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Science

Biologists Debunk the "Rotting Y Chromosome" Theory 248

Posted by samzenpus from the men-of-the-future dept.
An anonymous reader writes "Biologists have previously predicted that that the male sex-determining Y chromosome, which once carried around 800 genes, like the X, has lost hundreds of them over the past 300 million years, will mutate itself out of existence, leading to the eventual extinction of men. However, researchers of a study published in the latest issue of Nature found evidence to suggest that the Y chromosome will not shed any more of the 19 ancestral genes that it is left with."
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Biologists Debunk the "Rotting Y Chromosome" Theory More

Biologists Debunk the "Rotting Y Chromosome" Theory

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  • I dunno... (Score:4, Funny)

    by owenferguson ( 521762 ) <owenferguson@hot ... minus herbivore> on Wednesday February 22, 2012 @09:29PM (#39132273)
    I tend to shed my genes all over the place ... on the floor, in some Kleenex, in dirty socks...

  • Both sexes are valuable (Score:5, Interesting)

    by Anonymous Coward on Wednesday February 22, 2012 @09:30PM (#39132281)
    While our Y chromosome may make us (men) more susceptible to genetic diseases, it also allows for more rapid adaptation and spread if a mutation is beneficial. I certainly wouldn't want it to go away.

    • Re:Both sexes are valuable (Score:4, Interesting)

      by similar_name ( 1164087 ) on Wednesday February 22, 2012 @09:41PM (#39132363)
      I never quite understood the idea of men going extinct. I'm not a biologist but it seems the last place survival of the fittest is going to stop working is on the first step. I mean once an x chromosome in a male stops functioning it's not going to get passed on. The ones that continue to function will continue to be passed on.

      • Re:Both sexes are valuable (Score:5, Interesting)

        by Darinbob ( 1142669 ) on Wednesday February 22, 2012 @09:49PM (#39132405)

        Except that they were talking about the Y chromosome. The problem with it is that it doesn't get combined with genetic material from the mother, it's passed on as-is. So over time it can degrade due to mutations, and it has done this in the past. However natural selection is strong enough to maintain it.

        • Re:Both sexes are valuable (Score:5, Informative)

          by interkin3tic ( 1469267 ) on Wednesday February 22, 2012 @10:28PM (#39132623)
          Another problem with the y chromesome is that it's not fully redundant with the x chromesome. There are plenty of important genes on the x chromesome that are not duplicated on the y chromesome. There are some diseases which mainly show up in men because females can be heterozygous for it, have one faulty copy but one good copy and be okay. Men on the other hand are hemizygous for genes on the x chromosome. If we get a faulty copy, that's it. We have the disease.
        • I'm interested, why the except? Just because it doesn't get combined with the mother's DNA it really doesn't change the fundamental concepts of evolution. Sure it helps to have to genes to make a protein in case one fails but I don't see that it's required. My understanding is mitochondrial is passed on unchanged. Would there be any reason to suspect it will degrade because of this? The first lifeforms and a lot of life today produces asexually. It doesn't seem to imply a degradation to the point of e
        • Sorry, just noticed I put x chromosome in my original post and that led to the except. Funny how you can reread something and your brain will just keep reading what it expects to see.

        • Re:Both sexes are valuable (Score:5, Interesting)

          by reverseengineer ( 580922 ) on Wednesday February 22, 2012 @11:23PM (#39132993)
          Well, there's no specific reason to favor the XY system of sex determination over some alternative arrangement, like the ZW system in birds (females are ZW, males are ZZ). In that case, the Z chromosome is larger and has more genes than the W. On the other hand, there's really no evidence to suggest that the XY system is any worse than the alternatives, or at least worse enough to support some sort of changeover (or lead to the extinction of placental and marsupial mammals). It does make sense to let Y "rot" to a certain extent: letting Y "cross over" with X is hazardous. It leads to the possibility of producing gametes that contain X chromosomes with male-sex determining genes, and gametes that contain Y chromosomes that lack those male-determining genes. It is to the system's benefit that X and Y are completely non-homologous, even factoring in the problem of X-linked diseases. It's theoretically possible that the function of Y could be captured in a single gene [wikipedia.org]. However, chromosomes are also physical structures that have to be able to be manipulated by the machinery of the cell. It's likely that there is a minimum size for that to be done without high risk of error, which means that Y is safe.... for now.

