I asked Nick if an analogy to Github repos would help illustrate the advantages of sexual recombination over asexual cloning or lateral gene transfer. Recombination is like a normal pull request - you have an organized diff at the same site as the previous functionality, and then you merge... back if maintainer evaluates the new code to be better (analogy is imperfect, but this is like evolution driving that allele into fixation if it confers advantage). Asexual reproduction is if you just forked the repo millions of times, making random char changes. And even if a couple of these forks end up accidentally producing an improvement, there’s no way for them to merge back into "master". Without recombination, you don't have systematic pooling of the genes. So you can either be on the lineage with beneficial mutation A or beneficial mutation B, not both. This is known as clonal interference. I thought the problem with horizontal gene transfer in bacteria is that it's not like an organized diff. It's like if you just took a random 500 line snippet and shoved it in some totally different repo in totally random place. But actually Nick corrected me on this point of the analogy. The problem with lateral gene transfer is not that you don't have an organized diff - the problem is LGT is that its not scalable to eukaryotes' large genomes (1000x larger than bacteria). You can't systematically exchange tens of thousands of genes (in order to drive up the variance evolution relies upon) through LGT, but you can through recombination. This kind of systematic parallel search across the genome became necessary once the genome size exploded after the endosymbiosis of the ancestral mitochondria (which kept shoving a bunch of its genes into the host cell’s DNA).show more

Dwarkesh Patel

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