"We can't be sure — the Core Wars and the Reformation haven't left us any records — but we do have some strong hypotheses, based on scaling laws and analogies with ourselves. Analogous anatomy was my principal subject as a student... Of course, that was a long time ago. They were much like us. Or rather, we were made in their image. But they were many times our size — about a hundred thousand times as tall, in fact. Because he was dominated by balances between different sets of physical forces, the average Ur-human was a meter tall, or more. And his body can't have been based, as ours is, on the tin-nucleus bond... Do you know what I'm talking about? The tin nuclei which make up our bodies contain fifty protons and one hundred and forty-four neutrons. That's twelve by twelve, you see. The neutrons are gathered in a spherical shape in symmetries of order three and four. Lots of symmetry, you see; lots of easy ways for nuclei to fit together by sharing neutrons, plenty of ways for chains and complex structures of nuclei to form. The tin-nucleus bond is the basis of all life here, including our own. But not the Ur-humans; the physics which dominated their structure — the densities and pressures we think they inhabited — wouldn't have allowed any nuclear bonding at all. But they must have had some equivalent of the tin bond..."

She held out her arms and wiggled her fingers. "So they were very strange. But they had arms, and legs, like us — so we believe, because otherwise why would they have given them to us?"

Dura shook her head. "That doesn't make any sense."

"Of course it does," Maxx smiled. "Oh, fingers have their uses. But haven't there been times when you'd have swapped your long, clumsy legs for an Air-pig's jetfart bladder? Or for a simple sheet of skin like a Surfer's board which would let you Wave across the Magfield ten, a hundred times as fast as you can now? You have to face it, my dear... We humans are a bad design for the environment of the Mantle. And the reason must be that we are scale models of the Ur-humans who built us. No doubt the Ur-human form was perfectly suited for whatever strange world they came from. But not here."

Dura's imagination, overheating, filled her mind with visions of huge, misty, godlike men, prising open the Crust and releasing handfuls of tiny artificial humans into the Mantle...

Deni Maxx looked deeply into Dura's eyecups. "Is that clear to you? I think it's important that you understand what's happened to your friend."

"Oh, it's clear," Adda called from his cocoon. "But it doesn't make a blind bit of difference, because there's nothing she can do about it." He laughed. "Nothing, now she's condemned me to this living hell. Is there, Dura?"

Dura's anger welled like Deni's heated superfluid. "I'm sick of your bitterness, old man."