h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

it is almost exactly 50/50... half biologically female and half biologically male...
how can that be?

theres some usable data here:
http://en.m.wikipedia.org/wiki/World_population
especially under the Demographics heading

It's genetic - any 'natural' conception has a 50/50 chance of turning out male or female. It's only when you use IVF and so forth than you can skew the balance, although that's illegal in most (all?) countries at the moment (except under exceptional circumstances).

Cultural effects (such as the killing of female infants in cultures where boys are more valued) can skew things, but only very slightly on a global scale.

Gender in humans is determined by the male parent. Men's sex chromosomes are XY and women's are XX - all chromosomes are paired, but the chromosome that determines 'maleness' is a Y-shape rather than an X shape.

Your body makes a new set of chromosomes for every new cell. Most human cells contain 46 chromosomes; sex cells, however, only contain 23 (because the nuclei of the sperm and egg fuse to make a full complement of 46). Each sex cell takes exactly half of each of the 23 pairs. This means half of the male sperm cells contain the X chromosome and half contain the Y chromosome. All egg cells contain the X chromosome. This makes it a 50-50 chance whether a fertilised egg cell will develop into a boy (egg X + sperm Y) or girl (egg X + sperm Y).

I suspect, however, that wasn't the answer you were looking for.

B

"I suspect, however, that wasn't the answer you were looking for."

no... that's good, that's good.
a good data base

so, half of those sex cells (sperm) coming from the male have a y chromosome, and half have an x chromosome?

so x sperm and y sperm are different
so why do they have "equal" potential for success?
i don't think they do

the reason that i think the potental for success for any given sperm varies
is because each sperm is different from every other sperm

just having an equal number of each kind of participant does not guarantee that there will be an identical pattern of kinds amongst the winners

in a tournament, races between 50 rabbits and 50 tourists will not necessarilly result in an equal number of rabbits and an equal number of touristsmaking the finals

Why do you think X-sperm and Y-sperm are different, when the outcome (i.e. ratio of male to female) strongly suggests that they aren't?

The X or Y chromosome donated by the father determines the sex of the child - women only have female chromosomes.

There is not a 50/50 chance in each individual male. A man who has fathered 3 sons already has more of a 70/30 chance of fathering another son next. Opposite scenario if he has 3 daughters already. There are huge studies and debates about external influences (temperature, diet, date of conception etc) on the probability of either sex child.

But over a large population that more or less evens out. Some men will father more girls, some - more boys. When you have 2 options in a huge random subject base, probability says that close to 50/50 is the result.

The properties of sperm cells are not dictated by their individual genetic makeup. The DNA contained in every cell contains the full blueprints for an entire organism.

Far more important than the chemicals in their nucleus will be the cytoplasm, and indeed the concentration of mitochondria. These are the organelles that convert glucose to energy and will have the most impact on a sperm's swimming speed. The most impact that an X or Y chromosome will have is that Ys are slightly smaller and weigh less. But that's just silly, really.

B

dannyb, the 50/50 outcome of boy and girl babies may not necessarily be only because the income is also 50/50

for one thing, a male may MAKE a million x sperm and a
million y sperm in any given go... but will they all make it out of the gate, and if they do... in 50/50 order?
not to mention that having y in your cellness makes you Different from having x in your cellness

okay
you all are doing great here
im just gonna stand back here and learn

In a horse race with 30 million horses, about half of whom look grey and half look brown, would you take the trouble to count them if offered an even-money bet that a grey horse would win?

And, again, the genetic information is negligible with regards to the properties of an individual sperm. Your DNA describes a full living organism, not the specific cells in which it happens to be.

B

"And, again, the genetic information is negligible with regards to the properties of an individual sperm. Your DNA describes a full living organism, not the specific cells in which it happens to be."

so, are you saying that gender is, in the bigger picture at this point in time, for humans, not a significant factor in natural selection?

and, is it possible that in past times the world population could have been, say, 30 % females and 70% males?

pffft - everybody knows the Storks Union insists on a gender-balanced delivery rota, combined with Positive Action measures to promote Ethnic Minorities who have suffered historical prejudice accessing the cabbage patch.

sorry...

"so, are you saying that gender is, in the bigger picture at this point in time, for humans, not a significant factor in natural selection?" and therefore as statistically predictible as the outcome of coin tosses?

There seems to be some feedback mechanism. It is said after a war, more boys than girls tend to be born. This would help repopulate the male population, which would likely have lost a large percentage. Apparently it has to do with how male and female sperm don't have an equal life span, and so how often a man has sex will influence which one will prevail. An abundance of women will mean each man has sex more often, and the shorter lived male sperm will do well enough. This is all something I recall from reading an article years ago on the subject, it might not be true at all.

it is very interesting, Xanatic, and lotsa food for thought...

like this one
maybe it isn't so much about abundance if women
don't forget that rape is also a factor in war

maybe it isn't so much about abundance OF women...
don't forget that rape is also a factor in war



sorry

Rape should just lead to more babies, not more male babies. Besides, it's meant to happen *after* the war.

does anyone really know what percentage of babies conceived within the nine months prior to the end of an occupation is due to rape?

i mean, isnt that something a mother May want to conceal, if possible?

anyway, i'm just saying it might not be just because there are More women that men are having more frequent sex

> Men's sex chromosomes are XY and women's are XX.

This is, to put it mildly, a gross overgeneralisation. Sexuality is far far more complicated than that, and the above statement is inaccurate for a non-trivial number of people.

TRiG.

#1: "it is almost exactly 50/50... half biologically female and half biologically male...
how can that be?"


I think others have answered it but what were you expecting (e.g. 60/40?) and in what direction (more males or more females?).