Why is the male/female ratio constant?

[Byanca]

How does nature achieve this. The numbers are about the same from each. It doesn't matter of one fornicates in equator or the north pole. Black or white or in-between. Stupid or smart. No. The balance stays the same.

How on earth does this stupid planet know, or even decide on roughly 50/50(males a bit on the + side). I presume the phenomena is the same with other species.

[sandra-leigh]

It doesn't. The ratios vary with location, diet, and genetics. The sexual determination mechanisms are very different for some of the other species (e.g., based upon the temperature the eggs are incubated at.)

[seanmuscle]

Because there are equal number of Y and X sperm. So always 0.5 chance. They say a male with prenatal exposure to estrogen and progesterone in the womb can develop feminine characteristics, ie: love to wear womens clothes, more gentle, more social etc...

[Byanca]

How much variation? Disparities are caused by other factors. But the natural ratio of female newborns to male newborns around the world is always approximately 50/50 at birth. And for all the sexual species the ratio is 1:1.
http://en.wikipedia.org/wiki/Human_sex_ratio

But that article is mostly blabla bla. Does not answer the why. Or how the egg and cell knows what it should be this time.

What creates the balance?

Edit. Why is there equal number of x and y sperm? What determines the sperm count?

[Simply_Vanessa]

Law of Averages. Boys have a shorter lifespan though, so there are statistically more women in most of the world.

[Amelia]

I'm sure there is some overly complex explanation, but perhaps we should leave it at magic.

[Cynthia Anne]

What ever the reason is I don't care! I would rather work on the ratio of cds to non cds!

[KrystalA]

Whatever gave you the idea that the ratio is 50/50?

[Sophie86]

There is a theory that male sperm swim faster than female sperm, but die more quickly. Whether the egg will be fertilized by a male or female sperm, then, depends on how far down the fallopian tube it is when sex occurs. If it's close to the uterus, then the male sperm get there first. If it's father up the tube, then the male sperm die before they get there, and the female sperm do the fertilization. All one has to do in order to determine the sex of the child, then, is know when ovulation occurs, and time sexual intercourse accordingly.

This has worked in at least three cases that I know of. A friend of mine introduced me to it. He and his wife used it to produce a girl. My wife and I used it to produce a son. He knows of one other couple that used it successfully. In all three cases, the desire was to even out the male/female ratio in the family.

What this suggests regarding the male/female ratio is that, given an equal number of male and female sperm cells, and a random distribution for sexual activity, the ratio will be roughly even. It is, in fact, 105:100, rather than 100:100, but close enough.

[GaleWarning]

It is true that more males are born than females. However, males tend to die more often than females.
Have a look at the various population pyramids that one can find, usually in books dealing with geography or social studies.

[seanmuscle]

equal because males have X and Y chromosome. When a cell undergoes meiosis it can get either the X or Y chromosome. That is why there are equal numbers of X and Y mature sperm. We have X and Y chromosomes because it allows for sexual reproduction to occur which was probably an evolutionary advantage for our ancestors. If we go way back our first ancestor reproduced asexually.

[Byanca]

Whatever gave you the idea that the ratio is 50/50?


It is, in fact, 105:100, rather than 100:100, but close enough.


It is true that more males are born than females.

I beleave it's 1:1. Or a 100:100 at birth. I doubt they classify TG's properly.

[LeannL]

Sophie,
I believe I have a problem with the theory you state. I don't discount your experiences but the sample size is too small to validate. The problem I have is that, based upon your theory, assuming couples attempting to get pregnant are doing so frequently, then females should dominate because you can only get pregnant once per month and the first one wins. Also, when my wife and I were practicing Natural Family Planning, a study came out that indicated that sperm can survive in the women for up to seven days. (It sure made NFP a bit shakier after that!). So it may not be a sprint to the finish after all.

There is a evidence that the pH of the woman's organs and the sperm does affect the mortality of one gender producing sperm over the other. I am a chemist and there is seems to be a trend toward chemists producing more female offspring than male. The explanation being that chemists inhale more organic bases than they do acids. (With improving chemical hygiene, this bias should go away.) Thus, chemists may be at a slightly higher pH than normal especially if they excrete it through the sperm delivery tube. Again, this is a theory. No one has done the definitive double-blind study. Now what could this mean toward your observation? It could be that the woman's pH is dependent upon her progress through her cycle. To me, this would make more sense than a distance argument.

Leann

BTW, I have two lovely daughters and no sons.

[VeronicaMoonlit]

Easy, sperm (and eggs) are haploid, not diploid.

Usually, women have XX chromosomes
Usually, men have XY chromosomes.

The following is a vast simplification the cell that makes the sperm makes two, one with an X one with a Y. The cell in women that makes eggs makes two eggs, both with X.

When the males X hits that females X you get a female fertilized egg. When the males Y hits that fertilized X, you get a fertilized male egg.

And since half the males sperm is X and half is Y that's why you get the (near) 50/50. but it isn't exactly 50/50, it varies due to reasons pointed out above.

Didn't you learn this in school? It's covered in basic sex eduation or science classes at the junior high level.

Veronica

[Kaz]

Statistical variation I am afraid... boring as hell, but it should be taught at an early age... we would all be better people for understanding this very basic concept...