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In the human species, one male partner is enough for the sperm to fertilize the egg. The average cargo is just one child, half of its DNA from the mother and the other half from the father. But there are cases when the fertilized egg splits into more than one, and that's where twins and triplets and so on and so forth are, in a nutshell, possible.

But let's say that twins or triplets are the result of one mother having her egg fertilized by two or three genetically distinct sperm from two or three different male partners within a three-day limit. Any higher a number is not immediately fatal, but it can still increase the risk of complications during pregnancy or labor.

There are some species of our fellow mammals that have that kind of sexual mechanics. Indeed, some species of primates have one mother having children from more than one male partner. So why don't we have that flexibility? Would it make sense to even try to have that?

No mention of fertility drugs, please. They are not considered natural human physiology.

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  • $\begingroup$ Exactly which animal can simultaneously carry children from multiple fathers? $\endgroup$ – AndreiROM Jan 21 '16 at 15:48
  • $\begingroup$ Birds can and do have multiple fathers per clutch of eggs, but birds also cheat in this regard: only one egg is laid every day or so. $\endgroup$ – Draco18s Jan 21 '16 at 15:49
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    $\begingroup$ @AnreiROM Cats can have kittens each with a different father in the same litter $\endgroup$ – evilscary Jan 21 '16 at 15:57
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    $\begingroup$ Humans can too, if the second dad is quick enough and there are multiple eggs. $\endgroup$ – Oldcat Jan 21 '16 at 23:16
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There are two kinds of twins, Identical, and Fraternal. Identical twins are the ones where 1 fertilized egg splits into multiple children. Fraternal twins are two separate eggs fertilized by different sperm. That is how a boy and a girl can be twins.

Now the easiest way is with fertility drugs, this can cause the woman to produce multiple eggs at a time. But this is also a natural phenomenon and is still relatively frequent. I have several fraternal twins in my family.

If a woman has sexual relations with multiple men during a month where she produces multiple eggs (fairly close together!), then yes, each child could possibly have a different father.

Added: This is why dogs and cats have litters and can have multiple fathers. When they go in heat dogs and cats produce multiple eggs to be fertilized.

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It happens

It's generally something that's more often discussed in the gutter press and by Jeremy Kyle, but superfoetation can occur in humans.

It may occur a lot more often that we're aware of, but the average person isn't in the type of relationship where it would be noticeable unless the babies born were clearly of different gestational ages.

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    $\begingroup$ Or racial differences, which is a common way this is identified. $\endgroup$ – PearsonArtPhoto Jan 21 '16 at 16:09
  • $\begingroup$ I'm referring to the event itself under "normal" circumstances, i.e. a single father. $\endgroup$ – Separatrix Jan 21 '16 at 16:13
  • $\begingroup$ That isn't clear, and if so, doesn't seem to answer the question... $\endgroup$ – PearsonArtPhoto Jan 21 '16 at 16:16
  • $\begingroup$ It's only half an answer, I haven't even gone into superfecundation yet, but I'm about to leave the office $\endgroup$ – Separatrix Jan 21 '16 at 16:18
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Actually, there is a strange possibility that I've heard of, that of the chimera. A chimera has two different sets of DNA and is a little like an organ recipient. I'm not sure if this is different eggs, with the remnant of a lost twin being absorbed. But it is fascinating--mothers who fail a maternity test for the baby born from their own womb are possible!

These two could be from different fathers, just as above--two fathers, without actual twins, if the absorbed twin was fraternal.

We do have that capability, but in this world it doesn't make sense because we are highly overpopulated right now. The only reason would be in the case of a person with extremely valuable traits--if we were to attempt a proliferating version of eugenics, as women are more limited in how many children they can have. A better way would be through the use of donor eggs, in my humble opinion--unless it is discovered that the transmission of desirable traits happens through the place of gestation, which seems unlikely to be a large effect if at all.

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  • $\begingroup$ Chimerism in humans is the result of two fertilized eggs merging (if and only if the two eggs would result in fraternal twins. Identical Twins do re-merge as well, but because they are genetically identical, they are not considered chimeras). If the two fathers fertilized the eggs, this could result in three parents, but this process has to occur early in the development of the egg in order to work. Chimerism wouldn't result in a baby that is not the mothers as her genetic contribution is present in both cells. Chimerism does rarely result in one of the few fertile intersex humans. $\endgroup$ – hszmv Jan 16 at 15:21
  • $\begingroup$ Correct. Chimeric birth process would not interfere with the maternity test involving a baby chimera, as all components of the chimera would be directly descended from the mother. But a female chimera could have a baby and the child would probably only be related to one of the parts of the mother. $\endgroup$ – James Ross Jan 18 at 10:45

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