        • I would contest this, since we are meddling with natural selection with infertility treatments.

          Specifically, the genes on the y chromosome are responsible for healthy sperm and androgen production. Many forms of male infertility are related to malformed sperm, such as sperm with incomplete or otherwise defective acrosomes, tail defects, etc. These can be environmentally caused (had a high fever at one point, or some other non-genetic cause), or they can be genetically caused.

          Modern assisted reproduction te

      • Re:Both sexes are valuable (Score:5, Insightful)

        by __aaltlg1547 ( 2541114 ) on Wednesday February 22, 2012 @11:59PM (#39133213)

        Bingo!

        Humans would have to evolve a new mechanism of determining sex before the Y chromosome could lose its function.

        It's always been obvious that the disappearing Y was bullshit. What we have is a selection pressure that shrinks the Y down to its essential core, which apparently is not much less than the 19 genes and other noncodong DNA it carries in humans.

        • Re:Both sexes are valuable (Score:5, Informative)

          by Anonymous Coward on Thursday February 23, 2012 @02:53AM (#39134001)

          Once again with the subject of genetics on Slashdot, we have a shocking level of confident ignorance on display (aided and abetted by the equally clueless moderators).

          Please, evolution is not synonymous with natural selection. If all you know about genetics is what you learned in Biology 101, perhaps supplemented by a Dawkins book, you're missing out on most of the picture.

          The degeneration of the Y chromosome was made possible by the lack of recombination along most of its length (Muller's ratchet/Hill-Robertson effect), which allowed the combined effects of mutation (including deletions) and genetic drift (which is much stronger on the Y due to there being 1/4 the number of Y chromosomes in a population than a given autosome) to very slowly truncate it. There's really no need to invent post-hoc selective stories to explain this; it's all pretty basic stuff.

          Of course, you are correct that this doesn't mean that males would (or could) go extinct if the Y somehow did disappear. No competent scientist would ever claim this; most likely the sex-determining genes would move to other chromosomes.

          Summary of this story in Nature [nature.com]

          The origins of genome complexity [swarthmore.edu]

    • Re: (Score:2, Insightful)

      by TheGoodNamesWereGone ( 1844118 )
      The comments made me think of this: http://www.psy.fsu.edu/~baumeistertice/goodaboutmen.htm [fsu.edu] . The changing roles of the sexes and modern technology are causing people to honestly ask the question, what are men FOR? As I look back on 50 years of life and 35 years of dating/interacting with females, I wonder too.

  • Rotting Y Chromosome (Score:2, Funny)

    by Anonymous Coward
    It's a common condition afflicting millions of male zombies worldwide.

  • ...shed a tiny tear.

  • Wanted to buy... (Score:5, Funny)

    by Sasayaki ( 1096761 ) on Wednesday February 22, 2012 @09:34PM (#39132315)

    ... go-forward time machine. That way, when Sally McKnight in high school told me, "No way, not if you were literally the last man alive", I can finally test this theory!

    I'm not getting absolutely no sex because I'm a hideous subhuman monster, physically and emotionally... no. I'm doing it for SCIENCE.

  • Seems like a non-issue either way (Score:5, Insightful)

    by alvinrod ( 889928 ) on Wednesday February 22, 2012 @09:39PM (#39132345)
    It really seems like a non-issue regardless of whether or not the Y chromosome is "rotting." Evolution moves slowly enough that by the time it would become an issue, humans will probably have learned enough about genetics to prevent it from happening if necessary. The other alternative is that we decide it's a good idea and speed the process up by a lot.
  • I remember some rabid man-hating feminists really trumpeting the theory that in 100,000 to 2 million years y chromosome would disappear. hah!

  • correct me if I'm wrong (Score:5, Insightful)

    by viperidaenz ( 2515578 ) on Wednesday February 22, 2012 @09:43PM (#39132369)
    But the Y chromosome evolved because sexual reproduction has advantages over asexual reproduction. Until that is nolonger true I can't imagine Y going anywhere.

