Are some males more prone to producing one sex of baby over the other?

Factual Questions
1

This is a question that I have wondered about for some time. We all know that the male sperm is what determines the sex of his offspring. The ratio at conception runs roughly equal for male to female conceptions across the population (with a small bias towards higher male due to higher mortality at all stages of development).

What about for individual males? I see families with many children that have some pretty lopsided sex ratios all the time. I know enough about statistics to realize that even an unbiased coin will produce short runs of one result consistently.

I have one daughter now. If I decide to have four more kids and the next three are also girls, does that mean that the final one is more likely to be a girl than for most people? Again, I know the answer for a coin toss. This question is about a biological system and whether it is different.

2

I know a couple who have four sons. When the sons grew up and started families it was boy after boy, until there were eight male grandchildren and no sign of a female… until this year. They are all doctors and when the baby girl was born one of them complained that his plans for using his family as a case study for this hypothesis had just gone up in smoke. :wink:

3

I started a similar thread a while back here .

Some people basically said that it doesn’t matter - male sperm is 50/50 - but to be honest, I’m still sceptical, as I’ve seen multiple times where a family is so male dominated in terms of offspring that it just doesn’t seem to make sense.

4

Alternate hypo: It may not necessarily be because they are making more Y than X sperm (or viceversa), but it could be that some other X-linked or Y-linked trait makes one or the other sperm more viable, or more mobile, or likelier to fertilize, or the resulting zygote more or less likely to survive early stages or to implant.

5

A book I read recently, Adam’s Curse, said that there was evidence for an inherited predisposition to male offspring in some families, but I was not completely convinced. Much of the book seemed a little too uncritical of the evidence for interesting ideas like this. (Which is a bit of a shame, because I think it’s a fascinating subject).

And four children of one sex would not be that uncommon even if sex was completely 50/50 random. Or even 12 male offspring (as the two generations in Martha’s example). There’s a one in four thousand chance of that (make it two in four thousand to get all males or all females). This sounds kind of small, but if you randomly divided the U.S. population into groups of 12, you’d have between 1 and 2 hundred thousand same-sex groups.

Which is not to say that there aren’t nonrandom factors influencing a child’s sex. There are (consistently and in a statistically valid way) more males born than females, so clearly it’s not completely random.

6

The formation of male gametes begins with a cell that is, genetically speaking at least, perfectly normal for the male’s body. It has one X chromosome, one Y chromosome, and the 44 other chromosomes arranged in 22 pairs. When meiosis begins the pairs of chromosomes line up at the cell’s “equator” and then each pairs divides so that each daughter cell gets one chromosome from each pair. But everything (i.e. every protein) is a daughter cell’s cytoplasm was made from the DNA of the original cell with the full set of 46 chromosomes before the split, so the two daughter cells are identical except for their DNA.

7

I’m not an expert but I have read about planning for a boy or girl that’s about 80% effective. The book (Taking Control of your Fertility) explains that “male” sperm and “female” sperm are different. Female sperm tend to be hardy sperm but slower while male sperm is faster but don’t last as long.

So if this is correct I can’t see why genetically a guy can’t have fast AND hardy male sperm. It would greatly reduce the chance of female sperm making it.

8

One theory I’ve seen put forth is that it isn’t the father, it’s the mother; according to this theory, “boy” sperm do better in an alkaline environment, and “girl” sperm do better in an acidic environment; therefore, if the mother is more alkaline, the tendency is to produce boys (my MIL had five sons and only one daughter); if the mother is more acidic, the tendency is to produce girls (my mother had five girls, no boys; I have three girls, no boys). This theory was put forth in a book I read about gender selection before getting pregnant with my last child. It entailed (put in spoiler box because it may be TMI):

Douching with baking soda and water, and me not having an orgasm.

9

I guess I should have read through before posting my question.

How much more likely are you to have a boy if you have an orgasm?

10

According to the book I read (can’t for the life of me remember the title), I was more likely to get a boy if I didn’t have an orgasm. I wasn’t even supposed to get very turned on. Needless to say, this lead to some very unsatisfying sex, and after all that, we still got another girl!

11

It’s well known in domestic animals, such as horses or cattle. You will even see advertisements for stud services that say things like “produces 85% female offspring”. And with pedigreed animals, this is accurate – it can be easily checked.

If it happens in other mammals, I don’t see why it couldn’t happen in humans.

12

It seems the sperm is only partially responsible for the gender of the offspriing. That is, chromosomally it determines gender, but a myriad of variables affects which sperm will fertilize the egg.

There’s actually quite a bias in favor of male conception, for reasons which are largely unknown. 62.5% of conceptions are male, and 53% of live births are male. This may have to do with faster male sperm and people who are trying to conceive having intercourse right near ovulation. (We talked about this a little bit near the end of this thread.) It may have to do with barrier methods that are fail near ovulation due to the mechanical and chemical changes within the woman’s reproductive tract. It may be some more scientific explanation of: nature “knows” males are more fragile and likely to die in utero or as infants and so has made provisions to skew conception toward males. It’s also likely that the excellent prenatal care and nutrition so many women recieve nowadays is saving baby boys that 100 years ago would have miscarried. The old 50:50 model, while still taught in high school biology, is patently false when investigated more closely.

There are plenty of theories that the diet of the man is just as important as the diet of the woman in gender selection. Most of them are of questionable scientific validity, though anecdotal support can be substantial.

While I can’t find a cite, there are apparently studies showing that men who work with toxic chemicals more often father girls. One study in particular was done looking at offspring of male anesthesiologists and showed a notable bias towards girls. (It’s mentioned in Taking Charge of Your Fertility, but not cited.)

Also, here’s an agonizingly long article here detailing the scientific research behind the oft-noted factiod that poor women tend to have more girls and wealthier women more boys. Although many people see this as due to nutrition, prenatal care and stress (again, with baby boys being more fragile and not surviving a tougher pregnancy as often), these authors have found evidence that even *conception * of females is oddly higher in lower income women. “…research has shown that a more resource-rich prospective environment translates to a son bias, whereas a lack of such prospective environment translates to a daughter bias (Mackey, 1993; Mackey & Coney, 1987; Mealey & Mackey, 1990; Teitelbaum, 1970; Teitelbaum & Mantel, 197 1; cf, Gangestad & Simpson, 1990; Grant, 1994; see Chahnazarian, 1988 for a review of the literature). See Grant (1994), Gualtieri, Hicks, & Mayo (1984), Guerrero (1975), Harlap (1979), and James (1986, 1987, 1992) for candidates for proximate mechanisms (e.g., hormone levels and psychological types) that bias the human sex ratio, generally at the level of conception (the primary sex ratio).”

13

My understanding is that whatever the gender of your first child, it is ever so slightly more likely that any subsequent children will be that gender. Sorry, no cite.

14

I remember a study that came out a few years ago stating that the first child was more likely to be the same gender as the older partner in the couple. If Dad was older than Mom, then the first baby was more likely a boy. The greater the age difference, the more disposed towards one gender over the other.

15

That’s interesting but it’s certainly not the way I’ve seen things work. Hubby’s older than me, and we have all girls. My dad was older than my mom: all girls; my MIL is older than my FIL, 5 boys, one girl.