Why are there more females than males in the animal kingdom?

[needimprovement]

What is the scientific explanation for this?

[D H]

First things first: What makes you think that this is the case?

[Sisyphus]

There are?

[Moontanman]

Well if it's true it could be because in many animals females can reproduce with out the need for males...

[Maximus Semprus Veridius]

I'm not positive on the subject, however I think I do agree that there are more females than males in the Animal kingdom. If this is the case (which isn't a cetainty ofc) then if you think of females as being able to produce new members of a species through egg-laying or what-not they can only "focus" (I don't know the correct word) on rearing those offspring. A male on the oher hand can go and impregnate as many females as they want, so, One male can impregnate an almost limitless number of females, whilst females can only rear eggs from one male. Sorry I don't think I did very well explaining there, but I hope it helps.

[Mr Skeptic]

What is the scientific explanation for this?

 

If it is true (where's your source?), then I think the social insects might be enough of an explanation.

[skyhook]

Some creatures like daphnias and aphids seems to have more females. and also ants, termites and bees. but generally, it it hard to determine if there are more females or males in the animal kingdom. because of the large numbers of different creatures. Some reptiles sex are dependent on temperature when the eggs are in the nest buried in the ground, so it probably fluctuates with the changes in the environment. and some fish can change sex, like some colourful fish in the coral reefs. When a male is taken out of a group. Another one change to male and take over the group of fishes. and some fish it is the female that is the dominant one.

[needimprovement]

If it is true (where's your source?), <snip>.

Just learned from the world fact book it is 1.049 male/female at birth, but 0.803 at age 65 and over (as expected, because females on average live longer). It is 0.994 for the total population.

 

Based on the following data:https://www.cia.gov/library/publications/the-world-factbook/fields/2018.html

[Mr Skeptic]

Well there's the problem then. You can't extrapolate data on humans to the entire animal kingdom.

[needimprovement]

Some creatures like daphnias and aphids seems to have more females. and also ants, termites and bees. but generally, it it hard to determine if there are more females or males in the animal kingdom. because of the large numbers of different creatures. Some reptiles sex are dependent on temperature when the eggs are in the nest buried in the ground, so it probably fluctuates with the changes in the environment. and some fish can change sex, like some colourful fish in the coral reefs. When a male is taken out of a group. Another one change to male and take over the group of fishes. and some fish it is the female that is the dominant one.

I agree with you. It depends, some animals can change their sex based on environmental conditions. Nile crocodiles for instance, where the sex is determined by the temperature during embryonic development. Some nematodes live as hermaphrodites, where males are generated spontaneously 0.01% of the time.

 

Well there's the problem then. You can't extrapolate data on humans to the entire animal kingdom.

I'm not aware of data resources on sex ratios in specific species. Let's focus on humans instead.

Edited September 28, 2010 by needimprovement

[ccdan]

Let's focus on humans instead.

the difference is too small to have an explanation... it's something random and it happens that at this time there are more females than males (apparently at least)

[Sisyphus]

So the question is why do women have a longer life expectancy than men?

[Moontanman]

If the number of females in humans is great enough to be significant i would think it's an evolutionary echo of the time when females died more often due to child birth so populations that had more females were more likely to successfully reproduce....

[Sisyphus]

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

 

and more specifically,

 

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

[ccdan]

So the question is why do women have a longer life expectancy than men?

maybe because they have less dangerous jobs, get less often into physical fights, drink less alcohol, eat less fat and other unhealthy things, smoke less, like guns and other weapons less, are far less aggressive and take fewer risks in dangerous situations, use pills (likely to fail) for suicide instead of blowing off their brains or jumping off from buildings, drive less fast, etc? all in all there are fewer risks in their lives due to their far less aggressive and more healthy lifestyles... men on the other hand do the opposite and are more likely to lose their lives sooner..

