Free Proteus in the Underworld by Charles Sheffield

yours. If we were identical twins we would share one hundred percent of our genetic material. If we were total strangers, unrelated in any way, we would share zero percent. From this lineage diagram you can determine for yourself our common genetic heritage."
    Sondra stared at the family tree. She shook her head. "I don't know how to do that."
    That earned another stare, this one more puzzled than knowing. "I am suitably appalled by your ignorance. But let me tell you how. Assuming there has been no inbreeding between distinct lines, the procedure is quite simple. Let's start with me. We go back through the tree, to every common ancestor that you and I share. Here we go." He stepped up through the generations. "Your great-great-grandfather was my great-grandfather, Dieter Wolf. He is our closest common ancestor. I was actually quite surprised to find that we share another, nine generations back, but that's so long ago I'm not sure I trust the results. Let's ignore it for the moment. We start with you. You share one hundred percent of genetic material with yourself. Now we go back toward our first common ancestor. At each generation, we multiply by one half. Your father was Soltan Dearborn. One half. His mother was Amelia Wolf. One quarter. Her mother was Cynthia Wolf-Stein. One eighth. And her father was Dieter Wolf. One sixteenth. You have one-sixteenth of Dieter Wolf's genetic material.
    "Now we come back down the tree. And at each generation, we multiply by one-half again. Dieter Wolf was my great-grandfather. Dieter Wolf's son was Seth Wolf. We're now at one thirty-second, a half of one-sixteenth. Seth Wolf's son was Hector Wolf. One sixty-fourth. And finally we get to me, because Hector Wolf was my father. One one-hundred-and-rwenty-eighth. You and I share less than one percent of our genetic material. If I throw in the other common ancestor, nine generations back, I simply add that to the other number. It makes hardly any difference—one part in five hundred thousand. Do you follow this?"
    Sondra was scowling. "I follow it, but I'm not sure I believe it. Or see why it's relevant."
    "Try it for some cases you know already. Brothers: two common ancestors—mother and father. Go back one generation from brother to mother, and down again from mother to other brother. That gives one quarter. Do the same for the father, another quarter. Add. Brothers share half their genetic material. Half-brothers share a quarter, cousins share one eighth. You and I share one one-hundred-and-twenty-eighth. Now come with me. I want to show you something."
    Bey was smiling to himself as he led the way out of the bedroom and descended two levels to the basement laboratory. Sondra followed, totally confused. Bey had a habit of subject change and digression unlike anything she had encountered in her studies or in the Office of Form Control. It sounded as if he were simply trying to annoy her, but she sensed that there was more to it than that.
    He was walking along past a set of closed metal doors with external cipher locks. At the fourth one he stopped, dialed in a combination, and swung it open.
    "Come in."
    Sondra followed and squeaked in alarm and surprise when a small brown figure jumped across the room and grabbed her by the hand.
    "Don't be scared. That's Jumping Jack Flash, and he's as friendly a chimp as you'll find anywhere."
    Sondra looked down and found herself staring into a pair of solemn and knowing brown eyes.
    "I just wanted to introduce the two of you," Bey went on. "And here's a question that I know you can answer, because it's in the standard form-control briefings. How much genetic material do a human and a chimpanzee have in common?"
    "Ninety-nine percent. Actually, a bit more than that."
    "Quite right." Bey reached down, and the chimp swung itself up his arm and to his shoulders in one easy movement. "That means you and I have less in common genetically than you and the chimp."
    "That's absolute nonsense!"
    "Of course it