Why sex evolved; no one knows (Introduction)
by David Turell 
, Friday, June 17, 2016, 14:44 (3080 days ago)
Simply splitting apart as bacteria do is complex enough, but much simpler than eukaryotic sex, which has lead to cells that are highly complex compared to bacteria: - https://aeon.co/ideas/sex-is-a-costly-molecular-kind-of-wizardry-why-evolve-it - "Sex is unknown in bacteria - the simplest and most ancient living cells on Earth - that reproduce by simply splitting into two. Evolving considerably later, eukaryotes are built of much larger and awfully complex cells, their insides full of organelles and membranous labyrinths buzzing with sophisticated molecular machinery and cargo-transport networks. Unlike bacteria, very few eukaryotic species revert to strict asexuality, and those that do seem to be relatively short-lived on the evolutionary timescale. Sex is costly, but it also appears to be essential for the long-term survival of complex life. - "Some of the most talented theorists have striven to understand why. Myriad explanations made their way into science journals and textbooks - from the earliest proposals that sex generates variation and speeds up adaptation, to mathematical models demonstrating that gene shuffling bolsters resistance to parasites and slows down the accumulation of hazardous genetic defects. But even with the overwhelming amount of attention the problem has received over the years, it is still considered unsolved. - *** - "But the past few decades have seen a paradigm shift in the understanding of how complex life came into being. All Archezoa turned out to be secondarily simplified versions of cells as complex as any other unicellular eukaryote that lives today. Genetic composition analyses showed that genes required for sexual reproduction permeate all eukaryotic groups, from animals and plants, to unicellular amoeba and even Giardia. The last common ancestor of all eukaryotes and the first truly complex cell was already sexual - which is why the ultimate solution to the evolutionary enigma of sex should be sought within the origin of eukaryotes themselves. - *** - "Around 2 billion years ago in a world ruled by microbes, a bacterial species formed a close symbiotic partnership with another simple cell - an archaeon. The interaction was so tight that bacterial symbionts eventually colonised the insides of archaea and were gradually transformed into mitochondria - the organelles of our cells specialising in energy production. The chimeric cell grew and expanded, using the genetic material of both partners and the newly available mitochondrial energy source to forge a cell of unparalleled complexity, inventing countless eukaryotic features along the way - including sex. - *** - "Lane is convinced that the pre-eukaryotic cell was rescued by its ability to fuse with similar cells - a skill that bacteria do not possess. Frequent cell unions brought several copies of the genome together, each from a different individual and each containing a different set of mutations or newly acquired symbiont genes. Cell fusions masked lethal defects and ensured that the host always possessed a full set of indispensable chromosomes and vital genes. Fusions facilitated gene mixing through recurrent recombination, stabilised the genome, and promoted its further expansion. - "Quite unexpectedly, the evolutionary puzzle of sex comes down to the origin of cell fusion, not just recombination, in the early stages of the transition to complex life. .... Critically, both hypotheses predict that the ability to fuse was a direct consequence of the bacterial invasion into the archaeal host, putting the origin of the first sexual trait well before the development of the eukaryotic cell was complete. - "Regardless of what the initial benefit of sexual cell fusion was, the repercussions were immense. Sex rescued the emerging eukaryotic cell when it was most vulnerable; without sex, the evolutionary transition would have plainly failed. While sex appears to be critical for the long-term survival of contemporary eukaryotes, it was not itself an invention of the eukaryotic cell. It is far more likely that the eukaryotic cell evolved only because sex - through cell fusion and recombination - was invented in ancestral chimeric lineages leading to the last common ancestor of all complex life." - Comment: Still lots of theory with n o solid answers. Margulies theory of fusion of bacteria to create mitochondria is obviously a key component. Eukaryotic cells are huge complex factories compared to bacteria. It is clear that combining genetic pools helped to create this complexity. Like the origin of life mystery, this event (sex) is just as mysterious. Why not consider God creating both giant steps?
