Here’s the argument I’d give for this kind of bottleneck. I haven’t studied evolutionary genetics; maybe I’m thinking about it all wrong.
In the steady state, an average individual has n children in their life, and just one of those n makes it to the next generation. (Crediting a child 1⁄2 to each parent.) This gives log2(n) bits of error-correcting signal to prune deleterious mutations. If the genome length times the functional bits per base pair times the mutation rate is greater than that log2(n), then you’re losing functionality with every generation.
One way for a beneficial new mutation to get out of this bind is by reducing the mutation rate. Another is refactoring the same functionality into fewer bits, freeing up bits for something new. But generically a fitness advantage doesn’t seem to affect the argument that the signal from purifying selection gets shared by the whole genome.
Here’s the argument I’d give for this kind of bottleneck. I haven’t studied evolutionary genetics; maybe I’m thinking about it all wrong.
In the steady state, an average individual has n children in their life, and just one of those n makes it to the next generation. (Crediting a child 1⁄2 to each parent.) This gives log2(n) bits of error-correcting signal to prune deleterious mutations. If the genome length times the functional bits per base pair times the mutation rate is greater than that log2(n), then you’re losing functionality with every generation.
One way for a beneficial new mutation to get out of this bind is by reducing the mutation rate. Another is refactoring the same functionality into fewer bits, freeing up bits for something new. But generically a fitness advantage doesn’t seem to affect the argument that the signal from purifying selection gets shared by the whole genome.