What would cause males to evolve to want the females to mate with other males?

Males use mate sharing as a bonding method for males and to combine their bloodlines with unrelated males to gain beneficial traits with other males. When no females are around they reproduce by androgenesis.

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    $\begingroup$ Which females? Females they mated with before? Females of their family? Females of their tribe? Females who are complete strangers? Also, if every single male would say "Please mate with someone else, but not with me", then there could only be mating without the consent of the males. $\endgroup$
    – Philipp
    Aug 9 at 14:55
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    $\begingroup$ This is a very broad ask that is soliciting an open ended list of answers. Such questions are too broad for this site. $\endgroup$
    – sphennings
    Aug 9 at 15:07
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    $\begingroup$ I enjoyed answering this question! But I'd like to remind you that you need to provide as much detail as you possibly can. This Q would have benefited from knowing (a) more about the biology of your species. (b) More about the developmental stage of the species (are they frogs waiting to evolve into apes or are they c. 1250 medieval peoples fighting off the Plague?). (c) More about the context of your Q (are we modifying our world or building yours?). (d) More about your expectations and requirements for the answer. For a new user, the Q was good enough, but please get into the habit. Thanks! $\endgroup$
    – JBH
    Aug 9 at 17:29
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    $\begingroup$ The second paragraph is confusing. Explain it more. What is "androgenesis" $\endgroup$
    – Daron
    Aug 9 at 17:39
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    $\begingroup$ @Wyck Oh, I misread this as being your question. But you only edited it. $\endgroup$
    – Daron
    Aug 10 at 14:24

4 Answers 4


Group fitness.

The males who want this are old. Their mating days are largely done. But they are shrewd operators as regards advancing the cause of their families. These old males have sons and nephews and brothers. They want to control the reproduction of young females such that these younger males related to them are the fathers of any babies who are born. They want the females to mate with these younger males related to themselves because then their bloodline carries on.

Evolutionarily that is a good strategy, even for nonsentients. The genes in old males who want to control female reproduction are the same genes in the young males who will be the fathers. Someday some of those young males will be old and take up the new role.

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    $\begingroup$ And isn't this pretty much how RL works in many cultures! $\endgroup$
    – elemtilas
    Aug 9 at 17:35

I'm assuming you're creating a rule of evolution for your imaginary world and are not trying to modify known evolution in the Real World

The problem with modifying the rules of evolution in the Real World is that Earth's evolutionary pattern is one of competition and the "path of least resistance." The critters that could gather the food, protect themselves, get mates... and do that more efficiently than some other critter... they're the critters who survived to evolve. The idea of giving something away (and giving away your ability to propagate is a big one) simply doesn't come into play in Terrestrial evolution.

But let's ignore that. It's boring.

I am going to make one assumption. You didn't explain, but it seems this question is only valid if there is a bonded pair, a married couple, if you will, and that bonding/marriage/union is desirable as a species (and not just as a governmental, legal, or religious construct).

1. Shift the focus from families to communities

Monogamy in the terrestrial animal kingdom is fairly common. Animals pair up and stay paired up at least for the season, but often for life.<citation needed> This isn't because animals have developed complex philosophies and religions. It's because a bonded pair can more easily defend themselves against the vagaries of life. It's more common to defend one's family from various problems within your own community than it is against those from another community.

But let's reverse that on your world! Let's assume, for the sake of argument, that shared breeding produces a community-specific marker. let's say a common pheromone. You can literally identify which community a single member is from because that member has a smell that's shared with every member of the community. And each community's smell is different. In this case, competition is believably shifted to between communities. Consequently, it's favorable for females to bear as many children from as many males as possible to promulgate and strengthen the community. The tendency would be to promote greater harmony within the community because competition has been shifted to between communities.

That genetic marker can be anything. A smell, a color, a size, an extra toe... anything, so long as it creates the us vs. them condition that evolution requires to, well... promote evolution.

2. Let's change the nature of conception to shift the idea of children being "mine" to being "ours"

Here on Earth one issue driving evolution is that children are a limited resource. For example, human females are good to have 2–6 children, but rarely have 6–12 and very rarely more than 12. Children are a fairly rare commodity. The chance to propagate who you are has a narrow window for success. From an evolutionary perspective, the drive to be a part of that propagation is very strong, leading to competitive selfishness for mates.

But what if your females can have more children, remain fertile longer, or both? Suddenly the pressure to be the only propagator is less. This has consequences, like really large populations, which could be moderated by shortening the average lifespan... but maybe there's a better idea.