Why sex evolved; no one knows
David's comment: Still lots of theory with no solid answers. Margulies theory of fusion of bacteria to create mitochondria is obviously a key component. Eukaryotic cells are huge complex factories compared to bacteria. It is clear that combining genetic pools helped to create this complexity. Like the origin of life mystery, this event (sex) is just as mysterious. Why not consider God creating both giant steps? - If your God exists, I don't have a problem with the idea of him dabbling to revolutionize the course of life. But I do have a problem with the idea of him preprogramming the first cells to pass on every other innovation and every natural wonder throughout the history of life, let alone the suggestion that the whole caboodle was created just for the sake of homo sapiens.
Why sex evolved; no one knows
by David Turell , Saturday, June 18, 2016, 14:16 (3079 days ago) @ dhw
> dhw: If your God exists, I don't have a problem with the idea of him dabbling to revolutionize the course of life. But I do have a problem with the idea of him preprogramming the first cells to pass on every other innovation and every natural wonder throughout the history of life, let alone the suggestion that the whole caboodle was created just for the sake of homo sapiens.-The key to our differences revolves about just one question: how 'special' do you consider the appearance of H. sapiens? I follow Adler in thinking we are different in kind, based primarily on the development of an advanced consciousness. That we were better survivors than the other Homo types is obvious. That a scattergun hominin group appeared at this last existing stage of evolution needs to be considered in recognizing humans as a final target of progression of evolution. We came from apes and they are unchanged in the interim. We have developed the power to destroy the Earth, which we struggle to control. We are the endpoint of evolution although it is possible, given enough time we might change in form slightly. But finally what is there to improve, if we consider evolution as an improving process?
Why sex evolved; no one knows
dhw: If your God exists, I don't have a problem with the idea of him dabbling to revolutionize the course of life. But I do have a problem with the idea of him preprogramming the first cells to pass on every other innovation and every natural wonder throughout the history of life, let alone the suggestion that the whole caboodle was created just for the sake of homo sapiens.-DAVID: The key to our differences revolves about just one question: how 'special' do you consider the appearance of H. sapiens? I follow Adler in thinking we are different in kind, based primarily on the development of an advanced consciousness. That we were better survivors than the other Homo types is obvious. That a scattergun hominin group appeared at this last existing stage of evolution needs to be considered in recognizing humans as a final target of progression of evolution. We came from apes and they are unchanged in the interim. We have developed the power to destroy the Earth, which we struggle to control. We are the endpoint of evolution although it is possible, given enough time we might change in form slightly. But finally what is there to improve, if we consider evolution as an improving process?-I can't see into the future, but no one in his right mind would deny the enormous gulf between our powers and those of other species. However, even if we are as good as it gets (I don't mean morally - plenty of room for improvement there!), that does not mean every organism and natural wonder, extinct and extant, was created just for our sake. You have separated the two parts of my sentence, but they go together. The key difference between us is your attempt to explain the whole higgledy-piggledy bush of evolution as being preprogrammed or dabbled in order to produce humans. (We discovered that “the balance of nature” just meant the continuation of life, and that does not require humans.) This is why we have spent so much time on the weaverbird's nest. Why would your God have specifically designed such wonders for our sake? And if his final target was homo sapiens, what do you mean by “we need to consider” a scattergun hominin group? Again I would ask why your God created “multiple choice” programmes for all the different hominins if he just wanted homo sapiens. It makes far more sense to me that (theistic version) he enabled organisms to do their own designing, punctuated by the odd dabble. In other words, it is your anthropocentric, homo sapiens interpretation of the whole history of evolution that is the key difference between us. (See the “Talbott” thread for more.)
