Hacker News Reader

See Bateman's principle [1]. In most species, variability in reproductive success is greater in males than in females. This is also true for humans (even today) [2], modern human may have twice as many female ancestors as male ancestors.

This is fairly intuitive result when you consider gestation time - imagine a scenario where there are more male than female in a given moment for a given species. At most each female got fertilized once, so the number of distinct male parents is less than or equal to the number of females. If there are more females than males, the you get the same situation (less distinct male parents). This result is simply because a male parent can fertilize multiple females quickly, while gestation period limit the females.

This dynamic has led to sexual selection mostly affecting the males of the species, which means that this is where the competition happens. The move from polygamy to monogamy in human culture has allowed more males to reproduce and reduced this effect (although it still exists, and is significant).

1. https://en.wikipedia.org/wiki/Bateman%27s_principle

2. https://en.wikipedia.org/wiki/Reproductive_success#Humans

Can we look at species like Betta fish (I believe here the males do the hatching) to confirm such hypotheses?

For typical oviparous fish the cost and timing of reproduction is similar between males and females (dumping a large mass of sperm vs. dumping a large mass of eggs, then taking care of the children) and fancy reproductive organs are irrelevant technology.

Exactly, however, the parent post also tried to expand this to a more general concept of evolutionary pressure and competitive behavioural patterns as I understood. If that is true we can solve a lot of 'problems' in the world by simply having the men doing at least most of the child care for the first few month of a toddlers life to compensate for the for the month before.

Interestingly, there is this paragraph in the Wikipedia article:

> Although Bateman's principle served as a cornerstone for the study of sexual selection for many decades, it has recently been subject to criticism. Attempts to reproduce Bateman's experiments in 2012 and 2013 were unable to support his conclusions. Some scientists have criticized Bateman's experimental and statistical methods, or pointed out conflicting evidence, while others have defended the veracity of the principle and cited evidence in support of it.

Seems like a very convincing conjecture otherwise, though.

> modern human may have twice as many female ancestors as male ancestors.

I'm having trouble to understand how this can be true. It seems like every human should have equal numbers of male and female ancestors, e.g. by induction on how many generations back you look.

A single man can be your ancestor in more than one slot on your family tree.

Yes, but this is pretty severely understated. Everyone in your family tree definitely will appear there many times over, except for very recent ancestors.

Taking an average human generation time of 25 years, you would theoretically have 2^30 = roughly a billion ancestors 30 generations back, or 750 years ago. But the population of the Earth in 1300 was... maybe 400 million. (e.g. https://www.census.gov/data/tables/time-series/demo/internat... for world population estimates)

And your ancestors in 1300 aren't drawn from the entire population of the world; they're drawn from a tightly restricted subset of that.

And if you think that's ridiculous, imagine how many ancestors you'd have thirty-one generations back!

everyone has more single uncles than single aunts. Human history was not entirely monogamous, and a few number of men mated a larger number of women.

The main difference between male and female is cost of reproduction. Sperm is tiny and can be produced in massive quantities. Eggs are much larger and take more energy to produce. This difference is then carried into other parts of reproductive strategy. The two sexes reach a state of equilibrium with each other in terms of strategy.

Females are super careful about picking a mate because they spend months making an egg. They have a sunk cost. And females are relatively more caring about young because it is cheaper than making a new egg.

This access control forces males to evolve to be pleasing and provide some proof of quality. And this proof of quality can create more of a sunk cost for the male. They stick around and protect the young because it is easier to do that than find another female, impress them, build a nest etc.

Also, sex is very very obvious in terms of primary sexual characteristics. We have literally evolved to focus on those things. But outside of reproduction it is far less obvious in biology. On an individual level it is better to think of sex as an output rather than an input. Things don't happen because of the sex variables state, rather sexual characteristics are a consequence of other processes.

> Eggs are much larger and take more energy to produce.

>Females are super careful about picking a mate because they spend months making an egg.

The prevailing science was that females - assuming we are talking about humans - don’t make eggs rather are born with a finite number that reduces over their life time.

Only in the last couple years has the science begun to be questioned with the possibility that women do in fact make new eggs during adulthood. However, as far as I know that is still an open ended question being studied, whereas you offer some very specific facts about the required energy to produce eggs, which would suggest that in fact studies have not only confirmed women do actually make new eggs during their lifetime but there is further understanding about that process.

Could you link any studies about women producing new eggs “every couple months” and the energy required that you reference?

It is a higher cost regardless of when that cost is incurred. Although with humans I would guess that the 9 months of pregnancy and years of care is the relevant sunk cost. Compare that to the relative ease of a male who could have many offspring per year with little effort.

> Although with humans I would guess that the 9 months of pregnancy and years of care is the relevant sunk cost.

Humans are social animals with a wide variety of cultural values, in most cultures throughout history it won’t be a viable option for a man to go around impregnating multiple women every year and likely result in becoming a social outcast in civilized societies or outright killed in others.

