Mutations of germline cells come with huge fitness penalties. Taking 0.01% of your genes introduces an extremely small amount of variance. And unilaterally replacing 50% of my genes with yours is equivalent to a 50% drop in fitness
99.9% of those genes will be identical, hence why I used the 0.01% number, if you want to induce more mutations you can (see bacteria) and if you want to introduce more mutations in a controlled way (i.e. not break anything important) you also can, and humans actually already do this, as do most multi-celular eukaryotes (see B cell selection in response to antigens, for example)
The bacterial method itself also doesn't seem to work in humans (because you need to have the genes during development, and less importantly you need to spread them throughout your body). So it seems to me like sex adds very significant benefits over these alternatives.
I'm not sure if it works in humans, but humans did not invent sex. Simple multi-ceulular eukaryotes did. In those species HGT works just fine and is indeed a contributor to evolutionary variance that got them to where they are. I had a great paper on this but can't find it, see for example: https://onlinelibrary.wiley.com/doi/pdf/10.1002/bies.201300007
It's not a big thing in practice, because sex works better, so it makes sense to protect against HGT in all but a few niche cases (transfer from bacteria-like organels such as mitochondria)
Is your view here coming from some quantitative estimate or further reasoning you didn't include in the comment, or is it reflecting the consensus view in some field? In either case, it would be great to see a pointer. If this is just your guess based on the reasoning in the comment, that's fine and I'm happy to leave the argument here (or with your rebuttal).
It reflects a consensus view in the field in so far as nobody has tried to justify sex in terms of variance in genetics since the 70s (see the very wikipedia article cited) and even that tried to justify it was being variance under very specific conditions that allow it to be less dangerous and/or with a higher chance of varying in a "right" direction.
Variance is for sure an advantage. But it's not the advantage. Since there are 1001 ways you can introduce variance.
So both under common sense and under all accepted models I know of the intuition presented here is wrong.
And you don't need much to figure that out, again, just try to answer the question:
If variance is the main reason we have sexed reproduction than why not do it bacteria-style, or more realistically why not do it B-cell-selection style but for germinal cells?
That also means the variance could be better controlled by environment, you could literally say "I want exactly x% variance".
Additional questions to ponder might be:
Those will also point you in the right direction of actually figuring out why we have sexed reproduction.
Again, this is not to say variance is not a benefit. Much like "locomotion over flat ground" is a benefit of crab legs. But "variance" is something boring that can come about 1000 different ways. The reason crab legs are interesting and special and worth evolving is showcased when looking at how crabs move on steep terrian. Similarly, the reason sexed reproduction is interesting and special and worth evolving only becomes obvious when thinking of things that you can only accomplish using it (or at least that are much more costly to accomplish otherwise, and that no other lifeforms do in other ways)
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If the above doesn't make sense please tell me and I'll try to rephrase
If you want a good pop-science book that goes over how biologists think of the role of sexed reproduction you could check out "The Red Queen: Sex and the Evolution of Human Nature". I read it like 4 years ago, when I knew nothing on the subject, and while in hindsight it has some bad points (and I don't agree with the central hypothesis) it does a good job of showcasing the different views in the field in a way that you can get with limited knowledge of the molecular level processes involved.
Automatically crossposted from https://sideways-view.com
From the perspective of an organism trying to propagate its genes, sex is like a trade: I’ll put half of your DNA in my offspring if you put half of my DNA in yours. I still pass one copy of my genes onto the next generation per unit of investment in children, so it’s a fair deal. And it doesn’t impact the average fitness of my kids very much, since on average my partner’s genes will be about as good as mine. (ETA: but see the discussion below, in which case the costs might be much bigger.)
But the trade has transaction costs, so I’m only going to do it if I get some benefit. In this post I’ll tell a particularly simple story about the benefit of sex. I think this is basically equivalent to the standard story, but I find it much clearer. It also makes it more obvious that we don’t require group selection, and that the benefit is very large.
Why doesn’t sex change the average fitness of my kids? The possibility of a “lucky” kid who gets the better genes from both of us is offset by the possibility of an unlucky kid who gets the worse genes from both of us. If the effects of genes are linear, the average fitness will be exactly the same as the parents. In practice I expect it to be slightly lower because of convexity and linkage disequilibrium.
But sex increases the average fitness of my grandchildren, because my fittest children will be responsible for a disproportionate fraction of my grandkids. More precisely, if my if an organism with fitness dX has (1+dX) kids per generation, then the total fitness of my grandkids is E[(1 + dX)^2] = 1 + 2 E[dX] + E[dX^2]. So increasing variance by 1 unit is as good as increasing average fitness by 0.5 units.
Reproductive decisions are naturally a tradeoff between average fitness and variance. Sex slightly lowers the average but increases the variance. If you try to get the same amount of variance with random mutations, you’ll have to totally tank your kid’s expected fitness, because your current genome is well-optimized, and you’ll also pass on fewer genes to the next generation (since some of yours got destroyed). In fact, it’s hard to think of any way to get similar benefits without exchanging genes.
Variance becomes linearly more important over time. For the fitness of my grandkids, 1 unit of variance is worth 0.5 units of fitness; for great-grandkids, they are equally valuable; for great-great-great-grandkids variance is twice as valuable. I don’t think we have to look too many generations ahead before the variance bonus from sex outweighs the costs. For example, if genetic fitness differs by 5% between my offspring, and sex reduces fitness by 1%, then sex breaks even within 6 generations.