Why are males and females 50%-50%?

[cthulu2016]

Last edited Sat Feb 18, 2012, 03:57 PM - Edit history (1)

Edit: I enjoy learning things from posting threads and considering replies. In this case, I'll update/clarify the OP on a couple of things. Some of the specific statement in the OP are quite flawed, and others true in their implication but so sloppy as to be misleading. First, all humans start out as female and the males must then make a very tricky developental switch that is often fatal. So we adjust (tending toward the 1:1 sex ratio) by producing many more XY (male) potential persons than XX (female). But since many of the males fail by birth the ratio is about 105:100 male. The birth defect rate of males is higher and I would bet total pre-pubescent mortality is higher for males, again trending toward the evolutionarily stable 1:1 ratio. An environment can favor one or the other and that will manifest itself, but all things being equal the logic of sexual reproduction provides constant pressure toward 1:1, even if in the face of an environment that says otherwise. Googling Fisher's law offers the original theortical model of hy we tend toward 1:1 and Dawkins THE ANCESTOR'S TALE has a lovely chapter on Fisher's Law.

The overall point, though, is that neither male or female human beings are more "valuable" in evolutionary terms, and that whatever perception to the contrary is an artifact of culture, not nature. (It's pro-woman argument -- an approach like China that artificially favors males will run into natural head-winds because eventually those with sons will become less and less likely to have grand-children.)

Oddly enough, there's a concept missing I would expect. Primary sex ratio is at conception. Secondary is at birth. Tertiary is ratio in the whole population. But since the real import of sex ration is reproductive I would expect tertiary sex ratio to be breeding age population, and that's the one that ought to matter most because breeding, and only breeding, can perpetuate change or stability in sex ratio. I do not know this, but it's a good guess... Our primary is 170:100. Our secondary is 105:100. And our tertiary is female-heavy because women live longer. At some point the ratio is 1:1 and I would guess that crossover occurs during prime mate-selection age, because that's the goal. If tigers just loved little boys to eat and didn't care for girls then w would produce more and more little boys to keep the breeding population at rough parity.
________________________

We humans tend to think that having sons is more valuable and it may be in practice, but only due to artificial peculiarities of our economics.

Nature sees no difference in value, and it's interesting to see why. We create fetuses at a rate of 50% male, 50% female. That's our natural rate. And from that we know that in the evolutionary long haul there has been no advantage in having children of one sex or the other. (Meaning that any perceived advantage is social/cultural.)

The genetic math of males (at least among mammals) is that sons are high-stakes gambles and daughters are "sure things." A son might sire a thousand grandchildren but will often sire none. A daughter is fairly sure to give birth to as many off-spring as her body can handle, which is a smaller number.

An individual creature can easily have the trait of producing only males or only females and if there was any evolutionary advantage (meaning a higher number of grand children, great-grand children, etc.) then there would be a lot more males or females born, accordingly.

In a population of 90% females there will be almost no monogamy. Any son is likely to produce scads of grandchildren. Harems would be the norm. The value of sons (in genetic survival terms) would be sky high and anyone who produced more sons naturally would find their genetic material spreading through the population. Those likelier to produce daughters find their genes squeezed out. More and more males are born.

In a population of 90% males the average male will produce no off-spring. The average male will be killed in competition with other males, or driven from sociaty as a rogue male. The situation would be so extreme that cultures would start summarily "exposing" most male infants. The value of producing daughters would be immense, and anyone with a knack for producing daughters would find their genes spreading and more daughters would be born.

And in species after species the stable distribution is 50-50%. Any temporary swing one way or another is smoothed out naturally and other traits change to support the 50-50%. For instance, if females cannot collect enough food during pregnancy or early child-rearing then other traits rise in value, like monogamous families or cooperative tribal organizations.