Why sex evolved; no one knows
by David Turell , Sunday, June 19, 2016, 15:25 (3078 days ago) @ dhw
dhw: You have separated the two parts of my sentence, but they go together. The key difference between us is your attempt to explain the whole higgledy-piggledy bush of evolution as being preprogrammed or dabbled in order to produce humans. (We discovered that “the balance of nature” just meant the continuation of life, and that does not require humans.)-Correct. The balance OF nature is only a mechanism to let the necessary energy supply continue to provide energy so life can continue to evolve.->dhw: This is why we have spent so much time on the weaverbird's nest. Why would your God have specifically designed such wonders for our sake? -God used evolution as a process to produce humans. The weaver bird fits into it own balance of nature in its ecologic niche. Tying the bird to us is a straw man argument. The bird is small part of an overall process.-> dhw: And if his final target was homo sapiens, what do you mean by “we need to consider” a scattergun hominin group? Again I would ask why your God created “multiple choice” programmes for all the different hominins if he just wanted homo sapiens.-Again the process He seems to prefer: what I have described as shotgun advances of complexity. Complexification is an overarching principle of the evolutionary process we observe.-> dhw: It makes far more sense to me that (theistic version) he enabled organisms to do their own designing, punctuated by the odd dabble. In other words, it is your anthropocentric, homo sapiens interpretation of the whole history of evolution that is the key difference between us. (See the “Talbott” thread for more.)-I look at the overall impression of 'process'. I am a 'lumper' trying to see design processes existing in evolutionary history. You seem to be a 'splitter' worrying about the weaver bird, which is an inconsequential side issue that only raises the dabble issue, nothing more.
Why sex evolved; no one knows
dhw: You have separated the two parts of my sentence, but they go together. The key difference between us is your attempt to explain the whole higgledy-piggledy bush of evolution as being preprogrammed or dabbled in order to produce humans. (We discovered that “the balance of nature” just meant the continuation of life, and that does not require humans.) DAVID: Correct. The balance OF nature is only a mechanism to let the necessary energy supply continue to provide energy so life can continue to evolve.-It therefore provides no explanation whatsoever for the course evolution has taken. -dhw: This is why we have spent so much time on the weaverbird's nest. Why would your God have specifically designed such wonders for our sake? DAVID: God used evolution as a process to produce humans. The weaver bird fits into it own balance of nature in its ecologic niche. Tying the bird to us is a straw man argument. The bird is small part of an overall process.-It is anything but a straw man, since you insist that your God specially designed it, even though his aim was to produce humans. Previously you clung to the “balance of nature” explanation, which we now agree is irrelevant. The colossal variety of life, with 99% of species going extinct, clearly has nothing whatsoever to do with the production of humans, and so if your God exists, there has to be another reason for his special design of the nest and the millions of other natural wonders. If you can't find one, perhaps you will consider the possibility that he did NOT specially design the nest, but gave the weaverbird and all its fellow miracle-workers the means of devising their own wonders. (See below for why.)-dhw: And if his final target was homo sapiens, what do you mean by “we need to consider” a scattergun hominin group? Again I would ask why your God created “multiple choice” programmes for all the different hominins if he just wanted homo sapiens. DAVID: Again the process He seems to prefer: what I have described as shotgun advances of complexity. Complexification is an overarching principle of the evolutionary process we observe.-This is the process that happened. If he exists, then of course it's the process he prefers, but it clearly runs counter to your hypothesis that he has preprogrammed it to produce homo sapiens. The higgledy-piggledy evolution of humans, just like that of all other species extinct and extinct, suggests that his reason for using this process was to produce higgledy-piggledy evolution! The best way to do that would have been to give organisms their own individual means of innovating (with the proviso that he could dabble). Why would he want the higgledy-piggledy? Ah, we must try to read God's mind - which you don't like doing, apart from insisting that you know his purpose - but since we are apparently in his image, maybe he thought it might be more interesting than having a whole load of clockwork toys that couldn't do anything without his “guidance”.-I agree with you completely, however, that complexification is an overarching principle when we consider the development from single cell to ourselves. That is why, in passing, I cannot make head or tail of the “front end loading” gene-loss article, which suggests the exact opposite. dhw: It makes far more sense to me that (theistic version) he enabled organisms to do their own designing, punctuated by the odd dabble. In other words, it is your anthropocentric, homo sapiens interpretation of the whole history of evolution that is the key difference between us. (See the “Talbott” thread for more.) DAVID: I look at the overall impression of 'process'. I am a 'lumper' trying to see design processes existing in evolutionary history. You seem to be a 'splitter' worrying about the weaver bird, which is an inconsequential side issue that only raises the dabble issue, nothing more.-I wish you did look at the overall impression of ‘process'. Your vision seems to me to focus on humans and to offer no explanation of the seemingly chaotic comings and goings of life's history, with its vast variety of species and natural wonders that have nothing to do with humans. If you really want to be a ‘lumper', you need to find a reason for the whole higgledy-piggledy, and that means finding a reason for the weaver bird's nest as well as for the human brain.
