Donald Moffitt - Genesis 01

long, crosslinks tend to form over a period of time. The tissue hardens, loses its elasticity. For a long time, Original Man thought collagen was the key to aging, simply because the effects of crosslinking were so pervasive. Wrinkles, stiff joints, slipped disks, degenerative circulatory conditions, arthritis—the lot! He worked on it for centuries and gave us the results. Now we know how to dissolve the crosslinks, and that’s why, when you’re about a third as old as I am, you’ll start to go in once or twice a year for your rejuvenation treatments.” He chortled at Bram. “I passed my sevenscore and ten a long time ago—I won’t say how long, but I’m a lot closer to two hundred than I am to one hundred and fifty, and with any luck I’ll get there! And I’ll tell you this. I look a lot better and feel a lot better than youngsters of ninety did back in the days when Original Man was at the mercy of nature.”
    “But,” Bram prompted delicately, “the human life span still is limited. Even with rejuvenation treatments.”
    “Yes, yes,” Doc Pol said vaguely. “What was I saying? Ah! The accumulation of errors. If collagen is subject to crosslinking, so must other long molecules be. Like DNA. You’re a genetic engineer. You can imagine what that does.”
    “Codons attached at the wrong sites! Inappropriate palindromes! Loops and detours! Wrong enzymes being made, or enzymes not being made at all! That must be it! Suppose you could find some way to tell those codons that they’ve grabbed a wrong place on a strand—get them to let go and cast about till they hook into an appropriate site? Like what you do in genetic engineering when you fool a stretch of nucleotide into accepting a foreign plasmid. Only in reverse! Dissolve a bond to undo the damage!”
    “‘Fraid not, son. Crosslinked DNA is part of the explanation, maybe, but it’s not the whole story.”
    Bram exhaled. “What, then?”
    “You know that DNA has a great capacity to repair itself.”
    “Yes, otherwise the stray damage caused by ionizing radiation would begin to add up in a long-lived species …” He looked at Doc with new surmise. “Accumulated errors!”
    “The ability of DNA to repair itself decreases with each cell generation. By the fiftieth generation it’s about gone. You know how redundant DNA is.”
    “Yes. A given cell uses less than one percent of the information in its DNA during its lifetime.”
    “Consider the redundant genes to be replacement parts. If a functional gene is damaged, a spare takes over its job. Over a period of time, all the spares are finally used up.”
    Bram’s face fell. “That would mean there’s no hope of reversing the aging process.”
    “There’s one more theory.”
    “Which is?”
    Doc Pol raised a sere hand and held it in front of his face as if studying it. After a bit, he put it back in his lap. “That our cells contain aging genes, just as they contain genes that mediate the various stages of embryonic and adolescent development. A sort of death switch, if you will. These switches tell the cell when the show’s over and it’s time to shut down. And there’s no cure for that, either, son. It would mean that the sequential shutdowns of age and death are just part of the normal biological process, like the genetic programming that shuts down various stages of embryonic development when the time comes. I’m told there was once a creature, called the salmon, that aged and died after spawning, but we’ve got an example closer to home—the Nar.” He shook his head. “No, my boy, if you’re looking for eternal life you’d have to imagine something that stops an inherent developmental process and keeps particular genes that are a part of our genetic material from expressing themselves.”
    “Like the dragonfly does,” Bram said, half to himself.
    “What’s that, my boy?”
    “Nothing,” Bram said quickly. “I was thinking about heterochronic eggs. The Nar interfered with normal embryonic development there and came up with a single giant cell that absorbs nourishment through an outer membrane and divides when it gets big enough.”
    Doc Pol looked at him shrewdly. “And you think genetic tinkering might some day interfere with death genes? That day’s a long way off, my young friend. Original Man never managed the trick, even at the top of his form, and we’re very small potatoes compared to him. And the Nar, even though they use something corresponding to