why does gender run in families?

[Lilian78]

I don't generally believe in swaying . . . but in considering ttc #4, I'm open to the idea of at least considering it. And the thing that kind of convinces me is that gender seems to run in families. I know virtually no one with an evenly balanced family. Is this just how the 50/50 odds play out? Just wondering what you guys think about this phenomenon/whether you've observed the same. Is it unintentional swaying (maybe people's habits) factoring in, or is it just chance?:confused:

[nuthinbutpink]

One of the biggest studies of families for trying to determine if gender runs in fmailies was done in 1979- called the National Longitudinal Study of Youth conducted by the US Department of Labor. They took a sample of 12,686 men and women from 14-22 years of age. They followed them through current day and still interview them on a bunch of different topics bianually.

Then, a lady that was interested in this topic wrote a magazine article in 2001. She went through all of the data they collected and pulled out the family/gender information and analyzed it Here are the findings:

NLSY Families by Number of Children

1 Child 1,881 31%
2 Children 2,444 40%
3 Children 1,301 21%
4+ Children 463 8%
Total Families 6,089

Total Boys/Girls in NLSY Families
Boys 6,389 51%
Girls 6,135 49%
Total 12,524

So, although there were families, obviously that had all boys or all girls they could not find any proof via statistics that gender ran in families.

When I started reading about swaying, I needed the science behind it, the studies, that showed that either it made a difference or not. There is a study in the Dream member access forums(where chat is) where there is a Science Direct study that studied diet and timing and the effect on gender. It was done by a lady that runs a company that "helps" people with diet/timing, tests their blood, etc. she was kind of selling something and the data comes from her people. It is interesting though. The whole thing is there if you would like to read it.

[atomic sagebrush]

Here's a link to the article that NBP is talking about (I haven't read this one yet but my mouth is watering!) Looks like it concludes that boys or girls do NOT run in families.

http://www.isds.duke.edu/~dalene/chance/chanceweb/144.rodgers.pdf

This study went back and counted actual boys or girls born over several generations in family trees. This study DID conclude that boys/girls DO run in families.

http://www.sciencedaily.com/releases/2008/12/081211121835.htm

I elaborated a bit on that study here - http://genderdreaming.com/forum/showthread.php?467-GUESS-WHAT-MEN-MAKE-50-50-X-AND-Y-SPERM!!!&p=2492#post2492

[nuthinbutpink]

It's funny because the woman that wrote that original article, there were all boys for several generations in their family and then within her husband's and his brother's generation, they had 4 girls and 1 boy between the two families after all those boys.

Very interesting about the genes.

[atomic sagebrush]

Now - I DO NOT believe gender "runs in families"...exactly. I do not and will never believe for one minute that there is a "boy gene" or a "girl gene" that either man or woman carries (and I will write an essay about this to explain why in depth).

What I DO believe is that ALL people everywhere have some sort of mechanism that sizes up their environment and "decides" on the basis of that, whether a boy or a girl has a better shot at survival and successful growth to reproductive ages. Since families oftentimes share the same environment (or at the very least did during their formative years), it seems reasonable to conclude that some families will have indeed more of one gender than would be statistically expected based on this shared environment. But obviously, even in the same family, siblings' experiences can and do differ dramatically so shared environment only goes so far.

Interestingly, men and women in certain professions (shared environment) DO indeed have a skewed gender ratio - just to throw out a few from the Journal of Endocrinology (in other words, actual studies and not pulled out of my tush) - professional drivers, pilots, fungicide applicators, astronauts, and deep sea divers all had more daughters than would be statistically expected.

[nuthinbutpink]

Now - I DO NOT believe gender "runs in families"...exactly. I do not and will never believe for one minute that there is a "boy gene" or a "girl gene" that either man or woman carries (and I will write an essay about this to explain why in depth).

What I DO believe is that ALL people everywhere have some sort of mechanism that sizes up their environment and "decides" on the basis of that, whether a boy or a girl has a better shot at survival and successful growth to reproductive ages. Since families oftentimes share the same environment (or at the very least did during their formative years), it seems reasonable to conclude that some families will have indeed more of one gender than would be statistically expected based on this shared environment. But obviously, even in the same family, siblings' experiences can and do differ dramatically so shared environment only goes so far.

Interestingly, men and women in certain professions (shared environment) DO indeed have a skewed gender ratio - just to throw out a few from the Journal of Endocrinology (in other words, actual studies and not pulled out of my tush) - professional drivers, pilots, fungicide applicators, astronauts, and deep sea divers all had more daughters than would be statistically expected.

Occupation

When the sexes of the exposed parents are controlled, paternal exposures to a number of chemicals used in war and agriculture (herbicides, pesticides, fungicides, etc.) reportedly reduce the sex ratios of subsequently born children. In some such studies, men have been exposed to a cocktail of chemicals. In the ideal study, there should be data on the exact chemical agents, on the endocrine profiles of the exposed workers, and on the sexes of offspring of the exposed workers. However, as far as I know, such data are available in only one set of studies. Garry et al. (2002a,b) reported significant excesses of daughters born to the wives of fungicide applicators. These workers also described a significant negative correlation between the men’s testosterone concentrations and their number of daughters (Garry et al., 2003). These authors concluded that fungicides seem to determine the sex of offspring. I suggest that this is correct, and that they do so by lowering the testosterone levels of exposed men. In the following section, the sex ratios associated with exposure to some chemical compounds are treated individually.

Professional drivers have an excess of daughters due to poor sperm quality, and the evidence that lead lowers male testosterone levels.

Source:http://www.springerlink.com/content/k7l3476724p06215/


Professional diving
Rockert (1977) reported 20 sons and 40 daughters born to deep divers in the Swedish Navy. Lyster (1982) reported 45 sons and 85 daughters born to Australian abalone divers. This is thought to be due to lower levels of testosterone.

Pilots of high-performance aircraft and spacecraft
Low testosterone/gonadotrophin ratios in such men and in experimental animals have been reported by Ortiz et al. (2000), Strollo et al. (1998) and Strollo (1999) resulting in more daughters born.

[atomic sagebrush]

To toss in an anecdote to illustrate how complex the issue of shared environment can be, my good friend (has 3 sons) whose husband is a pilot in the military...virtually all the guys he works with have all daughters. They even ask my friend and her husband what they should do to "get a boy". Why, despite of the shared environment, are they the ones that have sons when all the other guys have daughters? Maybe he is just physically resilient to the effects of his environment, maybe his diet helps somehow, maybe it's just luck, maybe it's what she brings to the table.

In other words, NO ONE should give up hope and say, well, it's my environment, it can't be overcome...

[Lilian78]

Wow, I think I'm going to have to read both studies! And maybe get DH into diving LOL.