Homosexuality and evolution

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For clarity's sake, I'm saying:

Sorry for all the posts.

Am I misunderstanding? Is the question more like "Why isn't homosexuality eliminated in, like, a generation being that same-sex couples can't reproduce?"

Ok model 2:

Model 1 assumed a very low reproduction rate that resulted in homosexuality being eliminated. I'm going to keep the same assumptions only make the reproduction rate of homosexuals to be 30% (so that their population actually increases)

Generation 0: 100 homosexuals, 900 heterosexuals

Generation 1: 120 homosexuals, 1440 heterosexuals

Generation 2: 144 homosexuals, 2304 heterosexuals ( I screwed up on this last post accidentally doubled it )

Generation 3: 173 homosexuals, 3686 heterosexuals

Now in this model homosexuals aren't dying out, but they are becoming a smaller and smaller proportion of the population. Let's calculate the percentage at each generation:

Generation 0: 10% homosexuals, 90% heterosexuals

Generation 1: 7.7% homosexuals, 92.3% heterosexuals

Generation 2: 5.6% homosexuals, 94.4% heterosexuals

Generation 3: 4.5 % homosexuals, 95.5% heterosexuals

As long as we remain in perpetual growth mode, the percentage of heterosexuals will increase over time eventually approaching 100%. The pure numbers of homosexuals increases, but this percentage change will become important in the next model.

Model 3:

Let's now assume a growth neutral population because we're in a time of hardship. Heterosexuals still reproduce at a rate of 80% and homosexuals reproduce at a rate of 30%, but now people die proportionally above over 1000 total.

Generation 0: 100 homosexuals, 900 heterosexuals

Generation 1: 120 homosexuals, 1440 heterosexuals (43 homosexuals die, 517 heterosexuals die)

Generation 1 (after mortality): 77 homosexuals, 923 heterosexuals

Generation 2: 92 homosexuals, 1477 heterosexuals (33 homosexuals die, 535 heterosexuals die)

Generation 2 (after mortality): 59 homosexuals, 942 heterosexuals

Under this growth neutral regime both the percentage and the total number of homosexuals will eventually decrease to 0. In the real world humanity has gone through both periods of hardship where growth was neutral or even negative, and periods of booming population growth. Under both regimes the percentage of a trait reducing reproductive success will reduce, but it these times of hardship that actually eliminate traits. Now homosexuality has not be eliminated, and I will present why in my follow-up carrier models. I need to take a break though.

Ok now for the next model. Up to this point we've assumed 100% inheritability. For this model I'm going to go back to the low reproduction rate of model 1 just to illustrate the point.

Model 4:

Homosexuals reproduce at a rate of 10%, heterosexuals reproduce at a rate of 80%. Homosexuals produce 2 homosexual children, and 2 children that are heterosexual but carry the homosexual trait. These children reproduce at the same rate as other heterosexuals. They produce 2 homosexuals and 2 carriers. For simplicity I will assume heterosexual carriers only reproduce with other heterosexual carriers, otherwise this gets very complicated.

Generation 0: 100 homosexuals, 900 heterosexuals, 0 carriers

Generation 1: 20 homosexuals, 1440 heterosexuals, 20 carriers

Generation 2: 20 homosexuals, 2304 heterosexuals, 20 carriers

Generation 3: 20 homosexuals, 3686 heterosexuals , 20 carriers

In this model the total population actually stabilizes after a generation. But again on percentage the ratio is decreasing and if we introduce mortality, both the carriers and the homosexuals will be eliminated. All of this can be fixed if we introduce a reproduction advantage to the carriers and set the rates of inheritance correctly.

Ok last one.

Model 5:

Instead of going through every combination I'm going to skip to the end for a full model since I have introduced all the individual elements previously. We will assume hardship (population stays at 1000 with equal mortality rate). Homosexuals reproduce at a rate of 30% and produce 50% homosexuals 50% carriers. Heterosexuals reproduce at 80% and produce 100% other heterosexuals. Heterosexual carriers reproduce at 100% and produce 90% other carriers, 10% homosexuals.