Why sex evolved; no one knows
by David Turell , Sunday, June 26, 2016, 15:48 (3071 days ago) @ dhw
DAVID: Correct. The balance OF nature is only a mechanism to let the necessary energy supply continue to provide energy so life can continue to evolve. > > dhw: It therefore provides no explanation whatsoever for the course evolution has taken.-Correct. It supplies energy for the process. -> DAVID: God used evolution as a process to produce humans. The weaver bird fits into it own balance of nature in its ecologic niche. Tying the bird to us is a straw man argument. The bird is small part of an overall process. > > It is anything but a straw man, since you insist that your God specially designed it, even though his aim was to produce humans. Previously you clung to the “balance of nature” explanation, which we now agree is irrelevant.-See above. not truly irrelevant, but not a driving force for evolution.--> dhw: The colossal variety of life, with 99% of species going extinct, clearly has nothing whatsoever to do with the production of humans, and so if your God exists, there has to be another reason for his special design of the nest and the millions of other natural wonders.-God provided a drive to complexity, which is what evolution shows.- > dhw: If you can't find one, perhaps you will consider the possibility that he did NOT specially design the nest, but gave the weaverbird and all its fellow miracle-workers the means of devising their own wonders. -I still doubt that. Somehow He helped them design the nest.-> dhw: And if his final target was homo sapiens, what do you mean by “we need to consider” a scattergun hominin group? Again I would ask why your God created “multiple choice” programmes for all the different hominins if he just wanted homo sapiens.-Because the example we see is that all of evolution is scattergun.- > DAVID: Again the process He seems to prefer: what I have described as shotgun advances of complexity. Complexification is an overarching principle of the evolutionary process we observe. > > This is the process that happened. If he exists, then of course it's the process he prefers, but it clearly runs counter to your hypothesis that he has preprogrammed it to produce homo sapiens.-Why don't you like His obvious method? Because you like your way of doing things which is logical. God's logic, from the evidence is to complexify and scattergun resultant creatures.-> > dhw: I agree with you completely, however, that complexification is an overarching principle when we consider the development from single cell to ourselves. That is why, in passing, I cannot make head or tail of the “front end loading” gene-loss article, which suggests the exact opposite.-Front-end loading with all possibilities on board allows for all sorts of results, just as we've seen in the h-p bush. > > dhw: I wish you did look at the overall impression of ‘process'. Your vision seems to me to focus on humans and to offer no explanation of the seemingly chaotic comings and goings of life's history, with its vast variety of species and natural wonders that have nothing to do with humans. If you really want to be a ‘lumper', you need to find a reason for the whole higgledy-piggledy, and that means finding a reason for the weaver bird's nest as well as for the human brain.-I don't need to find reasons. That is your problem. I look at process and the resultant end as the basis of my position. If I can't read God's planning process in His mind, I can't fill in reasons that satisfy a human mind.
