I just learned that because male moose are the only ones you’re allowed to hunt around here, the population has quadrupled in the last several decades. The reason is obvious, when you think about it - males are bigger, and consume more of the available resources, however, you only need a few males to impregnate a lot of females. I suppose there might be some inbreeding, but I can’t really see that it should have that much to say unless the ratio of males to females is extreme. Also, shouldn’t inbreeding be “self-defeating” in that as nasty recessive genes become commoner, they’re selected against?
So, why isn’t a high female to male ratio a more common evolutionary trick?
I think you answered your own question.
Hybrid vigour.
The bigger the gene pool the better. If you had a great many more males than females you would have a far greater number of siblings and first cousins in close proximity to one another.
What about combining it with a higher mutation rate? Anyway, the fact that the moose population has quadrupled shows that it works, at least in the short term. And since evolution doesn’t think ahead, why aren’t we seeing more of this?
Evolution doesn’t think or allow anything at all. If a given method works, without too many drawbacks, then that method will continue to work until a mutation occurs which is more efficient.
Because males are needed to protect and raise young. They gather resources for the family, like building shelter and collecting food. In species where this doesn’t happen, you don’t have a 1:1 ratio.
I am not sure that your “obvious” reason has been proven. Were the situation decades ago that moose weren’t hunted at all, then I think it would be plausible to say that removing only the males has increased the population. I suspect however that the primary effect is not that males are now being killed, but that females are now NOT being killed. It seems pretty straightforward to me that allowing more females to survive and reproduce will lead to greater population growth.
It is a common evolutionary trick, and where it isn’t present there could be any number of reasons. Males aren’t necessarily bigger or more resource intensive either, so that’s not a valid reason for a higher f:m in general.
Band name.
Many evolutionary “strategies” (not deliberate, as Lynn Bodoni points out) are predicated on the fact that in most species a terrible attrition takes place. Most of the individuals perish without leaving descendents. The details vary with the particular circumstances of the species, but in many the very point of having males is to let them take the brunt of the selection, leaving only the fittest (or luckiest) to propagate. In somewhat simplistic terms, if hunters and predators take so many moose a year, the males serve as comparatively expendable “decoys”, taking predation pressure away from breeding females.
I’ve never heard this before. Do you have a cite?
When every child has one male and one female parent, the best sex-ratio for the parents (in terms of maximizing the number of grandchildren) is one to one.
If one male fathers many offspring, that makes a male child potentially more valuable. A successful male child is like hitting the lottery for the parents–they’ll have many grandchildren. The math works out that the expected number of grandchildren is maximized if your children’s sex ratio is one to one.
Why does evolution allow so many males?
mother nature is misandrous or at least just mean.
Sex ratios are the result of evolution.
Here’s the simple explanation. Suppose we have a species with a male/female ratio of 1:10. Because it is mostly females, this species will produce almost twice as many offspring as a species with a 1:1 sex ratio.
But notice something interesting. Who gets to give birth to the males? If you have a female offspring, that female can be expected to produce on average one 2nd generation offspring. However, if you give birth to a male, you can expect that male to father ten 2nd generation offspring.
This means that any mutation that increases your chance of producing male offspring is strongly selected for, since males have 10 times the fitness of females.
And the reverse is true, if there are 10 males for every 1 female, females have 10 times the fitness of males.
So therefore, the equilibrium state is to put on average the same amount of resources into producing males as females, because when sex ratios are roughly even there is no advantage to producing either male or female offspring. As sex ratios skew, then there is an advantage to producing the rarer sex, and therefore the sex ratio returns to equilibrium.
Suppose that the ratio weren’t 1:1. Let’s say, for instance, that you have a species where, say, 3 in 4 births are female, while 1 in 4 births is male. In such a species, any given male is going to be, on average, three times as successful as any given female. So now let’s suppose that there’s an individual of this species for which the mechanism for favoring female offspring is absent, or even reversed: That individual’s offspring will be more male than normal for the species. Because that individual is having sons rather than daughters, and males are more successful than females, that individual itself will also tend to be more successful, and have more descendants. So the genes for having more male offspring will spread through the population, until you reach equilibrium of a 1:1 ratio.
Evolution would support more females over males if it worked strongly by group selection. In this case, the selection on the individuals far outweighs any benefits gained by group selection. Group selection is pretty rare when it comes to evolution.
Without delving into the math, the short answer why there’s not fewer males is that because each child needs to have one father and one mother, on average males and females are going to be equally successful with a 50/50 sex ratio. Even if 5% of the males get a harem of 20 females and the other 95% of the males get nothing, on average the males and females will have equal amounts of offspring.
If the ratio is skewed towards more females (or males), then the minority sex will have on average more offspring. So a mutation that favors more of that minority sex will have an advantage and spread through the population. The only stable situation is with a 50/50 sex ratio.
[There are going to be slight, minor complications, but the general idea is true, and that’s why most species have sex ratios fairly close to 1:1; remembering that individuals that will never mate (worker ants) don’t count]
Well in human populations you see issues when the male population is devastated. For instance Paraguay verus Argentina, Brazil and Uraguay. Or France during WWI.
Now those are more social issues than genetic, but you see there were significant issues when the male populations in France and Paraguay fell dramatically during those wars.
Suppose the male populations of a species gets wiped out? You’d need a bunch of the non-breeders to start breeding again to repopulate without genetic problems.
Also non-breeding males in many animal groups help the herds as a whole. They stand look out for instance. Obviously it varies in different animals. Some like the bees, the males are starved to death once food becomes scarce.
Are there any mammals where there is an imbalance between male and female offspring? The ‘strategy’ seems simple. A 50/50 mix is the best guarantee against ending up with all females or all males within a population.
You need a cite for something this obvious? Ask your daddy!
The Chinese?