    • Re:correct me if I'm wrong (Score:5, Informative)

      by samoanbiscuit ( 1273176 ) on Wednesday February 22, 2012 @10:55PM (#39132791)
      No, the XX/XY system of sex determination is just one of the many types used in nature, mostly by mammals. Some animals use the XX(female)/X0(male) system, like ants and bees, while reptiles, birds and some other use the ZZ(male)/ZW(female) system. As you can see, in birds and reptiles (not crocodilians or turtles those have a temperature based sex determination mechanism) the ZZ chromosome configuration (the default) is male, while the ZW configuration causes female development. However, back to the disappearing Y chromosome, it is the fastest mutating chromosome in the human genome (and in all mammalian genomes) because it does not recombine with an analogue chromosome, the way two X chromosomes would. However, just because genes are "lost" does not mean it is shrinking, and research stated here shows it to be the case.

      • Re:correct me if I'm wrong (Score:5, Interesting)

        by Michael Woodhams ( 112247 ) on Wednesday February 22, 2012 @11:40PM (#39133115) Journal

        They Y chromosome not only evolves fast because of lack of recombination, but also because sperm are very many more cell division generations away from the original copy (fertilized ovum) than ova are. The Y chromosome spends 100% of its time in males, normal chromosomes 50%, X chromosomes 33.3%.

        Ref: "Male-Driven Sequence Evolution", pg 225, "Molecular Evolution" by Wen-Hsiung Li (1997).

        • Re:correct me if I'm wrong (Score:4, Interesting)

          by Michael Woodhams ( 112247 ) on Thursday February 23, 2012 @01:45AM (#39133703) Journal

          It just occurred to me that these two effects can be disentangled by looking at birds. The Z chromosome spends 2/3 of its time in males, so should evolve faster than normal (autosomal) chromosome, but it can recombine. The W spends 100% of its time in females, but has no recombination. The 'many times more sperm than ova therefore faster evolution (more errors) in males' may not hold for all animals, but it should hold for birds.

          While I'm at it, I keep pointing out that a cophylogeny of mitochondria and W chromosomes could potentially measure the rate of 'paternal leakage' of mitochondria in a bird species, but so far as I know nobody has tried this.

    • Not all species which use sexual reproduction use an XX/XY system. For example, some species use an XX/XO system where the males have only one copy of the relevant sex chromosome. Other species are completely hermaphroditic. In general, there are a lot of different ways to do sexual reproduction without using an XX/XY system for gender.

    • The Y is not essential to sexual reproduction. There are mammals that have none: the males merely have a single X. Some plants have no sexual chromosomes at all. In some fish sex is controlled by temperature during development.

  • Of course (Score:4, Insightful)

    by aBaldrich ( 1692238 ) on Wednesday February 22, 2012 @09:43PM (#39132371)
    Suppose that someone inherited from his father an Y-Chromosome without the "Manliness Gene". Then he would not have a functioning reproductive system and leave no offspring. The "Manliness Gene" can be lost by a random mutation, but the mutation will never be carried on to the following generation, unless a new sex-determining mechanism already exists.

  • Why would anybody think otherwise? (Score:5, Interesting)

    by Rich0 ( 548339 ) on Wednesday February 22, 2012 @09:44PM (#39132373) Homepage

    So, genders have been around for hundreds of millions of years - why would anybody think that evolution would suddenly make them go away?

    In humans it probably doesn't make so much sense to have lots of sex-linked characteristics, so it makes perfect sense that the contents of the Y chromosome would dwindle over time to just the minimal set of genes necessary to confer gender. After that there should be strong selective pressure to conserve things.

    Suppose for the sake of argument somebody is born with a Y' chromosome that doesn't confer maleness. Either they'll have non-functional reproductive organs, or functional female ones. In the former case they're an evolutionary dead-end. In the latter case and they reproduce with an XY man then 25% of their children will be normal XX females, 25% will be Y'Y offspring that won't make it to birth lacking an X chromosome, 25% will be normal XY males, and 25% will be XY' like the mother. So, in 75% of those cases the Y' chromosome is lost. And all that assumes that there aren't any deformities/etc that make reproduction less likely. I can't see how such a situation could ever become dominant. It would likely reach some low frequency equilibrium even if not harmful.