Why sex evolved; no one knows
DAVID: God provided a drive to complexity, which is what evolution shows.-But he could have provided a drive to complexity in the form of individual intelligences working out their own means of survival and/or improvement (which clearly entailed increased complexity), as opposed to your excruciatingly complicated 3.8-billion-year programme and/or dabbling.-dhw: If you can't find one [a reason], perhaps you will consider the possibility that he did NOT specially design the nest, but gave the weaverbird and all its fellow miracle-workers the means of devising their own wonders. DAVID: I still doubt that. Somehow He helped them design the nest.-You can't think of a reason why he would want to design it, and you don't know how he “helped”, but you doubt that he could have provided the weaverbird with the intelligence to do it. Why? dhw: And if his final target was homo sapiens, what do you mean by “we need to consider” a scattergun hominin group? Again I would ask why your God created “multiple choice” programmes for all the different hominins if he just wanted homo sapiens. DAVID: Because the example we see is that all of evolution is scattergun.-All of evolution, including human evolution, is indeed “scattergun”, which makes nonsense of the idea that everything, including the weaverbird's nest, was planned for a specific purpose, other than for the “scattergun” history of life as we know it! Why plan or dabble the higgledy-piggledy if all he wanted was homo sapiens? Here is your non-answer: DAVID: Why don't you like His obvious method? Because you like your way of doing things which is logical. God's logic, from the evidence is to complexify and scattergun resultant creatures.-That fits in with my hypothesis and not yours! If your God preprogrammed or dabbled the weaverbird's nest or different forms of hominin, it was NOT scattergun. It's only scattergun if your God leaves organisms to do their own inventing. The idea of your God preprogramming the first cells to pass on a set of nest-building/hominizing lottery tickets to choose from only adds another layer of pointless complication. -Dhw: If you really want to be a ‘lumper', you need to find a reason for the whole higgledy-piggledy, and that means finding a reason for the weaver bird's nest as well as for the human brain. DAVID: I don't need to find reasons. That is your problem. I look at process and the resultant end as the basis of my position. If I can't read God's planning process in His mind, I can't fill in reasons that satisfy a human mind.-You quite rightly (in my view) spend a great deal of time asking how the complexities and wonders of life could possibly have come about by chance. How would you react if our atheist friends told you that was your problem? If they and you can't make sense of your own hypotheses, that may be because those hypotheses are wrong!
Why sex evolved; no one knows
by David Turell , Tuesday, June 28, 2016, 21:18 (3068 days ago) @ dhw
DAVID: God provided a drive to complexity, which is what evolution shows. > > dhw: But he could have provided a drive to complexity in the form of individual intelligences working out their own means of survival and/or improvement (which clearly entailed increased complexity), as opposed to your excruciatingly complicated 3.8-billion-year programme and/or dabbling.-Complexity requires mental planning. What did your version of God put into your supposed cell intelligence to provide the ability for speciation? I expect you cannot answer. > > dhw: If you can't find one [a reason], perhaps you will consider the possibility that he did NOT specially design the nest, but gave the weaverbird and all its fellow miracle-workers the means of devising their own wonders. > DAVID: I still doubt that. Somehow He helped them design the nest. > > dhw: You can't think of a reason why he would want to design it, and you don't know how he “helped”, but you doubt that he could have provided the weaverbird with the intelligence to do it. Why?-Easy. God is in control in my version of theistic evolution. > > > DAVID: Why don't you like His obvious method? Because you like your way of doing things which is logical. God's logic, from the evidence is to complexify and scattergun resultant creatures. > > dhw: That fits in with my hypothesis and not yours! If your God preprogrammed or dabbled the weaverbird's nest or different forms of hominin, it was NOT scattergun. It's only scattergun if your God leaves organisms to do their own inventing.-The h-p bush looks scattergun. Why not think God did it on His own? He would have to pre-program intelligent organisms which is quite a complicated approach compared to direct action by Him. Dabble always is a possibility. > dhw: You quite rightly (in my view) spend a great deal of time asking how the complexities and wonders of life could possibly have come about by chance. How would you react if our atheist friends told you that was your problem? If they and you can't make sense of your own hypotheses, that may be because those hypotheses are wrong!-All hypotheses are unproven guesses based on what is observed, nothing more, nothing written in stone. Again, what God does may not fit human logic. Until we discover how speciation works, and we may never if it is a result of God's direct action (Saltation), then our hypotheses are moot..
