# Any animals with male/female births not 1/1? **URL:** \ **Category:** Factual Questions\ **Created:** [August 10, 2013, 4:26pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875 "2013-08-10T16:26:25Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [August 10, 2013, 4:26pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/1 "2013-08-10T16:26:25Z")
I think this must be a common fantasy, seeing how often this situation crops up in fiction - due to war/natural disaster/quirk of nature, one sex now greatly outnumbers the other. Changes in social norms and living arrangements must be made, blahblahblah. I think it was mentioned in one of David Eddings’ books Anyway, I then heard that this situation is self-correcting, because if one sex outnumbered the other, any mutation that produced more of the rarer sex will spread quickly, bringing the ratio back to 1. So, is this always the case? Any species with more births of a certain sex? All I can think of are ants and bees. And don’t some frogs’ sex change with temperature? Any more “advanced” animals? ---
**Author:** ![Tamerlane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tamerlane/32/7602_2.png) [@Tamerlane](https://boards.straightdope.com/u/Tamerlane)\ **Post date:** [August 10, 2013, 4:42pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/2 "2013-08-10T16:42:54Z")
> [@AaronX](#): > > So, is this always the case? Any species with more births of a certain sex? All I can think of are ants and bees. And don’t some frogs’ sex change with temperature? Any more “advanced” animals? [Temperture dependent sex determination](http://en.wikipedia.org/wiki/Temperature-dependent_sex_determination). To that you can add [parthenogenesis](http://en.wikipedia.org/wiki/Parthenogenesis#Reptiles) as another possibility - in whiptail lizards in particular the parthenogen females so produced can still reproduce sexually with males of closely related species [as shown here](http://ilarjournal.oxfordjournals.org/content/45/1/46/F1.large.jpg). ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 10, 2013, 5:01pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/3 "2013-08-10T17:01:52Z")
> [@AaronX](#): > > Anyway, I then heard that this situation is self-correcting, because if one sex outnumbered the other, any mutation that produced more of the rarer sex will spread quickly, bringing the ratio back to 1. This is expressed in [Fisher’s Principle](http://en.wikipedia.org/wiki/Fisher%27s_principle), that states that sex ratios will tend to 1:1 because each sex contributes equally genetically to the next generation and thus is equally valuable to a parent. (More precisely, there will be equal parental investment in each sex. For example, if males are more “expensive” to raise to adulthood, then fewer males may be produced compared to females.) > [@](#): > > So, is this always the case? Any species with more births of a certain sex? All I can think of are ants and bees. And don’t some frogs’ sex change with temperature? Any more “advanced” animals? In social insects the principle doesn’t apply to sterile workers. Reproductives will be produced at a 1:1 ratio, taking into account any differences in how much energy it takes to produce each sex. Many fish are sequential hermaphrodites. All members of some species start out as one sex, then change to the other at a certain size, or if they are the dominant individual in a group. Which sex changes to the other depends on the relative reproductive advantages of large females vs large males in that particular species. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [August 10, 2013, 5:05pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/4 "2013-08-10T17:05:02Z")
Bees? ---
**Author:** ![Filbert](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/filbert/32/3433_2.png) [@Filbert](https://boards.straightdope.com/u/Filbert)\ **Post date:** [August 10, 2013, 5:15pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/5 "2013-08-10T17:15:53Z")
> [@Colibri](#): > > In social insects the principle doesn’t apply to sterile workers. Reproductives will be produced at a 1:1 ratio, taking into account any differences in how much energy it takes to produce each sex. Sorry, but this is not true for bees- several hundred drone (male) bees may be produced in a year, but only a few (maybe 10 or so) queens. Incidently, if the queen is lost, worker bees will actually start laying viable eggs. These will all be male, as the workers haven’t mated, so they’re not truly sterile either. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [August 10, 2013, 5:50pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/6 "2013-08-10T17:50:03Z")
In the case of dogs and many other mammals the sex of the child is heavily influenced by the relation to what part of her cycle she was in when she mated. A very early breeding of dogs will usually produce all females. If she produces all females it will increase the compettion and lead back to a proper ratio. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 10, 2013, 5:58pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/7 "2013-08-10T17:58:00Z")
