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Actually I thought of very fun experiment - because the gender of the baby is determined by the father - make two groups live in extreme condition bio-dome styl

Actually I thought of very fun experiment - because the gender of the baby is determined by the father - make two groups live in extreme condition bio-dome style for a month or two - 900 males and 100 females and in the other 100 males and 900 females in the second. Then at the end of the period just examine the ratio of sperm cells with X and Y chromosome in the males' semen. If there is sizable difference means there are mechanisms for regulation and selection. Anecdotal evidence is that even after very bloody wars where the males die off disproportionately the population does not stray off a lot in the gender balance after a few years. Bonus points if you make it with humans as reality TV on Bravo.

dllthomas 13y ago
The hypothesis here is that it is not the father that determines the gender of the baby.
- venomsnake 13y ago
  The father determines the gender in a sense that he provides both X and Y. The woman only provides X. In the facts given in the article I found nothing convincing that the gender selectors are females i.e. they conclude that they are. Now I haven't studied seriously biology but to change the meiosis of sperm cells to skew the odds seems more effective (and simple) than to have the egg cell select the sperm with the X or Y chromosome during the fertilization that is messy as it is. And if X and Y sperm cells were somehow different I think we may have found out.
  - dllthomas 13y ago
    > The father determines the gender in a sense that he provides both X and Y. The woman only provides X. That's not a meaningful sense. Obviously it's a question of whether a sperm cell carrying an X or Y chromosome gets into the egg, but both parties have a lot of biology involved between meiosis and fertilization that might impact that. > Now I haven't studied seriously biology but to change the meiosis of sperm cells to skew the odds seems more effective (and simple) than to have the egg cell select the sperm with the X or Y chromosome during the fertilization that is messy as it is. And if X and Y sperm cells were somehow different I think we may have found out. X and Y sperm cells are different - one is carrying an X and the other is carrying a Y and these will therefore have different masses and probably some other characteristics will differ. As female mammals tend to invest hugely more resources in the individual child, it's more likely to be worthwhile to them to sacrifice some chance of conception to favor a particular gender. Furthermore, if the child is more likely to stay with the female, the female is a better predictor of the environment the child will be raised in. Since meiosis produces an X and Y cell inherently (it splits a cell with an X+Y in half, with one chromosome going each way) and furthermore happens well in advance of mating when the partner may not even be determined, it seems less likely that the cause for any pattern in SR would be manipulation of the ratio of X vs Y cells during meiosis. Of course, biology surprises on occasion, I just think you're making entirely unwarranted assumptions.
    - craigyk 13y ago
      Still the mechanisms by which the male body might control the ratio of sperms with X vs. Y is astoundingly simpler than mechanisms by which an egg can somehow "sense" and reject sperm. On the other hand, a mechanism by which the female body can selectively abort an embryo is way more plausible. Either way, this leads to some pretty testable predictions. You might not even need to do much direct experimentation, an outcome of the second hypothesis is that if gender selection is highly activated than more eggs/embryos are wasted, which might lead to smaller litters/ longer time between pregnancies.
      - dllthomas 13y ago