Why sex evolved; no one knows
DAVID: God provided a drive to complexity, which is what evolution shows. dhw: But he could have provided a drive to complexity in the form of individual intelligences working out their own means of survival and/or improvement (which clearly entailed increased complexity), as opposed to your excruciatingly complicated 3.8-billion-year programme and/or dabbling.-DAVID: Complexity requires mental planning. What did your version of God put into your supposed cell intelligence to provide the ability for speciation? I expect you cannot answer.-Speciation occurs through innovation, and in my version the cells have the intelligence to restructure themselves into new forms. Your God didn't have to “put” anything into that intelligence. Intelligence is enough! dhw: You can't think of a reason why he [God] would want to design it [the nest], and you don't know how he “helped”, but you doubt that he could have provided the weaverbird with the intelligence to do it. Why? DAVID: Easy. God is in control in my version of theistic evolution.-So if you believe it, it must be true, even though it doesn't make sense even to you. With my hypothesis, there is no need to even try and explain why or how God designed it. He didn't. He enabled the weaverbird to do it. Simple! DAVID: Why don't you like His obvious method? Because you like your way of doing things which is logical. God's logic, from the evidence is to complexify and scattergun resultant creatures. dhw: That fits in with my hypothesis and not yours! If your God preprogrammed or dabbled the weaverbird's nest or different forms of hominin, it was NOT scattergun. It's only scattergun if your God leaves organisms to do their own inventing.-DAVID: The h-p bush looks scattergun. Like you, I think it is scattergun. But that argues against every new organism and natural wonder being purposely preprogrammed or dabbled by your God, and in favour of him creating a free-for-all.-DAVID: Why not think God did it on His own? He would have to pre-program intelligent organisms which is quite a complicated approach compared to direct action by Him. Dabble always is a possibility. (Also, under “amphibious centipede”): DAVID: I admit God could have made cells so intelligent they create new full-blown species, but He would have had to load them with precise programming, which is more complicated than taking direct dabble action. -If he loaded them with precise programming, they would not have had to be intelligent at all! They would be automatons. You are now trying to offload your 3.8-billion-year programme onto my hypothesis! The intelligent cell would NOT be programmed. It has the intelligence to do its OWN inventing. However, I don't mind getting rid of that wretched 3.8-billion-year computer programme of yours, and am delighted to see you at last recognizing its unnecessary complexities. But even if you are now inclined to discard it in favour of dabbling, I'm afraid I still find myself wondering why your God would then personally keep intervening to design the weaverbird's nest, the centipede's underwater apparatus, the cuttlefish's camouflage, and to fiddle with all those different hominins etc., just to create homo sapiens. Something still doesn't quite add up, does it?-dhw: (under “amphibious centipede”): Once again, I can only ask what on earth would be the point of adding complexity just for the sake of complexity? DAVID: It may not be logical to human thought, but the h-p bush shows just that. -You say your God is always in control, and yet in the next breath you have him scattergunning complexities that have no particular purpose other than to be complex! Every innovation (which would add to the complexity by providing something that was not there before) that led to speciation (broad sense) that led to the higgledy-piggledy bush must have functioned in some way, or it would not have survived to become part of the bush. DAVID: All hypotheses are unproven guesses based on what is observed, nothing more, nothing written in stone. Again, what God does may not fit human logic. Until we discover how speciation works, and we may never if it is a result of God's direct action (Saltation), then our hypotheses are moot.-But you are all in favour of logic when you challenge the atheist's faith in chance. It's only when the illogicality of your own hypothesis is exposed that you suddenly deny the value of human logic. Of course all the hypotheses are “moot”. That is why we discuss and test them to try and clarify the issues.
