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On the earth today most animals use a two sex mating system where male and female provide the same amount of genetics to the resulting offspring, despite the fact that in many cases the female provides a disproportionately high degree of resources in producing and raising the young than the 'free-loading' male.

However, this isn't always the case. Some ants, and other insects, depend on a haplodiploidy mating system where a mother may pass on 2/3 of her genetics to her (female) offspring. There are other unusual mating systems hybridogenesis where a female may always clone part of her own genetics.

In a way these systems seem to make more 'evolutionary sense'. If a mother is going to contribute the majority of effort into raising the offspring she would have incentive to ensure that the child has more of her genetics, and a male that provides only 1/3 of his genes to a female can still be a viable means of passing on his genetics so long as he gets to mate with more than one female at a time. While a mother would want some degree of genes from a male to gain the advantages of sexual reproduction (resistance to disease, higher degree of adaptability to unusual circumstances, ability to pass on advantageous mutations to the species as a whole etc), she could theoretically gain most of these benefits even if her child only inherited 1/3 or even 1/4 of their genes from her partner. Her children would suffer slightly in adaptability in this situation, but the ability to pass on significantly more of her genes per child could easily be enough of a boon to be worth trading away a bit of survivability/adaptability per child due to the lowered genetic variety.

Is there a reason this system would not work for other species, and in particular for sapient species? Can I justify the evolution of a sapient alien species, preferably somewhat mammal-like if possible, where the mother passed on the majority of her genetics to a child while keeping a smaller percentage of genes (I'd guess 1/3 or 1/4 would be the most likely combinations) from her mate? I'm looking for highly social species, but not euro-social; that is to say one matriarch does not produce most of the children, and all individuals are generally competing for mating rights with each other as seen in most mammal herding species.

Assuming this is possible how would the differences in genetic contribution affect the standard evolutionary roles of the species? For instance males would presumably be less likely to contribute in the care-giving of the young now that each young has less of it's own genetics. Would males be born less often in such a species, defying the traditional fisher principle? would males on such a gambit still compete for female matings, and thus evolve to (on average) be larger and stronger to engage in competition with other males?

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    $\begingroup$ In general, sexual reproduction is beneficial as a method of maximising genetic diversity in offspring. It is actually detrimental to the goal to produce offspring with less than half of their genes from either parent. $\endgroup$
    – Arkenstein XII
    Sep 4, 2019 at 23:48
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    $\begingroup$ Humans already have more DNA from mom than from dad, though it's a small difference. 1) Mitochondrial DNA only comes from the mother. 2) Females always pass down an X chromosome for #23 and males can pass down either a same-size X (to girls) or a smaller Y (to boys). I know I'm being pedantic, but how else am I supposed to have any fun? :-) $\endgroup$
    – Cyn
    Sep 5, 2019 at 0:13
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    $\begingroup$ Haplodiploid insects pass half of their own genes to each female offspring, not ¾. $\endgroup$
    – The Square-Cube Law
    Sep 5, 2019 at 4:10
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    $\begingroup$ They say the arc of history bends towards fairness, but that is only because our primate brains encompass the concept of justice. Mother Nature she plays by other rules and isn’t bound by context defined terms like fairness. $\endgroup$
    – EDL
    Sep 5, 2019 at 4:56
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    $\begingroup$ @ArkensteinXII genetic diversity is useful, but not necessarily enough to counter spreading more of your genes. That fact that we have so many known examples of formerly sexual creatures reverting to parthenogenesis shows that increase spread of genetics can trump genetic diversity in the short term. In the long term clonal species survival is lower due to lack of adaptation, but I feel a father providing 1/3 to 1/4 of their genetics is still enough gene flow to keep a reasonable evolutionary landscape for adaptability and passing of beneficial mutations for long term species survivability. $\endgroup$
    – dsollen
    Sep 5, 2019 at 13:51

3 Answers 3

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In regards as to why this may not work for other species: One problem is that males and females will need vastly different meiosis processes. In humans, egg and sperm cells are obviously different, but the processes that format the DNA for those gametes are pretty similar.

