Harry Potter And The Methods Of Rationality

Chapter 25: Hold off on Proposing Solutions

(The sun shone brilliantly into the Great Hall from the enchanted sky-ceiling above, illuminating the students as though they sat beneath the naked sky, gleaming from their plates and bowls, as, refreshed by a night's sleep, they inhaled breakfast in preparation for whatever plans they'd made for their Sunday.)

So. There was only one thing that made you a wizard.

That wasn't surprising, when you thought about it. What DNA mostly did was tell ribosomes how to chain amino acids together into proteins. Conventional physics seemed quite capable of describing amino acids, and no matter how many amino acids you chained together, conventional physics said you would never, ever get magic out of it.

And yet magic seemed to be hereditary, following DNA.

Then that probably wasn't because the DNA was chaining together nonmagical amino acids into magical proteins.

Rather the key DNA sequence did not, of itself, give you your magic at all.

Magic came from somewhere else.

(At the Ravenclaw table there was one boy who was staring off into space, as his right hand automatically spooned some unimportant food into his mouth from whatever was in front of him. You probably could have substituted a pile of dirt and he wouldn't have noticed.)

And for some reason the Source of Magic was paying attention to a particular DNA marker among individuals who were ordinary ape-descended humans in every other way.

(Actually there were quite a lot of boys and girls staring off into space. It was the Ravenclaw table, after all.)

There were other lines of logic leading to the same conclusion. Complex machinery was always universal within a sexually reproducing species. If gene B relied on gene A, then A had to be useful on its own, and rise to near-universality in the gene pool on its own, before B would be useful often enough to confer a fitness advantage. Then once B was universal you would get a variant A* that relied on B, and then C that relied on A* and B, then B* that relied on C, until the whole machine would fall apart if you removed a single piece. But it all had to happen incrementally - evolution never looked ahead, evolution would never start promoting B in preparation for A becoming universal later. Evolution was the simple historical fact that, whichever organisms did in fact have the most children, their genes would in fact be more frequent in the next generation. So each piece of a complex machine had to become nearly universal before other pieces in the machine would evolve to depend on its presence.

So complex, interdependent machinery, the powerful sophisticated protein machines that drove life, was always universal within a sexually reproducing species - except for a small handful of non-interdependent variants that were being selected on at any given time, as further complexity was slowly laid down. It was why all human beings had the same underlying brain design, the same emotions, the same facial expressions wired up to those emotions; those adaptations were complex, so they had to be universal.

If magic had been like that, a big complex adaptation with lots of necessary genes, then a wizard mating with a Muggle would have resulted in a child with only half those parts and half the machine wouldn't do much. And so there would have been no Muggleborns, ever. Even if all the pieces had individually gotten into the Muggle gene pool, they'd never reassemble all in one place to form a wizard.