Most cultures tend to be monogamous, courting and marriage being fairly common and also dowries were and are real thing -where a man pays a cost for each daughter to be married - not to mention co-evolution of societal norms that have also resulted in laws in some societies requiring child support until a child is 18. Whatever the natural biological costs, humans seem to have created different social norms and laws that have there own costs tending to curb the behavior you describe.

But that behaviour (monogamous, courting and marriage) can absolutely be seen as an evolutionary adaption. Male birds do not really need to help a female build a nest or look after eggs. But if they don't the female will deny access to sex, or the offspring will never hatch. And the female could just mate with any random bird, and not bother building a nest. But the egg won't survive.

The same is true of humans. If a males want their kids to survive to reproductive age then looking after their mum and the kids during infancy is the best strategy. And the best strategy for the mum is to use what power she has to encourage that. That may not be entirely a reflection of biology now, but it certainly was in the past. And it is no accident that humans find certain traits attractive in a mate.

But the difference in cost absolutely does still exist. Single parent households where the mum is left holding the baby are not exactly unusual. And the health burden of carrying a child and birthing is 100% on the women.

> Only in the last couple years has the science begun to be questioned with the possibility that women do in fact make new eggs during adulthood. However, as far as I know that is still an open ended question being studied,

Of all things we know and think we know, we still don't know this? That's a miracle.

I think they were referring to gestation, rather than the initial production of the ovule.

The cost of an egg is negligible compared to the cost of gestation, ie. bringing the embryo all the way to a baby.

Sexuality is a solution to Muller's ratchet [0].

[0] https://thehighbook.netlify.app/muller's-ratchet (first half)

The main point is selection at the level of individual sperm. Sperm are very cheap, but carrying an infant to term is very expensive. It is an absolute requirement to avoid carrying an infant with genetic disorders, to whatever extent possible. So the male creates a million sperm, and the female puts them through an obstacle course. A sperm with genetic defects probably won't even survive in the harsh environment, let alone win the race. So you're guaranteed that the winner of the Fallopian race is at least basically healthy, with basic functioning metabolic machinery and so on.

The metabolic machinery in the sperm is thrown away in favor of that in the egg, that's why mitochondrial RNA is matrilineal.

Even if it's thrown away there's still value in proving its function, as a proxy for general genetic fitness.

You are ascribing a utility optimisation to evolution that doesn't happen. There is an arms race happening on the selection because those who successfully procreate proliferate, and it can be difficult to undo changes. It doesn't matter if it's wasted energy or complications to have egg level defense mechanisms, if this trait evolved once because for whatever reason that selectivness was increasing chances of passing down those genes, absent négative sélection pressure and a viable genetic pathway out it's gonna stay there.

If there's a evo geneticist around, one thing I'm wondering is whether some of these traits might have evolved as a heck from the male side. E.g., if I have mutations that increase selectivness of the females against everyone but me, passing those mutations would bias later generations to select for my gene line. I'm not sure whether this is feasible or likely, but it's an example of evolutionary benefit without any real benefit if possible

"Parental investment theory, a term coined by Robert Trivers in 1972, predicts that the sex that invests more in its offspring will be more selective when choosing a mate, and the less-investing sex will have intra-sexual competition for access to mates. This theory has been influential in explaining sex differences in sexual selection and mate preferences, throughout the animal kingdom and in humans."

https://en.wikipedia.org/wiki/Parental_investment

I wonder if this changes with access to cheap, effective, and easy to use birth control (for both sexes), plus societal enforcement of males to participate sharing their resources to raising children, at least by garnishing wages.

I know many people, male and female, who would be considered prime mating material opting out of having children because they do not want to spend the resources they would have to to raise children.

I think it has to be all completely historical. In some species the male is the suitor, in others, the female is; and there are - or used to be, sadly - enough species for every linear combination of both possibilities.

If I know anything about nature, it's that it's a brute-force optimizer for biological fitness. Every possible combination of traits could feasibly be tested on these scales.

I don't think dzink's point relies on whether the suitor is male or female, but that the distinction exists at all and is so widespread.

> [...] and there are - or used to be, sadly - enough species for every linear combination of both possibilities.

Extinction is sad, but there's still plenty enough species to make this statement true.

> If I know anything about nature, it's that it's a brute-force optimizer for biological fitness. Every possible combination of traits could feasibly be tested on these scales.

Not quite. Eg there's basically no wheel in nature, despite the structure itself being quite simple. That's mostly because it's hard to evolve in small steps.

> there's basically no wheel in nature

Agreed, but V-ATPase is worth mentioning as it has a rotor and is very highly conserved. I guess it all depends on scale.

Yes. I was talking about a macroscopic wheel.

>male or female, but that the distinction exists at all and is so widespread.