In human society, however, we can create laws or customs that favor males economically and create situations where parents opt for sons, and we often have. But they are genetically unsustainable and even economically unsustainable in the long run. If China had 70% male children then the economy must change. Reverse dowries would develop where a man could only gain a wife by securing the financial security of her parents... the reason (security) people opt for sons would develop into a reason to have daughters. Women would become more valauble, in every way. And such a China would probably find itself moved by the invisible hand of population dynamics to find reasons for wars, decreasing the male population.

The system can be gamed for a genration or two so people will do so, but in a world where all parents chose the sex of all children we would soon settle on parents in aggregate choosing 50-50% as the social and economic value of the sexes changed to accomodate the practical numbers.

Here's a very cool side note: Humans relibaly produce a tiny number more females... 50.1% to 49.9%, something like that. One theory of the discrepency is that mitacondrial DNA may find a subtle way to try to favor spontaneous abortion of males because mitachondrial DND comes entirely from the mother and can only be passed along by daughters. I am not suggesting that is the reason, it's just a beautiful theory.

[Brother Buzz]

1. Silly me, I learned the natural ratio at birth was 107 boys to 100 girls

[cthulu2016]

2. That's birth, not conception.

Our species naturally creates fetuses at almost exactly 50-50 with a tiny, tiny edge for females.

What we do after conception is different.

In anthropology and demography, the human sex ratio is the sex ratio for Homo sapiens (i.e., the ratio of males to females in a population). Like most sexual species, the sex ratio is approximately 1:1. In humans the secondary sex ratio (i.e., at birth) is commonly assumed to be 105 boys to 100 girls, an assumption that is a subject of debate in the scientific community. The sex ratio for the entire world population is 101 males to 100 females

http://en.wikipedia.org/wiki/Human_sex_ratio

[muriel_volestrangler]

8. Primary sex ratio up to 170 males to 100 females

The primary sex ratio (male:female ratio at the time of fertilization) in humans differs remarkably from the theoretically expected ratio of 1:1, and may be as high as 170 males to 100 females (Pergament et al., 2002). Because the secondary sex ratio (or ratio at birth) is ∼106:100 in the majority of developed countries, it is clear that preimplantation and prenatal mortality affects sexes differently.

http://humrep.oxfordjournals.org/content/20/9/2662.full

(On edit: added 'up to')

[cthulu2016]

12. Fair enough

I should not have said conception. Particularly since all fetuses are developmentally female and must make a tricky change to become male, which results in a high failure rate. (And accounts for the greater variability in males born, also. Higher defect rate, etc.)

But by noting that discrepency in what I said your are arguing my case (which isn't my case, of course, it's everyone's case).

The huge spontaneous abortion rates of male mini-fetuses mandates an over-production to acheive rough parity in actual, practical reproductive terms.

Either way, our species (and a lot of others) will graviate toward a practical 50-50 for very good reasons.

[Honeycombe8]

19. I've read that there are more males than females are born in the U.S.

So why were there fewer males than females in my generation? I'm in my 50s. Because the guys died from war and from doing what you might call risky things, like driving 100mph while drinking, or mountain climbing, or speed racing, or running four wheelers fast over hilly terrain.

[cthulu2016]

23. I ammended the OP to reflect

that the sex-ratio that matters is the ratio in the breeding age population, not at conception or birth. And any mechanism that causes younger men to die more than younger women will require a starting-point surplus of males to be near 1:1 when it matters.

[Arugula Latte]

7. Also, boys traditionally had a higher mortality rate.

So by a certain age, the population is 50 - 50.

Then, of course, in later life, women outnumber men significantly.

[karynnj]

3. Speak for yourself

I certainly do not think that having boys is more "valuable" than girls - both my husband and I were and are extremely happy and proud to be the parents of 3 daughters.

[FarCenter]

4. The ratio of boys to girls at birth ranges from 1.03 to 1.07 generally, depending on country

http://en.wikipedia.org/wiki/List_of_countries_by_sex_ratio

So there are slightly more boys than girls born. However, the ratio for people over 65 generally is considerably less than one, reflecting the shorter life spans of men.