Why sex evolved; no one knows
by David Turell , Wednesday, June 29, 2016, 15:26 (3068 days ago) @ dhw
dhw: Speciation occurs through innovation, and in my version the cells have the intelligence to restructure themselves into new forms. Your God didn't have to “put” anything into that intelligence. Intelligence is enough!-Intelligence has a range of IQ. You proposed cell intel must be 200+ to cause speciation.-> dhw: So if you believe it, it must be true, even though it doesn't make sense even to you. With my hypothesis, there is no need to even try and explain why or how God designed it. He didn't. He enabled the weaverbird to do it. Simple!-See my comments in today's discussion of Higgs.> DAVID: The h-p bush looks scattergun. > > dhw: Like you, I think it is scattergun. But that argues against every new organism and natural wonder being purposely preprogrammed or dabbled by your God, and in favour of him creating a free-for-all.-I don't disagree that it is a possibility through constant saltation/dabbling. > > dhw: I'm afraid I still find myself wondering why your God would then personally keep intervening to design the weaverbird's nest, the centipede's underwater apparatus, the cuttlefish's camouflage, and to fiddle with all those different hominins etc., just to create homo sapiens. Something still doesn't quite add up, does it?-Not for you. Why explain the weaver's nest. See my Higgs comment from today.-> > dhw: You say your God is always in control, and yet in the next breath you have him scattergunning complexities that have no particular purpose other than to be complex! -He may have allowed complexities as I have noted before to eventually reach humans, the most complex organisms on Earth.-> > DAVID: All hypotheses are unproven guesses based on what is observed, nothing more, nothing written in stone. Again, what God does may not fit human logic. Until we discover how speciation works, and we may never if it is a result of God's direct action (Saltation), then our hypotheses are moot. > > dhw: But you are all in favour of logic when you challenge the atheist's faith in chance. It's only when the illogicality of your own hypothesis is exposed that you suddenly deny the value of human logic. Of course all the hypotheses are “moot”. That is why we discuss and test them to try and clarify the issues.-None of my hypotheses are illogical, because logic does not explain God's intentions or plans. Chance is logically disproven! See the Higgs entry.
Why sex evolved; reproduction without sex
by David Turell , Thursday, May 25, 2017, 19:35 (2737 days ago) @ David Turell
Parthenogenesis is well recognized as a female reproductive process. But androgenesis also occurs and even in a vertebrate fish:
http://www.the-scientist.com/?articles.view/articleNo/49504/title/Male-Fish-Borrows-Egg...
"Researchers in Portugal studying a rare type of hybrid fish in the Ocreza River have found an individual that is the exact genomic match to his father. While such androgenesis—the reproduction of a male with no female genetic component—occurs in some non-vertebrates and has been induced in vertebrates artificially, today’s report (May 24) in Royal Society Open Science is the first known description of a vertebrate reproducing this way in the wild.
“'I was very surprised,” said Miguel Morgado-Santos, a graduate student at the University of Lisbon in Portugal who co-authored the study. “I thought maybe it was a mistake and we had captured the father.” But, when the researchers examined the animal’s mitochondrial DNA, which can only be inherited from the mother’s egg, they found that it differed from the father’s. “So, it was definitely an androgenetic individual,” he said.
“'Although [androgenesis] is very rare, there are a number of species out there that do this and . . . it is interesting that people have found it now in a vertebrate,” said evolutionary biologist Laura Ross of the University of Edinburgh who was not involved in the study.
"While the females of many species, including some vertebrates, are well known to be able to reproduce themselves without any input from a male—a process called parthenogenesis—“for a long time, biologists thought that clonal reproduction by males was impossible as they are not able to have babies,” said Ross. However, there are now known to be a handful of species—certain types of ants and fresh water clams, for example—where the “males basically use a surrogate mum to clone themselves,” she said.
"Because there are so few examples of androgenesis, it is not always clear how the phenomenon arises. However, in some species the males are thought to produce sperm with twice the normal genetic content (diploid), and the genetic content of the egg is either absent or eliminated after fertilization. Alternatively, it’s possible that a normal sperm (haploid) can fertilize an egg with either an absent or eliminated genome and the male genome then replicates, or that two sperm can co-fertilize a genome-less egg. Which, if any, of these occurred in the fish is unknown, said Morgado-Santos.
“'In a lot of these cases,” Ross said, “these bizarre types of reproduction seem to have arisen by two closely related species hybridizing at some point in their evolutionary history and something going really, really wrong with reproduction.” Hybridization often results in unmatched chromosome numbers, and consequent sterility of the offspring, she explained, so in essence the reproductive quirks provide a workaround.
"Indeed, the fish that is the subject of the new research—Squalius alburnoides—is the result of a natural hybridization event between another fish, Squalius pyrenaicus, and a now extinct species of the lineage Anaecypris hispanica.
