This PR is ridiculously unscientific. This doesn't "prove" their hypothesis. They've found no mechanism of action meaning they found a correlation. Correlation is not causation. Maybe the actual study found something more than the PR says but it doesn't seem like it. Also, they called it the "holy grail". Seriously?
As the Stanford article said, this is "one of the holy grails" in its field because it has been an open question for decades. It was hypothesized but never observed, because collecting the data - multigenerational family histories of animals - is quite hard.
The researchers found a clever way by analyzing zoo animals, which do have records. It still took years of work though.
Of course they didn't "prove" anything. But you are setting a ridiculously high bar for scientific progress, which is generally very incremental. They took an open question that was undecided for decades and found a way to collect a large amount of data to support the hypothesis. Now that that is - finally! - done, work can proceed to focus on the mechanism.
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.
I thought I've read other papers where a mechanism was both proposed and observed. Selective abortion - female mammalian bodies will abort fetuses in the early months of pregnancy when environmental conditions indicate that offspring don't stand a good chance of survival. IIRC the paper I read showed this happened in mice, but it's known that in humans a large number of women will miscarry in the first 1-2 months of pregnancy, and it may be the same mechanism at work there.
Hamilton [2], focused on scenarios specific to particular insect groups. In Mammals and birds a more general principle applies: the number of offspring a male produces is often limited by how many females he can mate with, while a female is limited by how many offspring she can physiologically produce [5], [6].This generates a tendency for males to vary more in first-generation success than females. Thus male offspring are a high-risk-high-reward bet for potential grandparents in the genetic lottery; while females are a safe, hedged bet [5], [6]. However, just like in insects, if a grandparent ‘knows’ that a male offspring is a low-risk-high-reward bet, then they can beat the house, and hit a jackpot (in terms of grandchildren produced) [5], [6]. Furthermore, grandparents can beat the house in other more subtle ways, leading later authors to propose a variety of advantages to SR manipulation that might apply to vertebrate species (e.g. local resource competition or enhancement [3]).
some basic background from the paper. lets try and drag the level of debate up a little here?
Some of the worst science reporting I've ever read. That said, after reading the journal article itself, I found plenty of false assumptions there as well.
"... if functional consequences of SR manipulation were to be found in mammals, then it would suggest that mammals (either in individual species, or in general), possess unknown physiological mechanisms to control birth SR."
This sentence in the introduction assumes a level of choice on the part of the mammals that is pervasive in the article but never substantiated or even formalized to the point of a testable hypothesis. It is the type of sloppy science that takes away from the truth, and it's becoming way too common. It's as if scientists feel that if they just have some good hard numbers, they get the freedom to toss conjecture around as Theory for a few paragraphs.
The study found that gender bias in birth rates can affect the number of grandchildren. That is the takeaway here. No evidence whatsoever of what caused that bias is present, nor do I accept their statement that the study taking place in a zoo means that their findings are somehow more likely to be present in the wild. That would require a different experiment on its own.
> This sentence in the introduction assumes a level of choice on the part of the mammals that is pervasive in the article but never substantiated or even formalized to the point of a testable hypothesis.
The field here is evolutionary biology, and specifically the area of parental investment and applications of game theory. It is very common in that area to talk about "choice" etc. while not meaning anything conscious. For example, it is acceptable to say that genes "want" to propagate copies of themselves, but of course this is just shorthand for something very different. In the field, this is not misunderstood, it is the norm.
> The study found that gender bias in birth rates can affect the number of grandchildren.
No, the point was that they found that gender bias in birth rates appeared to be not entirely random (50-50) and weighted towards what generates an optimal number of grandchildren. That exactly supports a hypothesis that has been around for decades that through female choice (again, choice is not meant in the sense that I can choose what to eat for lunch), animals can affect gender birth ratios in order to maximize the number of grandchildren. (Here you can see the connection to game theory.)
It is very hard to study that empirically, which is why this study is receiving a lot of attention - after decades, it is among the first to actually give measurements.
> nor do I accept their statement that the study taking place in a zoo means that their findings are somehow more likely to be present in the wild. That would require a different experiment on its own.
This is indeed a weakness in their methodology, and surely being debated heavily.
I think the interesting finding is that the biases in sex ratio were towards the more successful sex. That is, if A has more sons than daughters, each of those sons has more offspring on average than other males. But if A has more daughters than sons, each of those daughters has more offspring than other females. That implies that the bias is adaptive: whatever is causing it, it is maximising the number of grandchildren A has.
Also, I don't see any problem with conjecture in scientific papers.