The reason for rough equality in humans is that the male germ cells have a Y chromosome and an X chromosome. The cell divides by the process of meiosis to produce two haploid gametes: one sperm cell with the Y chromosome and one sperm cell with the X chromosome.

PS -- Nature has a variety of ways of doing things. Bees, for example, produce very few queens (female), more drones (males) and lots of workers.

[HereSince1628]

5. Sex ratio is a feature of a species natural history traits

within population biology, NH traits are those that show up in life-tables.

Life-tables reflect survival and reproduction--the traits that define "Fitness"

Consequently, natural history traits are considered to reflect combinations of a species traits which influence fitness and thus reflect some measure of resolution to the pressure of natural selection.


If you actually look at human sex-ratios, you'll see that it is a phenomenon that varies by age and history. History itself of course representing myriad and complexly interacting cultural variables in life contexts that show up as variations in life-tables.

When you look at an example of sex-ratio by age over history, you'll notice that the notion of 50-50 isn't precisely true even at birth, and at different times in history the ratio has significantly departed from 50-50 at different age.


http://www.infoplease.com/ipa/A0110384.html

[gulliver]

6. Maybe it maximizes the experiment potential.

Sex is all about life dealing with the prevailing environment. The selection for procreation success is determined by the environment. It would be hard for the environment to communicate ratio preferences to the reproductive system. The sorting is done the hard way after birth.

[retread]

9. Assume there is such a thing as truly random, then random coin flips are 50% heads 50% tails.

[HopeHoops]

10. By population, women in the US make up about 52%, partially by attrition.

Men tend to do more stupid stuff and die earlier.

Disclaimer: I'm a man and I've done WAY too much stupid stuff.

[napoleon_in_rags]

11. I think the ratio is about bottlenecks

the 50/50 distribution simply maximizes the chance of having a breeding pair if the population is dramatically reduced down to a few in an area. Remember, for hundreds of thousands of years people were almost an endangered species. Probably like that with any species.

edit: Its really interesting to think about Harem world. Given the limited sexual dimorphism of humans, which kind of genes would make it? The big tough person or the little cute person? It seems to me, that with 90% of offspring being female, those who would pass on their genes would be those with the genes that make the females most sexy, (because they are most likely to manifest) and these would be passed on to the males as well, so everybody would be elegant and cute, males too. The only way to avoid this would be if sexual dimorphism increased.

[cthulu2016]

13. That's attractive but cannot be right

Evolution doesn't plan. We could say "All the species are 50-50 so it appears that only 50-50 species have survived so perhaps only 50-50 species were likely to make it through bottlenecks" but that would only be right if the sex ratio were almost impossible to change. (Which we know it isn't.)

The moment an advantage appeared it would manifest itself. So we would be looking at a world where cats have 90% female kittens or people have 70% males or whatever was most favorable outside the eventuality of a bottleneck.

And we would say, "Cats will be in trouble if their population is reduced to five cats because theres a decent chance they'll all be female."

But if it works in the current environment that's what will happen in the current environment. Always.

[napoleon_in_rags]

15. Hmm, interesting.

"but that would only be right if the sex ratio were almost impossible to change. (Which we know it isn't.) "

I do think that is a bit of an oversimplification. To me the question is, what is the probability of change? CAN it change dramatically and quickly? If it can, there should currently be people who have more girls genetically and people who have more boys genetically.. Let see if its true...
Yep!
http://www.sciencedaily.com/releases/2008/12/081211121835.htm
(I had no freaking idea.)

So yeah, that supports what you're saying. Fascinating.

[napoleon_in_rags]

17. No here is the answer, Fisher's principle.

http://en.wikipedia.org/wiki/Fisher%27s_principle

1) Suppose male births are less common than female.
2) A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring.
3) Therefore parents genetically disposed to produce males tend to have more than average numbers of grandchildren born to them.
4) Therefore the genes for male-producing tendencies spread, and male births become more common.
5) As the 1:1 sex ratio is approached, the advantage associated with producing males dies away.
6) The same reasoning holds if females are substituted for males through-out. Therefore 1:1 is the equilibrium ratio.

