have been:
> A gay person would have to result in their siblings having 2x as many additional children
Here's the math:
An individual's children have 50% of their genes. Their nieces and nephews share 25% of their genes. Therefore, if the hypothesis is that homosexuality evolved to promote the production of nieces and nephews at the expense of producing direct offspring, this adaptation would need to result in at least two nieces/nephews for each offspring that the homosexual individual would have produced directly.
So, if we assume a stable population where each couple produces 2 offspring, a gay person would be giving up producing 2 of their own children. In order for this strategy to break even, it would have to result in their siblings producing 4 offspring, in addition to the offspring that they would have had anyway.
Possible, but not likely.
On top of the math just being heavily stacked against this being an explanation, there are other reasons why it is unlikely:
1. If this were a successful strategy, you would expect to see a much higher prevalence of gay people than we currently do (<5% of the population).
2. There are already adults who take on this hypothetical role of assistant to the breeders: grandmothers. And they avoid the fertility tradeoff because they are evolved to stop being fertile at a certain point in their lives.
Nitpicking: We have the XY system but birds have the ZW system where the male birds have the chromosomes ZZ and the female birds have the chromosomes ZW (More info: https://en.wikipedia.org/wiki/Sex-determination_system )
I still can't find out if in this case the male birds have a random inactive Z and are mosaic. I guess that there is something similar, but I'm not sure.
1: http://www.askabiologist.org.uk/answers/viewtopic.php?id=929...
I mean, I would think that it's not so much external factors influencing your genes directly, per se. But certain genes being called into play and others not.
Or is - likely? - a combo of both? That is internal genetic variance, as well as the ability to be influences by external factors. It would seem, the latter would be the ideal, the most flexible / advantageous.
I am only asking questions to point out the answer probably isn't as simple as the poster seem to believe.
https://twitter.com/degenrolf/status/998856273725743104?s=21
Is that what HN has come to? Really?
I'm really sorry my friend.
They (downvoters) fail to realize that they are shooting the messengers, nothing more. But smart people understand. They know and will never cease to keeping them honest..
Genetics and the human body have proven to be increasingly complex.
this seems a bit reductive.
sometimes people asking leading questions that are a bit... let's say tired, aren't all that interesting. if there is a point to be made, they should just make it.
"smart people" (as you say) sometimes prefer forthright discussion.
[0] https://www.theguardian.com/commentisfree/2013/jan/07/violen...
[1] http://theconversation.com/child-lead-exposure-linked-to-agg...
[2] https://en.wikipedia.org/wiki/Lead_poisoning
...
I'm just trying to warn about the pitfalls of monocausal explanations for complex issues..
You should try to ask the OP the same question..
But, to be fair, the title of the submission to HN has been changed, to something a lot less of clickbait.
Maybe I would not have engaged otherwise, actually. Makes you think..
But still, downvotes = disagreement, I thought HN would be better than that.
Apparently, I was wrong.
I don't know, maybe you should have a talk with some post-structuralists, or with some other folks who seem to believe that xyz is a "social construct"..
downvotes can also be for perceiving questions as posed in bad faith, non-sequiturs, being reductive, rude comments, etc.
But I was not asking in bad faith, it is beyond me why anyone would even want to do that.
Okay, this is the Internet, I know, and you cannot tell from across the screen. That old drama.
But still, I don't agree that an uncharitable interpretation should be the standard on HN that everyone just downright assumes..
Nope, downvotes can be for many reasons, disagreement is not required to downvote. (I often downvote comments that I agree with and find non-useful in context, and upvote comments I disagree with but which contribute to productive discussion.)
I agree in theory, but I would like to hear some justification why other comments, even if unrelated, get downvoted as well then.
i'm not quite sure how "abolishing prisons" is suggested by what they posted. what leads you to that?
I just extrapolated a bit too unconstrained maybe. Okay, you can accuse me of erecting a straw man now.
But the thing is, I don't know how many times I've seen this (or very similar) debates unfold. Definitely getting a bit tired of it, to be honest. So I just though, why not skip ahead a bit, leave out some of the usual steps, you know?
But please enlighten me.. Maybe I am getting it wrong, or am just not seeing it..
But sure, just put it all on "biochemical processes".. and no one is responsible for anything any more. Brave New World.
For example, if you have an underdeveloped prefrontal cortex then you are going to be more impulsive and have a hard time delaying gratification. These people are way more susceptible to committing crimes and it is purely down to bad luck that they weren't born with the right genes (or had some sort of injury that damaged their PFC). Another example is if you have a smaller amygdala, you're going to have a higher pain tolerance and experience less fear than someone with a normal sized amygdala. Again, this can change your behavior quite a bit as you won't be able to relate to what the average person experiences when they are in pain. These people will have less moral compass than others.
With those things in mind, Sapolsky agrees that if an individual poses a threat to others, we should still lock them in prison for the good of society. But the more we understand what leads to human behavior, the more we're going to realize how many things are out of our control (almost all of it).
When did this notion take hold that we can answer such complex matters with simple solutions?
Do people on here even realize how old this stupid Nature vs Nurture debate is?
Probably not. I guess most older HN users have already abandoned ship, leaving only the greenhorns behind.
At least that would explain it.
And again, I am not arguing for anything here. I am just the Devil's Advocate.
I don't see why the nature vs nurture debate is stupid or why how old it is matters? Clearly both things determine human behavior. The main point to be made in Sapolskys book is that almost all determinants of your behavior are out of your control. You don't choose which country you're born in, what genes you have, whether your brain develops properly, whether your parents are kind people or terrible people, what neighborhood you grow up in, what race or gender you are. Perhaps you should read Sapolskys book.
> use the original title, unless it is misleading or linkbait.
The original title was arguably both. :-)
What's the "it" referring to in the title?
The body? But the body itself has no DNA to properly speak of.
A single cell? That is not what the article is saying.
Trying to use the same construct for a different sentence:
"Every person in this room should have worn a suit. Except he didn't" -> a single person in the room didn't wear a suit, and I am probably looking at him while saying this.
"Every person in this room should have worn a suit. Except they didn't" -> there are several people in the room who didn't wear a suit, this feels closer to the meaning of the piece's title?
I think it passed because it was in the title, rather than the body of the article.
It's the same thing.
The "it" does indeed refer to "a cell"; the second sentence is like saying, "except (some particular cell) doesn't (have the same DNA as all the others."
If this (kinda silly) format is to be kept, a better headline is, "All the Cells in Your BOdy Have the same DNA. Except They Don't."
An even better headline is one that is sans the clickbaity style - just "Cells in the Human Body Don't All Have the Same DNA."