All that is being discovered is that sons mean more grandchildren, and a few groups (billionaires, top-ranking wives) are cherry-picked because they have more sons. Dung flies are mentioned but they are not even mammals, and they aren't sex selecting their sperm.
That said, though the article claims a mechanism is unknown, diet can influence whether a girl or boy is conceived:
My own wild guess is that the observed diet factors, or at least certain states of the body that diet can cause, account for any statistically significant distributions of sex, not a mysterious sperm-guiding mechanism.
Or, perhaps better, here: http://med.stanford.edu/ism/2013/july/ratios.html -- this being where ScienceDaily copied it from. (There's actually a tiny bit of extra information in the Stanford version, namely its last sentence.)
[+] [-] driverdan|12 years ago|reply
This PR is ridiculously unscientific. This doesn't "prove" their hypothesis. They've found no mechanism of action meaning they found a correlation. Correlation is not causation. Maybe the actual study found something more than the PR says but it doesn't seem like it. Also, they called it the "holy grail". Seriously?
[+] [-] azakai|12 years ago|reply
The researchers found a clever way by analyzing zoo animals, which do have records. It still took years of work though.
Of course they didn't "prove" anything. But you are setting a ridiculously high bar for scientific progress, which is generally very incremental. They took an open question that was undecided for decades and found a way to collect a large amount of data to support the hypothesis. Now that that is - finally! - done, work can proceed to focus on the mechanism.
[+] [-] venomsnake|12 years ago|reply
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.
[+] [-] nostrademons|12 years ago|reply
[+] [-] Tloewald|12 years ago|reply
[+] [-] andrewcooke|12 years ago|reply
some basic background from the paper. lets try and drag the level of debate up a little here?
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...
[+] [-] jamestomasino|12 years ago|reply
"... if functional consequences of SR manipulation were to be found in mammals, then it would suggest that mammals (either in individual species, or in general), possess unknown physiological mechanisms to control birth SR."
This sentence in the introduction assumes a level of choice on the part of the mammals that is pervasive in the article but never substantiated or even formalized to the point of a testable hypothesis. It is the type of sloppy science that takes away from the truth, and it's becoming way too common. It's as if scientists feel that if they just have some good hard numbers, they get the freedom to toss conjecture around as Theory for a few paragraphs.
The study found that gender bias in birth rates can affect the number of grandchildren. That is the takeaway here. No evidence whatsoever of what caused that bias is present, nor do I accept their statement that the study taking place in a zoo means that their findings are somehow more likely to be present in the wild. That would require a different experiment on its own.
[+] [-] azakai|12 years ago|reply
The field here is evolutionary biology, and specifically the area of parental investment and applications of game theory. It is very common in that area to talk about "choice" etc. while not meaning anything conscious. For example, it is acceptable to say that genes "want" to propagate copies of themselves, but of course this is just shorthand for something very different. In the field, this is not misunderstood, it is the norm.
> The study found that gender bias in birth rates can affect the number of grandchildren.
No, the point was that they found that gender bias in birth rates appeared to be not entirely random (50-50) and weighted towards what generates an optimal number of grandchildren. That exactly supports a hypothesis that has been around for decades that through female choice (again, choice is not meant in the sense that I can choose what to eat for lunch), animals can affect gender birth ratios in order to maximize the number of grandchildren. (Here you can see the connection to game theory.)
It is very hard to study that empirically, which is why this study is receiving a lot of attention - after decades, it is among the first to actually give measurements.
> nor do I accept their statement that the study taking place in a zoo means that their findings are somehow more likely to be present in the wild. That would require a different experiment on its own.
This is indeed a weakness in their methodology, and surely being debated heavily.
[+] [-] takluyver|12 years ago|reply
Also, I don't see any problem with conjecture in scientific papers.
[+] [-] brass9|12 years ago|reply
[+] [-] 1123581321|12 years ago|reply
That said, though the article claims a mechanism is unknown, diet can influence whether a girl or boy is conceived:
http://genderdreaming.com/2011/05/the-french-gender-diet/
http://www.rbmojournal.com/article/S1472-6483(10)00549-3/abs...
My own wild guess is that the observed diet factors, or at least certain states of the body that diet can cause, account for any statistically significant distributions of sex, not a mysterious sperm-guiding mechanism.
[+] [-] gjm11|12 years ago|reply
Or here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna... -- this is the journal article it's all about, and reports the research in much more detail.
[+] [-] randartie|12 years ago|reply
[+] [-] clubhi|12 years ago|reply
[+] [-] unknown|12 years ago|reply
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