        > mechanisms by which an egg can somehow "sense" and reject sperm. Evolution doesn't work like an engineer. If you or I were going to sit down and say, "Hmm, how do we control the sex ratio from within the female's body?" we'd come up with things like a mechanism to differentiate the sperm and then try to apply that to a mechanism to block or help one group or the other, because modularity is good and such. Evolution doesn't pay attention to the mechanism, just the result. Maybe it happens that one type of sperm is disproportionately affected by acidity levels or viscosity of cervical mucous or any of potentially hundreds of attributes of the environment the sperm will be encountering between meiosis and conception, and that's assuming any differentiation happens pre-conception. If there is such an effect, there's a good chance evolution will "spot it" and exploit it where the gain outweighs the cost; the female has (evolutionarily speaking) far more motivation to make use of it, if it involves any tradeoff with chance of conception. Note that by his hypothesis, smaller litters or longer time between pregnancies probably is what you'd see if the decision was being made in the female's body, whether pre- or post-conception.
        dllthomas 13y ago
        s/by his hypothesis/by this hypothesis/
  - nostrademons 13y ago
    Not all babies that are conceived are born. If the woman's body proves inhospitable to the developing fetus, they could easily skew the sex ratio without skewing the sex of any one individual child.
  - samuel 13y ago
    Men with higher testosterone levels are more likely to produce male offspring. So I agree with you. It seems easier to put the gender bias mechanism in the males.
    - dllthomas 13y ago
      Don't use humans for your reasoning here - we have a lot of trouble doing controlled studies. In particular, the statement "men who have higher testosterone levels are more likely to produce male offspring" is pretty much equivalent to the statement "women having sex with men who have higher testosterone levels are more likely to produce male offspring", unless it was measured by impregnating women in a double-blind setting. If it was based on conceptions from a sperm bank, it might be better evidence, though my understanding is they still generally report some information to the women about potential fathers and give her some choice in the matter (but I could easily be mistaken, there).
newnewnew 13y ago
Nitpick: the technical term here would be "sex", not "gender". "Gender" seems to be used as an animal's social-sexual identity, whereas "sex" is an animal's actual biological reproductive sex. The word "gender" was originally linguistic, for example it was used to refer to the gender of spanish nouns. The use of "gender" to describe one's social-sexual role was popularized by the feminist movement in the 70s, who believed that social distinctions based on sex are largely arbitrary. Anyways, gender is a fairly modern term and it certainly doesn't refer to the sex of an animal. Although, for most animals I would guess that their gender and sex are the same, unless sexual camouflage is used in that species as a reproductive strategy. Humans are unique in divorcing sex (and gender) from reproduction.
- azakai 13y ago
  > "Gender" seems to be used as an animal's social-sexual identity That has changed. You can now find many studies in biology talking about the gender of animals (frogs, insects, anything) when they literally mean what you refer to as sex here. > Humans are unique in divorcing sex (and gender) from reproduction. That is highly speculative. We do not understand animals well enough to even know if that is a meaningful question.
Peaker 13y ago
Why do you think it is necessarily much simpler? Selecting X or Y sperm cells may be easy, if there is some sort of external effect to the genes in those. For example, perhaps X causes sperm cells to be more robust to acidity, and the female can select for X by increasing acidity levels.
- venomsnake 13y ago
  Well ... mostly because we haven't found yet such difference (that I know of) and sperm has been thoroughly studied. IVF in humans can be very telling if number crunched properly - the eggs are extracted and the mother body is out of the equation for a moment. Now if the sex selection/discrimination is population based - it is simpler and easier to make it in the males. If it is per embryo - than you have no choice but make it in the females no matter how complex.