"Members of S. alburnoides are an assorted mix of diploids, triploids and tetrapoids, meaning they carry different combinations and copy numbers of the two genomes of the originator species, explained Morgado-Santos. He and colleagues had been studying an isolated population of S. alburnoides in the hopes of figuring out the complexities of reproduction in these strange fish when, by chance, they found a male offspring that was an exact genomic replica of its father.
"Although the event was clearly rare—just one offspring out of 261 analyzed—“even at a low proportion,” Morgado-Santos said, “this process could be important for hybrid speciation”—the emergence of a new species from the hybrid.
"Indeed, said Tanja Schwander, who studies the evolution of reproductive systems at the University of Lausanne, “we don’t know how these strange reproductive systems evolve . . . and what the steps are from normal sexual reproduction to these unusual systems. These rare spontaneous cases could be a route.”
“'Maybe they could increase [in frequency] gradually and then be coopted into obligate androgenesis,” she suggested, which would genetically isolate the male lineage and create a new species.
"Asexual reproduction is ultimately a risky strategy for a species, as it reduces variation, which might explain the rarity of androgenesis in nature. “In the long term many of these species would go extinct,” Schwander said, but after all, “evolution doesn’t work with foresight.'”
Comment: No one seems to understand how this fits into evolution. It could be a mistake in function.
Why sex evolved; clues in Archaea
by David Turell , Monday, August 15, 2022, 16:37 (830 days ago) @ David Turell
From studies of DNA genes:
https://www.haaretz.com/israel-news/science/2022-08-15/ty-article/sex-cell-fusion-mecha...
"But when, why and in whom did the fusing mechanism first emerge: archaea, bacteria, eukaryotes or possibly even in viruses?
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"Now, a recently published paper in Nature Communications addresses this knotty conundrum. The answer is that fusion genes arose in archaea, the team tentatively concludes.
"The weird thing is that the mechanisms that enable sexual reproduction may have originated in said archaea around 3 billion years ago, which would be a billion years before sex with its fusing gametes emerged,
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"How did they reach this conclusion? Some archaea, they found, contain fusion proteins that turn out to be similar in structure to fusion proteins in eukaryotes and in some viruses. That can hardly be coincidence, but wait for it.
"The team determined the structure of one archaeal fusion protein, Fusexin1, and showed that it is similar in structure to eukaryotic and viral fusexins (while also having regions unique to archaea).
"Also, crucially, the archaeal gene for Fusexin1 has common sequences with “sexual” fusexins in eukaryotes. It was a surprise, Podbilewicz avows.
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"The authors then showed that these archaea proteins can fuse two eukaryotic cells just like fusion proteins in eukaryotes do. The team proved this by introducing the archaea proteins to cultured hamster cells. The hamster cells merged like gametes, they report.
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“'For now, we are sure that archaea have Fusexin1 but not bacteria,” Podbilewicz says. So count bacteria out as fusexin’s daddy.
As for estimating fusion proteins’ origin 3 billion years ago, not all archaea have fusexin – but ones who do live all over the planet, hinting at deep antiquity.
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"Archaea in general are extremophiles, thriving in environments such as the hypersaline Dead Sea in Israel, fumaroles (boiling-hot geysers, deep underground), ice in Antarctica, some living in multiple extremes, and all challenging everything we thought we knew about the limits of life. Their extremophilism is one reason some think they came first because of the extreme conditions on early Earth.
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"For one thing, “the structural similarity is very high, therefore we suggest that all fusexins derived from a common ancestor. Secondly, “the archaeal fusexin1s and the sexual fusexins (HAP2/GCS1) have some similar genetic sequences. This is one of the reasons we think that archaea or eukarya first are currently our preferred hypotheses,” he sums up – but the most parsimonious explanation is that archaea fusexin originated in archaea."
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Comment: It is generally considered that Archaea are the oldest form of life. That they carry the genes and protein for sexual fusion fits with my theory that most of the information for future functions existed in the first living DNA. This fits my form of God, who knows exactly what He wants, makes plans from the beginning, and sets an exact unchanging course. Compare that with dhw's humanized form of God who experiments, changes His mind, and allows free-for-all advances in evolution.