Thursday, September 04, 2008

Are clones like cheap knockoffs?

The Science Not Fiction blog points out a scene in the recently-released post-apocalyptic movie Babylon A.D. where mercenary badass Toorop and his charges spot some tigers in a local marketplace:
Anyway, there’s the market place, there’s the tigers, there’s Aurora as Toorop and Sister Rebeka come up behind her. Toorop is not so impressed, later dismissing the beasts as “copies. Clones of clones. Fakes.”
But why so dismissive, Toorop? Cut them, and do they not bleed? Stick your hard-bitten, badass finger near the bars, and will you not bleed?
Of course you would. Cloned tigers are still tigers, after all, but for some reason, science fiction often depicts clones as somehow degraded from the original: The Michael Keaton film Multiplicity compares cloning to being photocopied, with each copy worse than the last, and Austin Powers’ spin on the concept is to render a Dr. Evil clone an eighth the size of the original.
That degradation of clones is actually a significant plot element in Kate Wilhelm's 1976 novel Where Late The Sweet Birds Sang. Humanity is nearly wiped out in an environmental catastrophe, and the only hope of human survival is a small well-supplied group of survivors who were able to collect the equipment and reagents needed to run a cloning operation. But there is a snag:
". . . the decline starts in the third clone generation, a decline of potency. He was breeding each clone generation sexually, testing the offspring for normalcy. The third clone generation had only twenty-five percent potency. the sexually reproduced offspring started with the same percentage , and, in fact, produced offspring, and then it started to climb back up and presumably would have reached normalcy again."

Walt was watching him closely, nodding now and then. David went on. "That was the clone-three strain. With the clone-four strain there was a drastic change. Some abnormalities were present, and life expectancy was down seventeen percent. The abnormals were all sterile. Potency was generally down to forty-eight percent. It was down-hill all the way with each sexually reproduced generation. By the fifth generation no offspring survived longer than an hour or two. So much for clone-four strain. Cloning the fours was worse. Clone-five strain had gross abnormalities, and they were all sterile. Life-expectancy figures were not completed. There was no clone-six strain. None survived."
I don't think it's too much of a spoiler to say that, while the characters overcome some of the technical difficulties of cloning to save the human race, ultimately it's individuals who are the product of sexual reproduction that re-inherit the Earth.

Wilhelm's characters cite the research of non-existent scientists Semple, Frerrer and Vlasic, but the fact is that at the time she wrote her novel the only animal that had been successfully cloned was the frog Xenopus laevis. I don't think it was particularly unreasonable for her to suppose that errors in DNA replication or other factors might cause clones to be somehow inferior to their parents, and, in fact scientists have found potentially damaging problems in cloned animals. The significance of some of those differences, such as shortened telomere length (usually a sign of aging), is unclear. I don't think it's unreasonable to believe that subsequent cloned generations might have compounded problems, a process called "replicative fading" (at least in the Star Trek universe).

However, since the 1970s cloning technology has improved significantly. The first mammalian clone created by nuclear transfer using embryonic cells as a source was reported by SM Willadsen in 1986. Ten years later Dolly the cloned sheep was created by nuclear transfer from an adult cell by Scottish scientists Keith Campbell and Ian Wilmut. And, more relevant to our discussion, scientists have begun to demonstrate that multiple generations of cloning is indeed a technical possibility. Some of the milestones:
So the good news is that it appears that if you can clone an animal, serial cloning is possible (even if less efficient). Of course it isn't ethical to perform similar cloning experiments aon humans, so it's unlikely we'll discover if the rule holds true for Homo sapiens any time in the near future. Hopefully the human race will never become so desperate that cloning technology is the only means for our survival.

Image: "Tiger Tiger Burning Bright" by digitalART2 on Flickr

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