dllthomas 13y ago

The hypothesis here is that it is not the father that determines the gender of the baby.

venomsnake 13y ago
The father determines the gender in a sense that he provides both X and Y. The woman only provides X. In the facts given in the article I found nothing convincing that the gender selectors are females i.e. they conclude that they are. Now I haven't studied seriously biology but to change the meiosis of sperm cells to skew the odds seems more effective (and simple) than to have the egg cell select the sperm with the X or Y chromosome during the fertilization that is messy as it is. And if X and Y sperm cells were somehow different I think we may have found out.
- dllthomas 13y ago
  > The father determines the gender in a sense that he provides both X and Y. The woman only provides X. That's not a meaningful sense. Obviously it's a question of whether a sperm cell carrying an X or Y chromosome gets into the egg, but both parties have a lot of biology involved between meiosis and fertilization that might impact that. > Now I haven't studied seriously biology but to change the meiosis of sperm cells to skew the odds seems more effective (and simple) than to have the egg cell select the sperm with the X or Y chromosome during the fertilization that is messy as it is. And if X and Y sperm cells were somehow different I think we may have found out. X and Y sperm cells are different - one is carrying an X and the other is carrying a Y and these will therefore have different masses and probably some other characteristics will differ. As female mammals tend to invest hugely more resources in the individual child, it's more likely to be worthwhile to them to sacrifice some chance of conception to favor a particular gender. Furthermore, if the child is more likely to stay with the female, the female is a better predictor of the environment the child will be raised in. Since meiosis produces an X and Y cell inherently (it splits a cell with an X+Y in half, with one chromosome going each way) and furthermore happens well in advance of mating when the partner may not even be determined, it seems less likely that the cause for any pattern in SR would be manipulation of the ratio of X vs Y cells during meiosis. Of course, biology surprises on occasion, I just think you're making entirely unwarranted assumptions.
  - craigyk 13y ago
    Still the mechanisms by which the male body might control the ratio of sperms with X vs. Y is astoundingly simpler than mechanisms by which an egg can somehow "sense" and reject sperm. On the other hand, a mechanism by which the female body can selectively abort an embryo is way more plausible. Either way, this leads to some pretty testable predictions. You might not even need to do much direct experimentation, an outcome of the second hypothesis is that if gender selection is highly activated than more eggs/embryos are wasted, which might lead to smaller litters/ longer time between pregnancies.
    - dllthomas 13y ago
      > mechanisms by which an egg can somehow "sense" and reject sperm. Evolution doesn't work like an engineer. If you or I were going to sit down and say, "Hmm, how do we control the sex ratio from within the female's body?" we'd come up with things like a mechanism to differentiate the sperm and then try to apply that to a mechanism to block or help one group or the other, because modularity is good and such. Evolution doesn't pay attention to the mechanism, just the result. Maybe it happens that one type of sperm is disproportionately affected by acidity levels or viscosity of cervical mucous or any of potentially hundreds of attributes of the environment the sperm will be encountering between meiosis and conception, and that's assuming any differentiation happens pre-conception. If there is such an effect, there's a good chance evolution will "spot it" and exploit it where the gain outweighs the cost; the female has (evolutionarily speaking) far more motivation to make use of it, if it involves any tradeoff with chance of conception. Note that by his hypothesis, smaller litters or longer time between pregnancies probably is what you'd see if the decision was being made in the female's body, whether pre- or post-conception.
      - dllthomas 13y ago
        s/by his hypothesis/by this hypothesis/
- nostrademons 13y ago
  Not all babies that are conceived are born. If the woman's body proves inhospitable to the developing fetus, they could easily skew the sex ratio without skewing the sex of any one individual child.
- samuel 13y ago
  Men with higher testosterone levels are more likely to produce male offspring. So I agree with you. It seems easier to put the gender bias mechanism in the males.
  - dllthomas 13y ago
    Don't use humans for your reasoning here - we have a lot of trouble doing controlled studies. In particular, the statement "men who have higher testosterone levels are more likely to produce male offspring" is pretty much equivalent to the statement "women having sex with men who have higher testosterone levels are more likely to produce male offspring", unless it was measured by impregnating women in a double-blind setting. If it was based on conceptions from a sperm bank, it might be better evidence, though my understanding is they still generally report some information to the women about potential fathers and give her some choice in the matter (but I could easily be mistaken, there).

newnewnew 13y ago

Nitpick: the technical term here would be "sex", not "gender". "Gender" seems to be used as an animal's social-sexual identity, whereas "sex" is an animal's actual biological reproductive sex. The word "gender" was originally linguistic, for example it was used to refer to the gender of spanish nouns. The use of "gender" to describe one's social-sexual role was popularized by the feminist movement in the 70s, who believed that social distinctions based on sex are largely arbitrary. Anyways, gender is a fairly modern term and it certainly doesn't refer to the sex of an animal. Although, for most animals I would guess that their gender and sex are the same, unless sexual camouflage is used in that species as a reproductive strategy. Humans are unique in divorcing sex (and gender) from reproduction.

azakai 13y ago
> "Gender" seems to be used as an animal's social-sexual identity That has changed. You can now find many studies in biology talking about the gender of animals (frogs, insects, anything) when they literally mean what you refer to as sex here. > Humans are unique in divorcing sex (and gender) from reproduction. That is highly speculative. We do not understand animals well enough to even know if that is a meaningful question.

Peaker 13y ago

Why do you think it is necessarily much simpler? Selecting X or Y sperm cells may be easy, if there is some sort of external effect to the genes in those. For example, perhaps X causes sperm cells to be more robust to acidity, and the female can select for X by increasing acidity levels.

venomsnake 13y ago
Well ... mostly because we haven't found yet such difference (that I know of) and sperm has been thoroughly studied. IVF in humans can be very telling if number crunched properly - the eggs are extracted and the mother body is out of the equation for a moment. Now if the sex selection/discrimination is population based - it is simpler and easier to make it in the males. If it is per embryo - than you have no choice but make it in the females no matter how complex.