> [@Filbert](#): > > Sorry, but this is not true for bees- several hundred drone (male) bees may be produced in a year, but only a few (maybe 10 or so) queens. You’re talking about honeybees, rather than bees in general. Honeybees are unusual in that they reproduce by colony fission. In accord with Fisher’s principle, [it has been proposed that male biased sex ratio can be explained by the fact that the workers that accompany the queen represent part of the parental investment in females.](http://www.jstor.org/discover/10.2307/2460102?uid=2&uid=4&sid=21102525546941) ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [August 10, 2013, 6:09pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/8 "2013-08-10T18:09:41Z")
Of course, with modern dinosaurs, it doesn’t matter even if they’re all female. 😃 ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [August 10, 2013, 6:18pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/9 "2013-08-10T18:18:43Z")
> [@HoneyBadgerDC](#): > > In the case of dogs and many other mammals the sex of the child is heavily influenced by the relation to what part of her cycle she was in when she mated. A very early breeding of dogs will usually produce all females. That is remarkable. I must ask: cite? ---
**Author:** ![Filbert](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/filbert/32/3433_2.png) [@Filbert](https://boards.straightdope.com/u/Filbert)\ **Post date:** [August 10, 2013, 6:47pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/10 "2013-08-10T18:47:44Z")
Yes, I should have specified honeybees. Not really convinced by that proposal though, I’ve come across it before, and it does look a bit like “I’m going to prod data until it does what I want”… Still, there are several species of invertebrate that are entirely, or almost entirely, female- for example some stick insects have no known males, and some have a sex ratio of thousands to one, and daphnia normally reproduce parthenogenically, and only produce some males in severe conditions (after mating they lay eggs which can remain dormant until conditions improve). Basically any species which can reproduce by parthenogenesis can wind up with very unequal sex ratios, even if that isn’t necessarily great for long term species survival. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [August 10, 2013, 7:01pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/11 "2013-08-10T19:01:51Z")
IIRC, there’s a mutation in insects that causes only males to be hatched; it’s carried in male eggs and poisons female eggs. It’s a single gene mutation so it spontaneously appears on a regular basis, and spreads itself efficiently by eliminating all competition, despite its ultimately self defeating nature. It follows a cycle of appearance via mutation-\> rapid spread-\> population collapse when there aren’t enough females. There’s also a parthenogenic wasp species that hatches only females because of the influence of a bacterium; eliminate the bacterium and they can produce males. I recall that one because a scientist quipped “penicillin can cure virgin birth.” ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 10, 2013, 7:23pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/12 "2013-08-10T19:23:21Z")
> [@Der\_Trihs](#): > > There’s also a parthenogenic wasp species that hatches only females because of the influence of a bacterium; eliminate the bacterium and they can produce males. I recall that one because a scientist quipped “penicillin can cure virgin birth.” Sounds like [Wolbachia,](http://en.wikipedia.org/wiki/Wolbachia) which is found in many insects and can produce weird distortions to the sex ratio. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [August 10, 2013, 7:35pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/13 "2013-08-10T19:35:57Z")
> [@KarlGauss](#): > > That is remarkable. I must ask: cite? As usual I stand corrected, I had read that and believed it for the past 40 years based on some of my old dog books. I can find nothing on that now. ---
**Author:** ![ratatoskK](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ratatoskk/32/2987_2.png) [@ratatoskK](https://boards.straightdope.com/u/ratatoskK)\ **Post date:** [August 10, 2013, 8:45pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/14 "2013-08-10T20:45:42Z")
See ‘human sex ratio’ in Wikipedia. More males are born than females. Personally I think males tend to have more health issues but that’s just my WAG. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 10, 2013, 8:58pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/15 "2013-08-10T20:58:40Z")
