Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

B. Did ancient first-year students cast the same sort of spells, with the same power, as now? (Weak evidence for 1 over 2, but blood could also be losing powerful wizardry only.)

C. Additional test that distinguishes 1 and 2 using scientific knowledge of blood, will explain later.

"Okay," said Harry, "we can at least try to tell the difference between 1 and 2 and 3, so let's go with this right away, we can figure out more tests after we do the ones we already have. Now it's going to look a little odd if Draco Malfoy and Harry Potter go around asking questions together, so here's my idea. You'll go through Hogwarts and find old portraits and ask them about what spells they learned to cast during their first years. They're portraits so they won't know there's anything odd about Draco Malfoy doing that. I'll ask recent portraits and living people about spells we know but can't cast, no one will notice anything unusual if Harry Potter asks weird questions. And I'll have to do complicated research about forgotten spells, so I want you to be the one to gather the data I need for my own scientific question. It's a simple question and you should be able to find the answer by asking portraits. You might want to write this down, ready?"

Draco sat down again and scrabbled in his bookbag for parchment and quill. When it was laid down on the desk, Draco looked up, face determined. "Go ahead."

"Find portraits who knew a married Squib couple - don't make that face, Draco, it's important information. Just ask recent portraits who are Gryffindors or something. Find portraits who knew a married Squib couple well enough to know the names of all their children. Write down the name of each child and whether that child was a wizard, a Squib, or a Muggle. If they don't know whether the child was a Squib or a Muggle, write down 'non-wizard'. Write that down for every child the couple had, don't leave any out. If the portrait only knows the name of the wizarding children, not the names of all the children, then don't write down any data from that couple. It's very important that you only bring me data from someone who knows all the children a Squib couple had, well enough to know them all by name. Try to get at least forty names total, if you can, and if you have time for more, even better. Have you got all that?"

"Repeat it," Draco said, when he was done writing, and Harry repeated it.

"I've got it," Draco said, "but why -"

"It has to do with one of the secrets of blood that scientists already discovered. I'll explain when you get back. Let's split up and meet back here in an hour, 6:22pm that should be. Are we ready to go?"

Draco nodded decisively. It was all very rushed, but he'd long since been taught how to rush.

"Then go! " said Harry Potter and yanked off his cowled cloak and shoved it into his pouch, which began eating it, and, without even waiting for his pouch to finish, spun around and began striding rapidly toward the classroom door, bumping into a desk and almost falling over in his haste.

By the time Draco had managed to get his own cloak off and stow it in his bookbag, Harry Potter was gone.

Draco almost ran out the door.

"And then Janet was a Squib," said the portrait of a short young woman with a gold-trimmed hat.

Draco wrote it down. That was only twenty-eight but it was time to go back and meet Harry.

He'd needed to ask other portraits to help translating, English had changed a lot, but the oldest portraits had described first-year spells that sounded an awful lot like the ones they had now. Draco had recognized around half of them and the other half didn't sound any more powerful.

The sick feeling in his stomach had grown with each answer until finally, unable to take it any more, he'd gone off and asked other portraits Harry Potter's strange question about Squib marriages, instead. The first five portraits hadn't known anyone and finally he'd asked those portraits to ask their acquaintances to ask their acquaintances and so managed to find some people who'd actually admit to being friends with Squibs.

(The first-year Slytherin had explained he was working on an important project with a Ravenclaw and the Ravenclaw had told him they needed this information and then run off without saying why. This had garnered many sympathetic looks.)

Draco's feet were heavy as he walked through the corridors of Hogwarts. He should have been running but he couldn't seem to muster the energy. He kept on thinking that he didn't want to know about this, he didn't want to be involved in any of this, he didn't want this to be his responsibility, just let Harry Potter do it, if magic was fading let Harry Potter take care of it...

But Draco knew that wasn't right.

Chill the dungeons of Slytherin, gray the stone walls, Draco usually liked the atmosphere, but now it seemed too much like fading.

His hand on the doorknob, Harry Potter already inside and waiting, wearing his cowled cloak.

"The ancient first-year spells," Harry Potter said. "What did you find?"

"They're no more powerful than the spells we use now."

Harry Potter's fist struck a desk, hard. "Damn it. All right. My own experiment was a failure, Draco. There's something called the Interdict of Merlin -"

Draco hit himself on the forehead, realizing.

"- which stops anyone from getting knowledge of powerful spells out of books, even if you find and read a powerful wizard's notes they won't make sense to you, it has to go from one living mind to another. I couldn't find any powerful spells that we had the instructions for but couldn't cast. But if you can't get them out of old books, why would anyone bother passing them on by word of mouth after they stopped working? Did you get the data on the Squib couples?"

Draco started to hand the parchment over -

But Harry Potter held up a hand. "Law of science, Draco. First I tell you the theory and the prediction. Then you show me the data. That way you know I'm not just making up a theory to fit; you know that the theory actually predicted the data in advance. I have to explain this to you anyway, so I have to explain it before you show me the data. That's the rule. So put on your cloak and let's sit down."

Harry Potter sat down at a desk with torn scraps of paper arranged across its surface. Draco drew his cloak out of his bookbag, drew it on, and sat down across from Harry on the other side, giving the paper scraps a puzzled look. They were arranged in two rows and the rows were about twenty scraps long.

"The secret of blood," said Harry Potter, an intense look on his face, "is something called deoxyribonucleic acid. You don't say that name in front of anyone who's not a scientist. Deoxyribonucleic acid is the recipe that tells your body how to grow, two legs, two arms, short or tall, whether you have brown eyes or green. It's a material thing, you can see it if you have microscopes, which are like telescopes only they look at things that are very small instead of very far away. And that recipe has two copies of everything, always, in case one copy is broken. Imagine two long rows of pieces of paper. At each place in the row, there are two pieces of paper, and when you have children, your body selects one piece of paper at random from each place in the row, and the mother's body will do the same, and so the child also gets two pieces of paper at each place in the row. Two copies of everything, one from your mother, one from your father, and when you have children they get one piece of paper from you at random in each place."

As Harry spoke, his fingers ranged over the paired scraps of paper, pointing to one part of the pair when he said "from your mother", the other when he said "from your father". And as Harry talked about picking a piece of paper at random, his hand pulled a Knut out of his robes and flipped it; Harry looked at the coin, and then pointed to the top piece of paper. All without a pause in the speech.