Do men produce xx & xy sperm in equal numbers? And do they have the same motility? I guess my question ultimately is does every conception have an equal chance of being male or female?
http://users2.ev1.net/~blakely52/Dna/DNA%20project.htm
Think about it–if male homo sapiens really did produce, say, more “male” sperm than “female”, then, statistically speaking, worldwide we’d have many, many more boy babies than girl babies being born.
Which is not the case.
Well - there ARE more boys than girls born worldwide. But I meant to ask if there were individual differences and if sperm viability or motility differ according to which chromosomes they carry.
I’m talking about “vastly more boys than girls born worldwide, for the human race, overall”.
http://geography.about.com/library/faq/blqzmalefemaleratio.htm
The boy/girl ratio is also given as 52% in many places. Statistically speaking, 52% or 105 boys to 100 girls is not a huge difference. It still pretty much amounts to a 1:1 ratio.
There does appear to be some difference in motility and viability:
I disagree. I think 105:100 over such an enormous sample size is a huge discrepency, and certainly invites questions…
Also, just because the sex ratio is about 50:50 does not necessarily bring the conclusion that X and Y sperm are created in the same numbers. There are different factors (mobility, viablitly, as has been mentioned) that can skew the results.
Upon preview, I see Darwin’s got an interesting citation.
Actually, a gender imbalance can be unfortunately explained by female infanticide and the termination of female fetuses (fetii?). If 3 out of 50 female fetuses were aborted in India and China alone (the rates are probably much higher), it would be enough to make a significant statistical blip worldwide, since these two nations comprise close to one-third of the human population.
India and China have considerable cultural biases against female infants and this must be taken into account in any discussion of human gender imbalance.
That’s a very good point, Bryan. I guess we’d have to examine the data from countries where female infanticide is not common. However, wouldn’t most of these deaths occur post-birth? I suppose we also have to consider how the recordkeeping is for females who are killed after the fact. I suppose the birth wouldn’t be registered and would account for the statistical discrepency.
However, Darwin’s article seems to make a very extreme point which would not take sex-based abortions or infanticide into account.
According to the CIA World Factbook, here are some birth ratios:
USA - at birth, 105 males:100 females; at 0-15 years, 105:100
Canada - 105 males:100 females; at 0-15 years, 105:100
India - 105 males:100 females; at 0-15 years, 106:100
China - 109 males: 100 females; at 0-15 yers, 111:100
Hong Kong - 107 males:100 females; at 0-15 years, 113:100
Norway - 107 males:100 females; at 0-15 years, 106:100
Sweden - 106 males: 100 females; at 0-15 years, 105:100
Finland - 103 males: 100 females; at 0-15 years, 104:100
WORLD - 105 males: 100 females; at 0-15 years, 105:100
There’s still plenty of discrepency that can’t be put down to infanticide.
>> a gender imbalance can be unfortunately explained by female infanticide and the termination of female fetuses (fetii?). If 3 out of 50 female fetuses were aborted in India and China alone (the rates are probably much higher),
Bryan Ekers this is total crap as pulykamell’s statistics show. Your first link lists some sources and starts by saying “some of these sources are very opinionated”. A better word would be “lying” for their own ends.
Female infanticide is rare in China and there is no way in the world it would approximate the 5% needed to balance things. Not to mention that then, we have to conclude from the statistics that female infanticide is just as common in western nations. Anyone care to defend that as a fact?
Sailor- true, but it’s still pretty interesting.
India is often cited as being the worst offender in terms of infanticide, yet the male:female birth ratio is the same as the world average.
However, China’s stats are a bit skewed.
Going by the numbers:
2001 est. population: 1,273,111,290
Births per 1000: 15.95
That should mean about 798,189 births for these 2001 stats.
Of these we should expect (by world averages:)
Male: 408829
Female:389360
Instead, we get:
Male:416280
Female:381909
Or 7451 more male births than expected. Is this statistically significant? Somebody with a better statistical background than me would have to run one of them funky chi-square tests or whatever it is. It seems to me that with such a large population size, this MAY be statistically significant. At least its curious to see that no other countries I can find report such wide deviations.