    The fact that it hasn't already happened makes me think that it is not likely to do so.

    • It is pretty obvious that +99% of the genes that express male characteristics are not in the Y chromosome. For all that matters the Y chromossome could have just a single gene.
      is_male = True

    • Re: (Score:2)

      by Luckyo ( 1726890 )

      It's worth noting that XY is not the only combination to result in a male part of species. There are species where XY is female and XX is male, and myriad of more complex variations.

      Finally there are species based on hermaphroditism (each individual carries both sets of reproductive organs). Notably this conditions is sometimes (rarely) manifested in humans as well, however due to our genetic and fysiological layout hermaphrodites are rarely if ever capable of sexual reproduction as more then their one "pri

    • Re:Why would anybody think otherwise? (Score:5, Informative)

      by FrootLoops ( 1817694 ) on Thursday February 23, 2012 @12:56AM (#39133485)

      It's worth noting that conditions apart from standard XX female and XY male do occur in humans:

      Turner syndrome [wikipedia.org]: usually, single X chromosome, no second X or Y. Creates females who are almost always infertile with varying physical problems. Incidence is around 1 in 2000 to 1 in 5000 (phenotypic) females.
      Triple X syndrome [wikipedia.org]: XXX chromosomes. Makes females with essentially no physical differences from XX females (including reproductively). Incidence: 1 in 1000 females.
      Klinefelter's Syndrome [wikipedia.org]: XXY chromosomes. Produces sometimes-infertile males, sometimes with developmental problems. 1 in between 500 and 1000 males affected.
      XYY Syndrome [wikipedia.org]: XYY chromosomes. Almost no physical differences with XY males (slightly taller). 1 in 1000 males.
      XX Male Syndrome [wikipedia.org]: XX chromosomes. Produces always-infertile males who usually appear to be XY males. 4 or 5 in 100,000 people.
      Swyer Syndrome [wikipedia.org]: XY chromosomes. Produces females without developed gonads, though a developed uterus may be able to carry another person's embryo.

      The above is only a partial list. There are quite a few related conditions that fall under the general heading of "Intersex [wikipedia.org]" (sometimes you see the acronym LGBTI; that's the I). They vary widely from producing (some type of) hermaphrodites to causing a large number of non-standard sex characteristics. From the article,

      According to Fausto-Sterling's definition of intersex, on the other hand, 1.7 percent of human births are intersex.

      and

      Between 0.1% and 0.2% of live births are ambiguous enough to become the subject of specialist medical attention, including surgery to disguise their sexual ambiguity.

      To give a very approximate comparison (these numbers vary a lot by region, time period, and definition), around 1% of the population is bisexual, and around 5% is gay. It's perhaps even more difficult to get an accurate transgender incidence number; I've seen between 0.2% and 0.003%. Those who get sex reassignment surgery are in the minority. (There's a lot more to gender than the type of gonads you have, and female-to-male surgery isn't terribly effective.)

      • Re:Why would anybody think otherwise? (Score:4, Informative)

        by FrootLoops ( 1817694 ) on Thursday February 23, 2012 @08:59AM (#39135537)

        Since the info above was informative, here are a few other statistics that interest me and help put minority issues into perspective. They're at best tangentially related to TFA, though.

        There are perhaps 100,000 furries in the US, or around 1 in 3000 people. [Furries at a glance [google.com]: the majority are young white men; they're pretty much evenly split between hetero and homosexual, with many at varying degrees of bisexuality; very few own fursuits; to be clear, furries primarily have an interest in anthropomorphic characters, so "it's not about sex" (though as always it can be).]

        30% of those over 24 in the US [wikipedia.org] have a bachelor's degree. Only 3% have doctorates or professional degrees.

        Around 25% of all people in Swaziland have HIV/AIDS [wikipedia.org]. The number jumps to over 50% for women 25-29. [Yes, this is unbelievably tragic.] Around 0.4% of the US population has HIV/AIDS, though around 20% of men who have sex with men do [cdc.gov] (accounting for around half of all cases; receptive anal sex spreads it more quickly than any other common sex practice; interestingly, fellatio is almost entirely safe in this regard; condoms reduce transmission rates by only ~80%, depending on specifics).

