Are Males Really the Dominant Sex in All Species?

[pivoxa15]

Someone claims that males are the dominant sex in all species (not just phenotype but genotype as well) and so offsprings will on average be more likely to be males than females. Hence in the very long term, males will slightly outnumber females in all species.

Morever, he claims that when you get breeding between two people from different race, the offspring will on average look more like the father than the mother.

Is this person wrong in both claims?

 

[Monique]

Absolute nonsense, there are many species where females are dominant (think for instance the black widow spider). In humans females slightly outnumber males, since males are more likely to die in utero. I have heard that fertilizations producing males are more common, but that is set back by the loss of males in the uterus.

I don't know whether offspring are more likely to look like their mother or father, I don't think that is true.

 

[arildno]

Of human births, approx. 51.4% are males, I think.
Due to higher mortality rates for males, about 50/50 is reached upon maturity.

 

[selfAdjoint]

Consider the social insects, ants and bees. The sex ratio there is thousands to one of (sterile) females to males.

 

[pivoxa15]

I suspected that this person was wrong. For humans, do the experts agree that it is 1/2 probability for males and females?

 

[pivoxa15]

Of human births, approx. 51.4% are males, I think.
Due to higher mortality rates for males, about 50/50 is reached upon maturity.

I susupect that the slightly higher percentage (than 50%) for male births is because of countries with child restrictions policies to favour males more hence tend to give more birth to males.

 

[Monique]

Consider the social insects, ants and bees. The sex ratio there is thousands to one of (sterile) females to males.

Do you mean the worker bees/ants? Those grow from unfertilized eggs, they are haploid organisms.

 

[selfAdjoint]

Yes, but they certainly aren't males! What is the ratio of queens to drones? Do you know?

 

[pivoxa15]

So is the conventional view for male/female birth 50/50? If so what is the basic science behind it?

 

[selfAdjoint]

Everyone has two sex chromosomes, which come in two types: X and Y. Those with two X's are female, those with an X and a Y are male. Two Y's do not make a viable fetus, and I ignore occasional oddities with three or more sex choromosomes.

Now when a sperm is formed it will have one of the two chromosomes from the male, that is, either an X or a Y. It is a random chance which anyone sperm gets. And when an egg is formed it gets one of the two chromosomes from the female, which in this case is sure to be an X. So when the zygote is formed from the union of the sperm and the egg, it will have two sex chromosomes; one is certain to be an X and the other has a 50-50 chance of being a Y or an X. This leads to a sex ratio of 50% males and 50% females.

In practice this is affected by a number of variations, from differential motility of the X- and Y-bearing sperm to the in utero and post birth viability differences of the two sexes. The upshot is that slightly more than half the babies born are boys, and by the age of (I think) 20 the two sexes are equal in numbers.

 

[SciFiGuy]

Someone claims that males are the dominant sex in all species (not just phenotype but genotype as well) and so offsprings will on average be more likely to be males than females. Hence in the very long term, males will slightly outnumber females in all species.

In mammals, males have one sex chromosome of each type (XY) and females have two of one type (XX). In birds, males have two of one type (ZZ) and females have one of each (ZW). In some reptiles, sex determination isn't genetic at all, but based on incubation temperature. And even there, it varies. Alligators, for instance, have "hot males" - a hotter nest produces males. Sea turtles have "cold males" - colder nests produce males.
Given the variety here (and that's without leaving the vertebrates), I seriously doubt that there's any hard and fast rule about male predominance.

 

[pivoxa15]

Everyone has two sex chromosomes, which come in two types: X and Y. Those with two X's are female, those with an X and a Y are male. Two Y's do not make a viable fetus, and I ignore occasional oddities with three or more sex choromosomes.

Now when a sperm is formed it will have one of the two chromosomes from the male, that is, either an X or a Y. It is a random chance which anyone sperm gets. And when an egg is formed it gets one of the two chromosomes from the female, which in this case is sure to be an X. So when the zygote is formed from the union of the sperm and the egg, it will have two sex chromosomes; one is certain to be an X and the other has a 50-50 chance of being a Y or an X. This leads to a sex ratio of 50% males and 50% females.

In practice this is affected by a number of variations, from differential motility of the X- and Y-bearing sperm to the in utero and post birth viability differences of the two sexes. The upshot is that slightly more than half the babies born are boys, and by the age of (I think) 20 the two sexes are equal in numbers.

Why is there a slightly more than half of babies being boys. What is the science behind it? It looks like this person is correct for humans as least.

 

[arildno]

Why is there a slightly more than half of babies being boys. What is the science behind it? It looks like this person is correct for humans as least.

One possible explanation is that X-chromosome bearing sperm cells have slightly more mass than the ones bearing an Y-chromosome (since the X is bigger than the Y), and hence, one might expect that the Y-guys are slightly faster on average than the X-guys. (This would be a variation of the motility difference nemtioned by SA)

This, however, is not,I believe, regarded as more than a speculative hypothesis. The issue is not as yet definitively resolved.

 

[pivoxa15]

One possible explanation is that X-chromosome bearing sperm cells have slightly more mass than the ones bearing an Y-chromosome (since the X is bigger than the Y), and hence, one might expect that the Y-guys are slightly faster on average than the X-guys. (This would be a variation of the motility difference nemtioned by SA)

This, however, is not,I believe, regarded as more than a speculative hypothesis. The issue is not as yet definitively resolved.

That is interesting. In a book called "Are Men necessary", it claimed that because of the fact that there are only one Y chromosome, when it goes bad from mutation, it cannot repair itself hence the average rate of decay will see the Y chromosome disappear in around 10 million years - with it the male population. I have not read the book but only saw it in a review. Its true that this issue is highly debatable.

 

[SciFiGuy]

That is interesting. In a book called "Are Men necessary", it claimed that because of the fact that there are only one Y chromosome, when it goes bad from mutation, it cannot repair itself hence the average rate of decay will see the Y chromosome disappear in around 10 million years - with it the male population. I have not read the book but only saw it in a review. Its true that this issue is highly debatable.

Hmm...I'd heard that the Y chromosome contained less information per length than normal, because it repeats so that it can cross-check against itself.
Who knows. I'm an ecologist because I hated all that micro stuff.

 

[pivoxa15]

Hmm...I'd heard that the Y chromosome contained less information per length than normal, because it repeats so that it can cross-check against itself.
Who knows. I'm an ecologist because I hated all that micro stuff.

Obiously there is some resistance but it is not as good as having a copy of yourself next to you - like the X chromosomes. The resistance might be the reason why it will take 10 million years and not sooner.