Would infanticide be to blame? Of course not necessarily. Underreporting of female births or discrepencies in census taking are more immediately likely culprits.
I heard this from a friend (who read a bunch o’ baby books): She said that the “boy” sperm are faster and the “girl” slower, but boy sperm dies more quickly and girl sperm lasts longer. Soo…if you want a boy, have intercourse when you ovulate, but if you want a girl, have intercourse a few days before you ovulate.
But I guess that has nothing to do with the original OP’s equal number question. Just thought it was interesting. Sorry, I have no site. Just a friend telling me. She sounded very authoritative, however.
Er…“cite”, rather
The fact is male sperm run faster and can lift more weight and do more pushups. When I was just a sperm I outran several female sperms to the egg, so there.
Oh, you wanted a factual answer? Darwin’s Finch already provided it.
Well, here’s statistically what I’ve been able to come up with. Those more fluent in stats, please check my work. It’s been years since I’ve done this.
Assuming a normal binomial distribution, with a p=0.5 for male births.
According to the worldfactbook, there were 6,157,400,560 people on this earth in 2001 and 21.37 births per thousand. That equals something like 131,573,649 births.
Assuming a normal probability distribution, we should expect a mean of 65,786,824.5 male births. The standard deviation is 5735 for this event.
Our actual numbers show 67,391,381 male births. According to my z-test, this is well outside the range of simple chance, with the probability of this occuring less that .01% by chance. (This figure being 279.77 standard deviations away from the norm.)
It seems clear to me that p(Male at Birth) is not .50, but rather .512195.
Extrapolating these results on the Chinese case, our data is +16.69 standard deviations away from the norm. Also, less than .01% by chance.
Statisticians, please critique this work, but it seems OK to me.
I don’t think anyone has directly answered violet9’s first question yet, namely “Do men produce xx & xy sperm in equal numbers.” The short answer is yes. (Of course, sperm aren’t typically xx or xy; they’re x or y, but we know what you meant.)
Standard males are XY. When a sperm is created, diploid cells undergo meiosis, taking one chromosome from each pair. This means that half the resultant cells will have an X, half will have a Y. Now, the rest of this thread has discussed viability and motility advantages that suggest why more babies are XY than XX, but at this early stage, numbers of sperm will be equal, because from each parent cell, two sperm are created, one X and one Y.
–Cliffy
Did you forget to take your lithium? Infanticide is only part of the imbalance. The abortion of female fetuses is a common practice in India and China. Although ultrasound machines are officially meant to determine the health of a fetus, they are used more commonly to determine its gender. Indian and Chinese women don’t have to give birth to a daughter, and then kill her. The means exist to determine the child’s gender well in advance of birth and if the pregnancy is terminated, it simply doesn’t appear anywhere in birth statistics.
Excuse me while I call BULLSHIT on you, though infanticide rates may drop simply because commonplace ultrasound exams and increased female fetus abortion may make infanticide less necessary.
As inexpensive ultrasound machines penetrate further into rural areas of China and India, the gender imbalance will get worse. A five-percent difference in Western nations may be the result of sperm motility or any number of factors. When the Chinese and Indian gender difference slide beyond the ten-percent range, female fetus abortions (and infanticide) become the most obvious factor. And since China and India are about one-third of humanity, a major statistical blip to them becomes a noticable blip to the rest of us.
is it possible, then (atleast in theory), to extract either XX or XY type from a given sample of sperm ?
unless i’ve misunderstood the concept totally
Yes, xash. It’s called spinning.
Let’s say you want a girl. Well, little girl sperm are heavier than boy. So they put your sample in a machine, spin it round and round and round, and it separates the boys from the girls. Take the clump of girl stuff, insert it, and hopefully you’ve got yourself a girl.
Vice versa if you’re wanting a boy.
I’ve always wondered if certain women did not put out eggs that “rejected” certain types of sperm. There’s gotta be an explanation for these families that go like, 5 generations and only have boys (or girls).
The men in my family can’t pop out a boy to save their lives.