No bottlenecks, no magic, just a simple formula. Its interesting to look at this playing out economically as well, as your OP says. The fascinating thing is to watch these forces drive culture, like in China where the dislike of female children will clearly become less and socially acceptable as these forces kick in with the male population.

[cthulu2016]

18. Exactly (I was trying to say that in the OP but may have failed)

An advantage on either side is exploited until it becomes a disadvantage, oscillating around a stable point.

So these Chinese folks opting for boys may benefit due to the inertia of existing culture, but it cannot last.

Parents chose a boy because the boy can contribute to their security in retirement. I predict that as women become scarce they will become a valuable commodity and parents will charge potential suitors the same money for their daughter's hand they would have gotten from a son. A reverse dowary.

No matter what happens, as long as women want husbands and men want wives there's only so much room for discrepency before the society shifts.

I am fascinated by the social mores of Australia that persist from it's early days of a society with very few women. Or the social mores of post WWI Europe where there was a big shortage of men. Our societies are calibrated to roughly 50-50 and any substansial deviation from that breaks down sexual custom quite quickly, since our sexual customs are both derived from and supportive of that expected mix.

[FarCenter]

20. It's probably more complex than that, particularly in species which are polygynous and bear litters

Environmental factors also play a role. See for example "Striking variation in the sex ratio of pups born to mice according to whether maternal diet is high in fat or carbohydrate"
http://www.pnas.org/content/100/8/4628.long

In humans, one might expect similar phenomenon in hunter-gatherer societies that suffer high rates of violent death defending hunting grounds, or in societies that practice polygyny.

[cthulu2016]

24. Very true

I really made a hash of the OP by stating the end point as the starting point. All species seem to have strategies for varying sex ratio somewhat in response to environment, but the effective ratio -- the breeding population ratio -- will tend toward 1:1.

A remarkable example of the sort of thing you're talking about is that monkeys change the sex ratio dramatically based on the size of the troop -- smaller troops can less afford to gamble on high-risk/high-reward males.

I stand corrected. Repeatedly!

[napoleon_in_rags]

30. Yeah, you're right... Here's a good article:

http://well.blogs.nytimes.com/2008/04/23/boy-or-girl-the-answer-may-depend-on-moms-eating-habits/

This article doesn't zoom in on meat/fat in particular, but rather calorie intake.

In animals, more sons are produced when a mother ranks high in the group or has plentiful food resources.

So maybe a male with higher social status (assuming its likely to be passed on) has better chance to spread genes far and wide than a female with high social status? I guess I can see it in humans: Mr. Rockstar sleeps with all the chicks who come backstage, but miss movie star doesn't want to hook up with every lowly guy she meets.

[cthulu2016]

34. Again, note the "afford to gamble" factor

Just like with monkeys, where females in large groups produce more males.

Well fed and high ranking females have a better chance of having several children survive and can thus afford to "speculate" with more males, less likely to have children individually but each having the potential to be a Don Juan that will spread mom's genes far and wide.

If, however, you may only have one child survive you want that child to be female because is the safest method to ensure that your gene line doesn't end with you.

[napoleon_in_rags]

37. Yes indeed. Do you ever see this stuff holistically cthulu?

I mean, see how these genetic imperatives shape our behavior? Its a vision of both beauty and terror, I am wondering if you personally have had that experience.

edit: Great thread BTW, I have learned more about us humans looking up stuff on the net regarding this than I have in a long time.

[cthulu2016]

39. Me to. My approach to posting is atypical

I like to throw things out and see what comes back. I knew that our mix in the breeding population cannot stray far from 50-50, and I knew that males have a tricky fetal pathway and a higher defect rate, but if I hadn't posted this I wouldn't have learned (from researching replies) that the male sperm cells have a big advantage and that we get to 50-50 in breeding age only by creating so many more males in anticipation n of so many males dying along the way. (Mostly in utero.)