        Around 1% of the US population is some variety of Native American [wikipedia.org]. Around 15% are poor [wikipedia.org].

  • What were they thinking? (Score:3)

    by macraig ( 621737 ) <mark@a@craig.gmail@com> on Wednesday February 22, 2012 @09:45PM (#39132375)

    The others that were lost simply weren't necessary to the male role; it was a streamlining process to make us lean and mean procreative machines. It's not like all the males conceived at those earlier times suddenly and simultaneously lost one... it was a gradual overlapping process. It was... EVOLUTION. Go figure!

    • exactly, we just need genes that encode for a cock-n-balls, and genes that allow us to open stuck jars and reach high objects.

  • I guess metrosexuals, hipsters, emo kids, and several other groups were never in any danger in the first place...

  • link to the source, please (Score:5, Informative)

    by rritterson ( 588983 ) on Wednesday February 22, 2012 @09:47PM (#39132391)
    Not like I love the Nature Publishing Group (NPG) very much, but let's link to the source to help give the original authors credit. (Which, as far as I can tell, the medical daily article doesn't even do!)

    Here is a link to the original paper [nature.com]

    For those who aren't molecular biologists or geneticists, here is a link to the Nature news article [nature.com] on the scientific paper

    • That's because the original paper asks you to pay $32 to view it unless you are subscribed[or your IP is subscribed ie by your University]. A subscription is $199 a year.

  • Who actually thought that? Why? (Score:4, Informative)

    by Suddenly_Dead ( 656421 ) on Wednesday February 22, 2012 @09:48PM (#39132399)

    If I search for "rotting y theory", all I get are variations of this article. Why would anyone who knows anything about evolution and genetics actually think that? And who were these people?

    • wasn't really called that, you can look for "y chromosome degeneration" http://www.physorg.com/news167026463.html [physorg.com]

  • I don't think a theory suggesting the extinction of males just because the y chromosome is small is sufficiently prevalent to require debunking. If so the state of science is far worse than I had imagined...

    • no, those theories were instead based on the known degeneration over time of Y. what this study shows is that the degeneration, once exponentially fast, keep to a skidding halt in our immediate primate ancestors

      • Re: (Score:2)

        by Junta ( 36770 )

        I was under the impression the general understood consensus is that generally in evolution, usually past performance is not a reliable indicator of future events. If there is no selection pressure at work, things randomly vary one way or another and those variances 'just are'. There seems to be some popular desire for evolution to have some sort of will, some predictable course where toes dissolve and brains get bigger because we perceive toes as useless and brains as good. The grade of evolution is sim

    • I think that the scientists understand that the disappearence of the Y chromosome does not mean the disappearence of men. The reporters, on the other hand...

  • Where did you get that ridiculous idea?

  • Just finished teaching the units on male and female sexual development at a major medical school last week. Even my students know that you need part of the human Y chromosome (SRY gene) to make testes differentiate from primordial gonad tissue. It also makes the 'pre-Fallopian tubes' and what would become uterus and much of vagina (Mullerian duct system) "go away" in developing male fetuses. If SRY gene "jumps" to another chromosome, you don't get proper differentiation of gonads and genitalia. No SRY, g

    • I think that the assumption is that those genes would move elsewhere and other mechanisms would develop to control differentiation. Other lifeforms manage it.

      • Re: (Score:2)

        by Junta ( 36770 )

        The question being what would be the mechanism to drive such a change. Just because we want to create a pattern doesn't mean we can absent of some scientific explanation as to why that would be the case.

        • The question being what would be the mechanism to drive such a change.

          The point of the article seems to be that the change is not ocurring.