Generation 0: 100 homosexuals, 900 heterosexuals

Generation 1: 60 homosexuals, 1440 heterosexuals, 60 carriers (21 homosexuals die, 21 carriers die, 517 heterosexuals die)

Generation 1 after mortality: 39 homosexuals, 923 heterosexuals, 39 carriers

Generation 2: 30 homosexuals, 1477 heterosexuals, 93 carriers (11 homosexuals die, 553 heterosexuals die, 35 carriers die)

Generation 2 after mortality: 19 homosexuals, 924 heterosexuals, 58 carriers

Generation 3: 22 homosexuals, 1478 heterosexuals, 116 carriers (11 homosexuals die, 563 heterosexuals die, 44 carriers die)

Generation 3 after mortality: 11 homosexuals, 915 heterosexuals, 72 carriers

Generation 4: 21 homosexuals, 1464 heterosexuals, 130 carriers (8 homosexuals die, 555 heterosexuals die, 50 carriers die)

Generation 4 after mortality: 13 homosexuals, 909 heterosexuals, 80 carriers

Generation 5: 24 homosexuals, 1454 heterosexuals, 152 carriers (9 homosexuals die, 557 heterosexuals die, 59 carriers die)

Generation 5 after mortality: 15 homosexuals, 897 heterosexuals, 93 carriers

Let's check each by percentage:

Generation 0: 10% homosexual, 90% heterosexual, 0% carrier

Generation 1: 3.9% homosexual, 92.3% heterosexual, 3.9% carriers

Generation 2: 3% homosexual, 92.4% heterosexual, 5.8% carriers

Generation 3: 2.2% homosexual, 91.5% heterosexual, 7.2% carriers

Generation 4: 1.3% homosexual, 90.9% heterosexual, 8% carriers

Generation 5: 1.5% homosexual, 89.7% heterosexual, 9.3% carriers

Yes I'm aware they don't all add up to 100%. This is to due to rounding errors and having a whole number of people. The point is because of the evolutionary advantage of the carriers, they accumulate with each generation. Eventually the population of carriers are high such that the homosexual population is also increasing. If we extended this out for thousands of generations it would eventually become just carriers as the "pure heterosexuals" are eliminated by having a lower reproduction rate than the carriers. The homosexuals survive at a low level because the carriers produce them at a 10% rate.

The actual factors causing homosexuality are undoubtedly more complex than what I've presented here, but this is the evolutionary theory of why homosexual people still exist while likely having a lower biological reproduction rate than heterosexuals.

Bottom line: If we are correct in the assumption that homosexuality decreases your chances of reproducing, there must be a benefit to the traits that lead to homosexuality when present in heterosexual individuals such that "pure heterosexuality" has been eliminated by evolution.

Yes, I just called everyone a little bit gay

Within every population, there are variations. A blue-eyed population might have eye color that ranges from pale blue to deep-sea blue (assuming mixed-dominance for intensity). A "tall" population may have a range of adult heights from 5'8" to 6'8" (or more). A "hetero" population may range from strict heterosexual behavior to "bi-curious" or full bisexuality.

Sexuality is a spectrum of blended types from "Type A" to "Type Z" (and everything in between) and not only those two extremes.

THAT is what evolution accomplishes.

Assuming for discussion that homosexuality is genetically grounded we can still appreciate that many traits are polygenic/oligogenic (which I'll just call multigenic), involve the interactions of multiple genes, rather than monogenic. Assuming further that homosexuality is such a multigenic trait it wouldn't be necessary for there to be an advantage to the specific individuals carrying the confluence of genes so long as the population as a whole, which carries the collection of genes that can in some individuals coalesce to produce the trait, does not suffer a significant enough disadvantage to promote the elimination of the involved genes from the population.

Monogenic traits that confer reproductive disadvantage have a clear selection bias against them to various degrees, but multigenic traits are more complex as the fitness of those carrying the component genes but not the multigenic confluence thereof regulates the emergence of the trait as a recombinatoric inevitability.

The only thing that can be selected for or against are the individuals carrying the confluence that yields the trait, not the others carrying the individual component genes for whom those genes are inactive and don't contribute to their fitness either way, except for the metabolic energy requirements of duplicating the extra base pairs involved which is easily overshadowed by the metabolic cost of telomere duplication.

That is, unless some subsets of the genes involved in the multigenic trait engender their own traits that contribute their own effects, one way or another, to the fitness of the individuals carrying them. Otherwise only the proportion of the population carrying the trait seems to be regulated and seems to yield a normal distribution for the presence of the trait.

Actually, now that I think about it, I can only see how it would be an issue if the species were killing each other or somehow preventing each other from eating, so a higher population would be an advantage.