How does this evolve? How does the first female whose gametes have 2/3 of a full DNA complement find a male with 1/3 of a full DNA compliment? It seems exceedingly unlikely one female member of the species will have the right mutation(s) at the same time and in the same vicinity as a male with the right mutation(s).

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    $\begingroup$ This is not necessarily the case. If a cell of one of these organisms contains equal amounts of nuclear and extra-nuclear DNA, and the male gamete only transmits half of the father's nuclear DNA, the final ratio would be 3:1 in favour of the mother. Tweaking the amount of maternally inherited extra-nuclear DNA could provide whatever ratio is desired. $\endgroup$
    – Arkenstein XII
    Sep 5, 2019 at 3:19
  • $\begingroup$ There are a number of species out there that mate with a male but then 'throw out' part or all of his DNA, leading to clonal, half-clonal or more complex arragements. Given that fact isn't is possible to evolve a situation where both male and female provide the same mount of DNA, but the female 'ignores' much of the male DNA? $\endgroup$
    – dsollen
    Apr 21, 2020 at 1:24
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The whole purpose of sex, according to science, is to randomize the gene pool on each generation and keep things fresh and diverse. If you just keep all the same genes in every generation, then the whole population may succumb due to something targeting specifically those genes. Case in point: banana blight.

If you wish to see what happens when a child has a lot more genes from either parent... Do it like Oedipus and Paltith did. Half of your resulting siblings will be almost clones of your common parent. This never ends well.

In communities with a lot of inbreeding, a parent might not always pass more than about 50% of their genes to each offspring, but the offspring of their offspring may have more of that initial parent's genes more often. In the end it's the same as the previous paragraph but with a smaller ratio of children that can be sold to circuses.

In haplodiploid species this is not an issue because, as the wiki you linked to says, any recessive gene that might be lethal or deleterious ends up killing or handicapping the haploid males, so those genes are much harder to pass on. If a haploid male makes it to breeding age it is much more likely to carry no genes linked to diseases.

Just to be pedant: human females do pass more genes to their offspring than males. Humans have 47 chromosomes, not 46. People who insist we have only 46 hold a strong prejudice against mitochondria. The little [redacted]s spend day and night making ATP for us and we forget that they, too, have a chromosome.

Turns out that in humans, no mitochondria in sperm ever make it into the egg. All the mitochondria you have in you were passed by your biological mother. This is not necessarily true for other species, though.

In cis women/trans men, this already gives a little edge to the amount of genes inherited from the female side. For cis men/trans women, though, the ratio of female-inherited genes is higher because the Y chromosome is smaller and has less genes than the X.

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    $\begingroup$ There's also the whole Y vs. X chromosome thing, which constitutes a much larger difference in genetic material than mitochondrial DNA does. $\endgroup$
    – Logan R. Kearsley
    Sep 6, 2019 at 2:01
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The amount of genetic material contributed by each parent is constantly in flux.

The big problem you have is the male genome, These kinds of things try to evolve all the time, but of course any male genome that evolves a counter has a HUGE advantage. so it gets selected for until the ratio is stable again, or it pushes the other way and then female genomes that counter it are selected for. There is actually evidence that this kind of competition happens all the time. Both male and female genomes "want" to contribute more to their offspring. roughly 50/50 is just one of the stable outcomes of that competition, there are others.

Haplodiploidy encourages eusocial behavior, not the other way around. daughters are so much more closely related two sisters are actually more closely related to each other than their own offspring. So if favor much of the same cooperation having identical genomes favor in the the individual cells of your body, an individual unit is better off contributing to the whole than trying to strike out on its own. Whether males will contribute parental care is controlled by a number of factors the genomic contribution ratio is not enough by itself, so it is up to you if they contribute.

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  • $\begingroup$ I'm not sure your link proves your first case. That link is about DNA that is parental or maternal antagonistic, IE the gene is useful for one sex but harmful for another. It's not about increasing the amount of genes shared, only rather the existing gene's mutation is beneficial or harmful for a given sex, unless I missed something in my scanning of the document. $\endgroup$
    – dsollen
    Apr 21, 2020 at 1:28
  • $\begingroup$ Some of the genes mentioned are genes that alter how much of their associated genome gets passed on, several are sex specific. $\endgroup$
    – John
    Apr 21, 2020 at 2:43

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