        • Re:Y ain't going' nowhere - makes testes (Score:5, Informative)

          by reverseengineer ( 580922 ) on Thursday February 23, 2012 @01:32AM (#39133647)
          It appears to have already happened in a few species; as the Nature News article notes, a few rodents have lost their Y chromosome completely. These remain capable of sexual reproduction and also remain differentiated between male and female. In some cases, this was the result of a permanent translocation of the SRY gene to another chromosome- either Y or a somatic chromosome. In some cases, SRY is completely lost, and different genes are used for sex determination. There's really nothing extraordinary about SRY itself, a gene thought to be an accidental duplication of an existing gene on the X [febsletters.org]. It may well be the case that how an organism determines its sex simply doesn't matter enough; there just has to be some consistent system that allows for propagation of the species. There's a wide variety of successful systems out there already coexisting, and given millions more years, undoubtedly more systems would pop up. In the case of the Y chromosome, however, it was not certain that the system could reach a stable equilibrium at all- it has lost over 96% of its genes in the course of its existence, and it faces an essential problem: the long-term selection to protect reproduction by isolating itself from recombination with X also increases its vulnerability. Ironically, the Y chromosome is itself "asexual" in a way- it passes from father to son through generations without being modified by recombination. Errors tend to accumulate, deletions cannot be replaced- it's called Muller's ratchet. Eventually, XY organisms would need to make alternative arrangements or go extinct.

          It would appear, however, that Y chromosomes are a bit more robust than originally thought, and may be able to continue at their present level of basic function for tens of millions of years more. Just as my own thought, one reason for this may be the presence of genes on the Y which are necessary for sperm production. A transition to another form of sex determination would require those genes to be either moved or their functionality replaced elsewhere; otherwise any Y-less males would be azoospermic and therefore the new system wouldn't get passed on.

  • Some women think... (Score:5, Funny)

    by gstrickler ( 920733 ) on Wednesday February 22, 2012 @11:07PM (#39132881)

    ...the Y chromosome is already rotten.

  • Well, I guess I can stop work on my time machine, they won't be needing me for insemination like I'd hoped.

  • ... to kill spiders.

  • Reducing size is one thing, degenerating down to nothing makes no sense. Sexual reproduction is still going strong after 500 or 600 million years.

    I reminded of the "prediction" that Pluto, will all the downward recalculations of its mass since its discovery, would end up with negative mass and negative volume by mid 21st century.

  • The Far Side (Score:4, Funny)

    by guttentag ( 313541 ) on Thursday February 23, 2012 @12:39AM (#39133431) Journal
    Back in the day there was a Far Side cartoon of a cave man forming cylinder-like shapes with his hands, holding them to his eyes like binoculars and staring intently at the table in front of him. The caption read: Prehistoric Microbiologists. I always thought: "Stupid caveman! He can't see anything." Now I realize he was staring at a Y chromosome... Because it would have been that much larger in his day.

  • Never understood that concern (Score:5, Insightful)

    by Arancaytar ( 966377 ) <arancaytar.ilyaran@gmail.com> on Thursday February 23, 2012 @02:07AM (#39133807) Homepage

    What is so worrying about a chromosome becoming smaller over millions of years? If any of the genes that were on it were vital to humans, we wouldn't be here (or rather, they wouldn't have disappeared, since their absence would have been selected against). And what's with the extrapolation - can you really take a past evolutionary trend and use it to project future changes?

    If that worries you, how about this: Within a much smaller time frame, our fur has disappeared, our bones and skin have become thinner and our brains have grown. If that trend continues, then eventually we'll have no bones or skin, and our brains will be too big for our bodies to carry.

  • Men were never going extinct (Score:3)

    by reve_etrange ( 2377702 ) on Thursday February 23, 2012 @03:33AM (#39134179)

    ...mutate itself out of existence, leading to the eventual extinction of men

    That is unscientific hyperbole. The probable long term outcome of genes disappearing from the Y chromosome is that it would only carry the sex determination (SRY) gene, which is just what has already happened in Kangaroos. After that point, further evolution might lead to an entirely new system of sex determination, such as those arising in some species of vole.

    Even for rapidly evolving systems such as the SRY gene, Y chromosome and any replacement system, these changes take millions of years. There's no reason to believe that men, or whatever we are calling them then, will suddenly disappear, leaving the species unable to reproduce without technologically induced parthenogenesis.

    ...but we can still dream.

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