[Marat]

Arne Hoffmann, 'Sind Frauen Bessere Menschen?,' makes a good argument that much of the shorter life expectancy of men can be accounted for by the greater risks they are expected by society to endure. Working in coal mines, the police, the fire service, and the military is still a role occupied predominantly by men. Society has always followed the rule of 'women and children first' in any disaster, which also cuts down on male life expectancy. Since feminists are now rigorously searching through every social institution to detect the structural discriminations against women in them, it is only fair to note that the discriminations are not all on one side.

 

I agree with the earlier poster that since the survival of most species depends on the number of females, who constitute a bottleneck on the breeding capacity, rather than males, who can each impregnate thousands of females, having more female births is favored by Darwinian pressures. Also, women are physiologically more stable than men and much more concentrated in the center of the Bell curve of distribution for any feature you can imagine, which also maximizes the number of women who will be healthy enough to breed. This is why Nobel Prize winners are almost exclusively male, while institutions for the severely mentally disabled are predominantly male. Similarly, for many inherited diseases such as hemophilia, women are carriers but men are the ones affected. In men, nature can afford to take gambles with more extreme features, since a few males so freakishly malformed that they can't breed won't hurt the survival of the species very much.

 

One the strangest phenomena in male:female sex ratios is that the percentage of male births always increases markedly after a major war in which large numbers of men are killed. How do the eggs and sperms know that they should respond to this loss in the male population?

[pioneer]

This suggests that the brain plays a role, since the brain is more aware of the need. Neurons do not undergo cell cycles as much as other cells. Neurons are designed to be less effected to DNA replication mutations, by default. These differentiate, via branching and synapses via external potentials. There is a forward pressure to the DNA, or else real time experience could not induce the differentiation changes. The brain is wired everywhere in the body, especially to the areas associated with reproduction. When such need arises, the DNA sees the forward neural pressure to make more males.

Edited September 28, 2010 by pioneer

[ewmon]

Why are there more females than males [in humans]?

One prominent idea is that the "secondary sex ratio" of 105 (ie, 105 males to 100 females) at birth drops to a "tertiary sex ratio" of ~100 (ie, 1:1) during the childing bearing years due to the higher mortality rate for males than for females, even in infancy (ie, seemingly before boys become more rambunctious than girls). The theory pointing toward the target of 1:1 during child bearing years is further supported by the fact that the "primary sex ratio" at conception is even more skewed in favor of males than is the secondary sex ratio (I have seen studies stating that it is 115, 138, and higher) supposedly due to more males suffering spontaneous abortions, stillbirths, etc. It's tough being male!

 

This pdf from the University of Idaho is interesting, and it also touches on why females live longer.

 

Only where overall life expectancy (ie, males and females combined) drops below ~45 years (ie, in Afghanistan and some African countries), do males outlive females (and then, not by much ... ~1 year).

[AnimeScientistMewtwo]

Well, personally, I don't know. In countries like Japan,CHina and other Oriental nations, there is the very amazing trend that both females and males of the population live to an extremely old age, 100,102,108 even. So, we should ask ourselves: HOW do women (and sometimes men) outlive others? Certain genomes? Enviroment? Animals(Animals help in lowering blood pressure) ?

 

I fear that there is more to this question. Perhaps, yes, males tend to be agressive, and yes, they do (mis)use alcohol, but one glass of red wine a day is good for the heart. So, perhaps there is a genetic leaning to the issue. Does enviroment play a role? Do animals contribute to long life, by lowering blood pressure? Is personality a key factor?

 

 

maybe because they have less dangerous jobs, get less often into physical fights, drink less alcohol, eat less fat and other unhealthy things, smoke less, like guns and other weapons less, are far less aggressive and take fewer risks in dangerous situations, use pills (likely to fail) for suicide instead of blowing off their brains or jumping off from buildings, drive less fast, etc? all in all there are fewer risks in their lives due to their far less aggressive and more healthy lifestyles... men on the other hand do the opposite and are more likely to lose their lives sooner..

[Dak]

iirc, don't hormones play a part: either male hormones causing cancer, or female hormones preventing it. This is why there's an increase in death-rate in females after the menopause (when their hormone levels become less different than males).

 

might be remembering wrong...

[AnimeScientistMewtwo]

My dad's gynocologist, I'll ask him