I do think evolutionarily most of the time and often with surprisingly "normal" results... it's almost comical how our strongest cultural ideas happen to be supported by the math of genes with no minds whatsoever.

For instance, abortion in cases of rape. There's the victims's rights angle (a woman shouldn't have to bear a child conceived by rape... it's the ultimate non-choice) and the holy-life angle (it isn't the baby's fault so why kill him/her?)

And then there is the evolutionary angle. If women carry rape-conceived babies to term then rape is a winning evolutionary strategy. (Which it is, or it wouldn't be such a human theme, particularly in the context of war.) And I support winnowing rape from the human evolutionary tool-kit.

The evoluionary angle is not decisive, of course. I'm not a eugenicist. But it helps explain why so many people draw the line there, even though few would be so impolitic as saying "If the baby is born the rapist won." But on some level we know that.

[napoleon_in_rags]

40. You bring tough questions to the surface.

Paradoxically, I like the professed Republican idea of property rights. Would you let a bum set up camp in your back yard? Would you let a bum set up a baby in your wife's uterus by raping her, and not aborting it? Is that okay? Is your wife's uterus a homesteading area? If your answer to the former is NO and the answer to the latter is YES, than you are a nutcase in my book, a pro-life Republican. The holy mystery of birth in my eyes is that a child comes from the love of a man which a woman consents to be born, there is order and holiness to it that bum rape does not approach. This is an orderly and beautiful universe, I don't believe in a God who flushes hundreds of thousands of living souls down the toilet every year through miscarriages. The soul enters only once its a done deal. I believe in a God of life and death who knows and does not fear the will of the woman who is to be involved.

I believe that our highest and most moral impulses will lead us in the right direction, political correctness be damned. Future planning in all its forms be damned, lets be true to ourselves and our own conceptions of the highest and see what happens.

[lumberjack_jeff]

28. well said. n/t

[quaker bill]

31. It is not a gene

it is a whole chromosome. Except for the rare trisomy, male / female is an on-off switch. If you get daddy's X you are a girl, if you get his Y you are a boy.

It is different with alligators, if the egg is incubated relatively warm, males are produced, relatively cool, females. Same genetic composition, males or females depends entirely on the temperature of the nest.

[napoleon_in_rags]

38. That process is not as random as it would seem though.

Check out post #20 and down, scientific research is telling us there is a lot more to it: You can shape the gender of your child while pregnant by your diet, for instance. This is a very exciting thread as far as learning, I tell you. I knew none of this.

[quaker bill]

42. Unless you are a mouse, no you can't.

At the moment of conception, you have either an X and Y, or two X chromosomes. Nothing about human maternal diet can change this. Biology is full of fascinating examples of different mechanisms for sexual differentiation. Virtually all brown common geckos are female, and are in fact the same gecko. This species reproduces by parthenogenesis. In short the eggs are fertile when made, and each gecko is a perfect clone of its mother.

There are a number of reef fish that will transgender. If there happen to be too few males or females in the local population, some individuals will literally grow the alternate set of sexual organs and switch gender. Humans don't do any of this naturally.

One does not become better informed by learning myth.

[HereSince1628]

22. It seems unlikely to me that a bottle-neck would lead to a change in species mating-systems

Bottle-necks result in reductions of genetic variability. Mating systems within a species are highly conserved and there probably isn't enough genetic variability in the controlling factors for mating systems to result in a shift when genetic variability is reduced. Two species that we know have gone through bottle-necks, elephant seals and cheetahs, have pretty much exactly the same mating systems as their near relatives that haven't experienced known bottle-necks.

I'd suggest that mating systems be considered solutions to past fitness tests

The genetics that make mating systems heritable may be assumed to always subject to mutation and selection, but the variations are also some of the most conserved heritable features of a species.