What if we reverse the nature of conception? Here on Earth females have a narrow window for bearing children (fixed number of eggs, eggs available only periodically, etc.) but the males can fertilize eggs basically starting from puberty and at-will until they die. So, let's reverse it. It doesn't matter if you change how many eggs your females have or how often they're available for fertilization—just change the male's contribution to something that's infrequent or even rare. Using Earth's humans as an example, the idea is to change the male so that he isn't available/able to fertilize eggs every month.

Suddenly the species requires polyandrism just to survive.

3. On your world, immunity to disease found a different path than here on Earth.

Finally, here on Earth evolution solved the problem of disease by creating an absolutely amazing immunity system. While some immunity is passed from mother to child, most of the system is designed around the individual's ability to internally detect, analyze, and defeat disease.

But what if on your world it took another path? Rather than the direct attack method we Terrans use, what if your world evolved an innoculation-based solution? In other words, the immunity passed mother-to-child is much more important in your world than here. The idea is that the chance of any individual developing a resistance to disease is much lower than here on Earth—but the ability to transmit that resistance to the next generation is much higher than here on Earth.

Which means the protection of the species depends on females mating and conceiving with as many males as they can. A negative is that epidemics will be more immediately devastating because it takes at least a generation to push the solution through the ranks. But that would lead to evolution favoring females that conceive easily, bear quickly, and have the higher tendency to healthy offspring.

(In this case, limitations on the number of bonded males would come about through the development of civilization, law, and the tendency for one person to think they have the right to stick their nose into another person's business).

  • $\begingroup$ Wait... did you just 'citation needed' your own post? Duuuuuuude! $\endgroup$
    – Corey
    Aug 10 at 3:48
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    $\begingroup$ @Corey I know when I don't have the time to prove my point! $\endgroup$
    – JBH
    Aug 10 at 11:14
  • $\begingroup$ I would say that social animals have the highest chance of males asking others to share their mates. Social animals already share a lot of things in order to survive, like food, guarding offspring even if it isnt your own, protecting territory, who engages intruders and why etc. As long as you've already had a surviving child with your chosen mate it makes sense to ask other males to mate with her as well: if they extend the same courtesy you have more chance of creating genetically diverse offspring with various partners, which makes the group stronger. $\endgroup$
    – Demigan
    Aug 10 at 13:08

What if females could only have one child with each male in their life, but there is an evolutionary advantage in having a lot of siblings?

In that case males would encourage a female they already have a child with to mate with many other males, so their offspring enjoys the help and protection of a large number of siblings.

Keep in mind that having a lot of step-children is usually an evolutionary disadvantage, because they are going to compete with the offspring for resources. So you would need to come up with a reason why half-siblings are an advantage in your world. For example, half-sibling groups could engage in direct battle with the children of another female, so the stronger half-sibling group will prevail.

  • $\begingroup$ I like this because I can see it happening for non-fitness reasons - something like the immune response triggered by the Rh factor such that the first child is fine, but any subsequent pregnancies are in danger. So basically each female has to pick a new male for each pregnancy. Or it could be behavioural: I’m told this is how it works with opossums raised in captivity (once a male is separated from a female, she will refuse to mate with him again, so breeders have to keep a rotating stable of males) $\endgroup$
    – Ottie
    Aug 10 at 14:07

Genetic Diversity

Immaculate specimen of manhood as I am, I would still rather you you mate with my brother and not me. My brother would rather you mate with me and not him.

Fortunately we are best friends as well as brothers. So when the ladies roll by we team up and fight off the ladies and they don't mate with either of us.

Good thing too. Since all those ladies are our sisters and cousins. And that big one in the back with the hairy knuckles and look of bloodlust is our dear old mother.

You see everyone in the tribe is related. My brother is your cousin and my aunt is your sister AND your cousin. This tribe needs to introduce new blood to prevent inbreeding.

This is done by finding wandering males who are expelled from their tribes and mating with those guys.

The wandering males don't like this but they are alone. They are overpowered and their genetic material is extracted.

Sometimes the new males get added to the tribe and then they don't have to breed anymore.

  • $\begingroup$ This behavior existed on Iceland by the past. Icelandic woman had the reputation to be very "friendly" with sailors accosting to their country. $\endgroup$ Aug 10 at 9:32
  • $\begingroup$ Death by snoo snoo. :D :o :D :o First the large women, then the petite women, then the beautiful women, then the large women again. $\endgroup$
    – DKNguyen
    Aug 20 at 4:43

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