> [@ratatoskK](#): > > See ‘human sex ratio’ in Wikipedia. More males are born than females. Personally I think males tend to have more health issues but that’s just my WAG. Males tend to have a higher mortality rate for a variety of reasons, including being more prone to be killed in accidents, fights, warfare, etc. What counts with regard to evolution is the sex ratio upon reaching adulthood rather than that at birth. ---
**Author:** ![clairobscur](https://avatars.discourse-cdn.com/v4/letter/c/839c29/32.png) [@clairobscur](https://boards.straightdope.com/u/clairobscur)\ **Post date:** [August 10, 2013, 9:02pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/16 "2013-08-10T21:02:23Z")
The sex ratio in kakapos (a new zealand parrot) depends on the abundance of food (more males are born when food is more abundant). ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [August 10, 2013, 9:53pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/17 "2013-08-10T21:53:37Z")
This is often true in domesticated animals, but not naturally, rather as a result of human intervention. Often these animals are bred via artificial insemination, and the transported semen is treated to increase the likelihood of one gender. For example, in pleasure horses, mares are preferred. (Except in racehorses, but AI isn’t legal for racehorses.) In cattle, beef breeds prefer steers, while dairy breeds prefer heifers (obviously). For laying chickens, you need hens, but meat chickens are mostly male. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 10, 2013, 10:18pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/18 "2013-08-10T22:18:24Z")
> [@Colibri](#): > > Males tend to have a higher mortality rate for a variety of reasons, including being more prone to be killed in accidents, fights, warfare, etc. What counts with regard to evolution is the sex ratio upon reaching adulthood rather than that at birth. But the op did ask “births.” Not the point of the op but in humans in China and India today there is a male over-representation of births … a bit different in mechanism though. More to the op is [this article](http://rsbl.royalsocietypublishing.org/content/5/4/524.full) - > [@](#): > > The accepted average human natal sex ratio is slightly male biased, at 106 males per 100 females or 51.5 per cent males. Studies conducted on a localized scale show that sex ratios deviate from this average in response to a staggering number of social, economical and physiological variables. However, these patterns often prove inconsistent when expanded to other human populations, perhaps because the nature of the influences themselves exhibit substantial cultural variation. Here, data collected from 202 countries over a decade show that latitude is a primary factor influencing the ratio of males and females produced at birth; countries at tropical latitudes produced significantly fewer boys (51.1% males) annually than those at temperate and subarctic latitudes (51.3%) … [Some more human data](http://rspb.royalsocietypublishing.org/content/279/1739/2883.full) - famine apparently results in fewer males born. (IOW, not only in parrots.) ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 10, 2013, 10:52pm UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/19 "2013-08-10T22:52:42Z")
> [@DSeid](#): > > But the op did ask “births.” I was offering an explanation of _why_ there might be more males at birth. If one sex preferentially experiences greater mortality before reproductive age, this can produce selection for there to be an unbalanced sex ratio at birth in favor of that sex. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 11, 2013, 12:08am UTC](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875/20 "2013-08-11T00:08:01Z")
Those articles offer other explanations as well. Not just survival. In times of stress more males are born not only, according to the stated hypothesis, because males are less likely to survive, but because the investment pays better returns in stressful times: > [@](#): > > … parental investment in sons of good quality yields greater reproductive returns than comparable investment in daughters of the same quality, whereas parental investment in sons of poor quality yields lower reproductive returns than comparable investments in daughters of the same quality [1]. This leads to the prediction that for human and non-human vertebrates, healthy, well-nourished and high-status mothers are more likely to give birth to sons, whereas unhealthy, poorly nourished and low-status mothers are more likely to give birth to daughters [3–7]. Another important adaptive sex ratio adjustment hypothesis was proposed by Myers [2]. Myers agreed with TW on the prediction regarding the adaptive sex ratio adjustment but disagreed with their explanation. According to Myers, mothers under nutritional stress are more likely to give birth to daughters because daughters are nutritionally less expensive than sons and thus have a better chance to survive the harsh environment [2]. [Next page](https://boards.straightdope.com/t/any-animals-with-male-female-births-not-1-1/665875.md?page=2)