Mating systems (monogamous vs polygamous) emerge as the myriad simultaneous fitness problems are solved in the evolutionary history of a species. What is seen today is the current end-product of the 'ghost' of past fitness tests. Those fitness tests act on mating process, embryonic processes and post-embryonic developmental and maturation processes.

Selection pressure doesn't necessarily begin or end with number of sexual partners with which individuals successfully copulate.

The developmental condition of the offspring (altricial-relatively helpless at birth vs precocial-relatively independent at birth) places signigicant burderns on parent(s). Selection for survival of the offspring is not just on the 'infants' it is also on the adults via patterns of paternal care.
This characteristic developmental state of the newborn is both a solution to survival problems and a biotic platform that is acted upon by selection, for atricial offspring such as human babies, it can only work with the concomitant availability of 'workable' phenotypes produced by 'workable' genetic variation in the parent(s).

Parental care may include provisioning with food, providing protection, transportation or shelter. And particularly in humans, it includes the endowment of offspring with culture that promotes in broad ways to the fittness of the offspring and the perpetuation of the genetic lineage of both parent and offspring. The demands of parental care have many requirements/costs.

Mating systems represent workable solutions to the fitness costs and fitness benefits to producing a successful generation of offspring.

Monogamous mating systems, and variations on parental care that can include both-sexes cooperation in parenting are also representation of workable, heritable solutions.

[cthulu2016]

25. Nicely written.

I would add, not to open a whole 'nother can of worms, that our absolutely absurd level of infant helplessness marks human intelligence as a run-away sex-slective trait. There is no way we would have come up with something as crazy as a five, six, eight year effective infancy just to make our brains so big as a method to find food or evade predators.

It has to be like antlers and swallowtail feathers and peacock tails... our brain is too gaudy and costly to have arisen through adaptive environmental factors.

And it follows that we didn't become so big-brained until we were clearly without real natural enemies. Some animals may eat people but we are no one's primary prey.

[Cleita]

14. My theory is that it only became important to have sons when we became

farmers, which lead to territorial wars, which meant we needed extra sons to send into battle to die in protecting our land. I believe this also became the start of the practice of polygamy in our society as a means of taking care of the extra women, who also were needed to breed more sons.

Of course the study of modern aboriginal societies doesn't always hold this as true as the environment and level of development towards our type of civilization seems to dictate both the rules of taking mates and which children from those unions will be the most important.

In modern societies, like the Chinese favoring of sons, it seems to be because they have forgotten over the millennia as to why this is important to them and it has become cultural phenomena.

[Igel]

16. Here's a question.

One that I have no real intent to check.

Find some cross-species comparisons for birth ratios. Do all species show a fairly even distribution, male/female, at a point soon after conception? Are some skewed towards males or females? (I think I remember hearing of species that could screen sperm or zygotes for sex, but I'm not a big fan of biology.)

For those with strong skews, is there a sound reason adduced by evolution or behavior that can account for it? Perhaps the males are flashier and get eaten more often. Perhaps they're smaller. Perhaps they're a primary food source for the females.

Overall, is there a tendency towards greater complexity, biological or social, for those with flat, nearly 50/50, distributions? Perhaps body size matters. Perhaps intelligence or adaptibility?

There is a small portion of paternal mtDNA passed along to offspring (those sperm contain mtDNA, after all, and their mitochondria aren't destroyed with ovum fertilization).

[cthulu2016]

21. For most species, the sex ratio is approximately 1:1

There is a lot of variation and a lot of ways that parents can skew the ratio depending on the environment -- some birds can change the sex of embryos by heating them differently, humans can abort, etc. My impression is that for mammals, species wide, anything more extreme than 100 0 is unusual and unstable, but within groups it can be quite different. Small groups of Rhesus monkeys produce almost twice as many daughters, larger groups slightly more sons. It's amazing that they "know" how much room they have to gamble, since daughters are safer bets.