Fair enough. I do find it interesting that even in plants that have N different sexes, their life cycles are still often dimorphic.

Maybe the most fundamental abstraction really is the difference between a 1 and a 0.

There is also the third gender in domesticated animals: human breeders. Humans breeders are curating the species and easing the growth of human-favored varieties. There is also the interesting consequences of that in human-disfavored species who evolve to survive in distributed ways despite, or even possibly using our intelligence and tactics in their favor (cockroaches, rodents, viruses, parasites, kudzu, you name it). Nature is a massive calculator, and its algorithms are so interesting, we’ve got to test more of them in computing.

Also have a look at rye and oats. They are both thought to be the result of Vavilovian mimicry.

> In plant biology, Vavilovian mimicry (also crop mimicry or weed mimicry[1][a]) is a form of mimicry in plants where a weed evolves to share one or more characteristics with a domesticated plant through generations of artificial selection.[2] It is named after Nikolai Vavilov, a prominent Russian plant geneticist.[2] Selection against the weed may occur by killing a young or adult weed, separating its seeds from those of the crop (winnowing), or both. This has been done manually since Neolithic times, and in more recent years by agricultural machinery.

> Vavilovian mimicry is a good illustration of unintentional selection by humans. Although the human selective agents might be conscious of their impact on the local weed gene pool, such effects go against the goals of those growing crops. Weeders do not want to select for weeds that are increasingly similar to the cultivated plant, yet the only other option is to let the weeds grow and compete with crops for sunlight and nutrients. Similar situations include antibiotic resistance and, also in agricultural crops, herbicide resistance. Having acquired many desirable qualities by being subjected to similar selective pressures, Vavilovian mimics may eventually be domesticated themselves. Vavilov called these weeds-become-crops secondary crops.

From https://en.wikipedia.org/wiki/Vavilovian_mimicry

>There is also the interesting consequences of that in human-disfavored species who evolve to survive in distributed ways despite, or even possibly using our intelligence and tactics in their favor (cockroaches, rodents, viruses, parasites, kudzu, you name it).

Nature and nurture. Gattica-level eugenics, at the end of the day, only affect the DNA. And eugenics will never save someone from the adage "Hard times make strong men. Strong men make good times. Good times make weak men. Weak men make hard times."

Not sure that adage is any true?

Eg western militaries don't seem to be worse at fighting than militaries from poor countries?

Are wheels useful without roads?

Agreed, wheels are less useful without roads. But there's some pretty flat natural territory out on earth, and some wheeled vehicles with rather good off-road capability.

> The males in many species compete to match some criteria of quality observed by females of that species.

It works in the other direction as well, especially if competition involves expending many resources on a single female. Only attractive females attract many competitors.

> It’s already applied in business [Founders (competing), investors (curating)] [...]

Wouldn't the even more basic dynamic in business been between company and customers? (And of course also between company and suppliers including workers who supply labour (or investors who supply capital, as you mention)?)

It's interesting that you bring up the egg. It reminds me of one day in my cell biology class in undergrad when we talked about why there are even eggs and sperm at all. I remember it only vaguely but I think maybe it was something about how small differences in motility and mitochondrial count between similarly shaped and sized cells would put selective pressure on them to differentiate. Maybe it's just a useless thing I don't really remember, but there's a part of my brain that wonders if it would yield some insight into what you're describing.

Sexual divergence is a game theoretical consequence of the differing costs two parents might have to form an offspring via sexual reproduction. Suppose a population of hermaphoditic sexually-reproducing species grows large enough to be comfortably self-sustaining and there is no difficulty in finding / exchanging gametes a sexual partner. At this point, every individual is equally capable of mothering or fathering the offspring, but one (say, mothering) ends up being more expensive because it requires more resource investment. Then a genetic quirk that causes a particular individual to preferentially spend more time fathering will be beneficial towards individual fitness, as the offspring/cost ratio is skewed in their favor. Eventually, one or more such genes catch on, and form the first steps of the evolution of the subpopulation with them into a male-type. And, over time, those better at specializing in being male-type will outcompete those who are less specialists at finding mothering partners, increasingly diverging this subpopulation towards maleness.

Now a population of mixed male-type and hermaphoditic-type individuals by definition can only skew male-type (in the sense that the average individual over the entire population somewhat prefers fathering over mothering). But each offspring has one male and one female parent; i.e. the population of parents does not skew in either direction. Run the math and you'll find that, counting hermaphodites as 1/2 in each category, there are more offspring per female-type than per male-type: those hermaphodites who prefer mothering are now the sexually fittest individuals in the group. And much like in the case with males above, a genetic preference towards mothering will catch on among the hermaphoditic population and begin skewing a subpopulation ever more female-like.

Eventually the male-type and female-type sexes fully diverge from each other, and the initial population of hermaphodites get out competed by the sexual specialists and fall solely into the fossil record.