But though an environment can favor one over the other, in the big picture all sexual species seem to oscillate around 1:1 as the evolutionarily stable "sweet spot"

[TexasProgresive]

26. This from an earlier post of mine

The chart in the link does not reflect birth or conception ratios but starts with an equal number 100,000. The males start declining immediately which increases at adolescence.

At birth there is a higher percentage of males to females. This starts shifting right from the beginning. The link is to an actuarial life table that shows the chance of dying in each year of birth. for males it begins higher and becomes radically higher in the teens. That would be from risky behavior but the death rates for males remain higher until the unrealistic age of 116.

There could be any number of factors as to why. Here some possibilities:
1) There is an inherent weakness in the male that leads to early death.
2) It takes fewer males to propagate the species.
3) Males more likely to engage in risky behavior.
3) Longer living females ensure offspring growing to adulthood.

http://www.ssa.gov/oact/STATS/table4c6.html

[2ndAmForComputers]

27. How a sperm cell is formed has to do with it.

Normal male body cells have a X chromosome and a Y one. Sperm cells have only one X or only one Y, and they are made out of one specific kind of normal body cell, when its chromosomes are divided. The process is called Meiosis.

You can see how it's hard not to have the same number of X and Y sperm cells made.

[cthulu2016]

33. True, but that is not the mechanism

Any sex ratio is possible within the framework of an even number of X and Y sperm. In human the male sperm are much, much better at their job and manage to reach an ovum at a 170:100 ratio. But since a large number of male fetuses spontaneously abort, by birth the ratio is down to 105:100. And after birth down to 1:1.

In our case, since the X and Y production is fixed at 50-50, in order to acheive the evolutionarily optimal (or most stable) ratio of individuals (1:1) has involved selection of super-motile male sperm to overcome the high failure rate of male fetuses. The point being that the sex ratio is not an effect of the fact that the sperm types are 50-50 (and you're quite correct that they are 50-50 and that it would be hard to change)

That means that if we waved a magic wand and made the sperm ratio 75% female and 25% male evolution would, over time, handicap female sperm or enhance male sperm in such a way that we would still end up at a practical 50-50.

And if bears ate 90% of male children at age five we would, over time, see male birth outnumber female births 10:1. And so on.

[Another Bill C.]

29. Mitochondrial DNA

is passed on to both sexes by the mother. Y-dna is passed on male to male only.

[yurbud]

32. Wikipedia has a sortable chart on gender ratio: more guys at birth, more gals after 65

I demand a recount!

I'll just try to outlive the other guys and have a harem in the nursing home.

LINK: http://en.wikipedia.org/wiki/List_of_countries_by_sex_ratio

[cthulu2016]

35. And with the 1:1 crossover ocurring

during breeding age. Just as it should be. (Evolutionarily speaking.)

[yurbud]

36. I just realized this balances out a biological injustice:

Women can only reproduce to a certain age, but guys can fire live rounds until we're dead, but we die sooner.

Or maybe that just adds to natures trick on women: we can start the baby, but women have to take care of them after we pull the ultimate disappearing act (death).

[unkachuck]

41. I have a question....

....why do males have nipples?

[JCMach1]

43. Except now in some places... like India and China

women are choosing to selectively abort female fetuses...

that can change the ratio game mightily...

Most people know China and northern India have unnaturally large numbers of boys. But few appreciate how bad the problem is, or that it is rising. In China the imbalance between the sexes was 108 boys to 100 girls for the generation born in the late 1980s; for the generation of the early 2000s, it was 124 to 100. In some Chinese provinces the ratio is an unprecedented 130 to 100. The destruction is worst in China but has spread far beyond. Other East Asian countries, including Taiwan and Singapore, former communist states in the western Balkans and the Caucasus, and even sections of America’s population (Chinese- and Japanese-Americans, for example): all these have distorted sex ratios. Gendercide exists on almost every continent. It affects rich and poor; educated and illiterate; Hindu, Muslim, Confucian and Christian alike... http://www.economist.com/node/15606229