“That enzyme was not a result of any natural process! It was something that had been manufactured and introduced artificially. That was where the radioactive decay products came from; the enzyme was manufactured artificially and included radioactive tracer elements to allow its progress through the body to be tracked and measured. We use the same technique widely in medical and physiological research ourselves.”
Hunt held up a hand to stop Danchekker going any further for the time being. He sat forward in his chair and closed his eyes for a second as he mentally stepped through the reasoning that the professor had summarized.
“Yes. . . okay. . . You’ve pointed out all along that chemical processes can’t distinguish a radioisotope from a normal one. So, how could the enzyme have selected radioisotopes to build into itself? Answer: It couldn’t; somebody must have selected them and therefore the enzyme must have been manufactured artificially. Why use radioisotopes? Answer: Tracers.” Hunt again looked across at the professor, who was following and nodding encouragement. “But the enzyme does a specialized job on the modified DNA chain, and you’ve already established that the DNA was modified artificially in the animals that were shipped to Minerva. . . . Ah, I see . . . I can see how the two tie in together. What you’re saying is that the Ganymeans altered the DNA coding of the terrestrial animals, and then manufactured a specific enzyme to operate on the altered DNA.”
“Exactly.”
“And what was the purpose of it all?” Hunt was becoming visibly excited. “Any ideas on that?”
“Yes,” Danchekker replied. “I think we have. In fact the things
that we have just considered tell us all that we need to know to guess at what they were up to.” He sat back and interlaced his fingers again. “With the enzyme performing in the way that I have just described, the object of the exercise becomes clear. At least I think it does. . . . If the animals that possessed the already altered DNA were implanted with the enzymes, the chromosomes in their reproductive cells would have been modified. This would have made it possible for a strain of offspring to be bred from them who possessed the CO2 coding in the form of an isolated, compact unit that could be manipulated and ‘got at’ with comparative ease. If you like, it enabled this particular characteristic to be separated out, perhaps with a view to its becoming the focal point of further experiments with later generations. . . .” Danchekker’s voice took on a curious note as he uttered the last few words, as if he were hinting that the main implication of his dissertation was about to emerge.
“I can see what you’re saying,” Hunt told him. “But not quite why. What were they up to then?”
“That was how they sought to solve their environmental problem after all else had failed,” Danchekker said. “It must have been something that was thought of during the later period of Ganymean history on Minerva-sometime after the Shapieron went to Iscaris, otherwise Shilohin and the others would have known about it.”
“What was how they sought to solve it? Sorry, Chris, I’m afraid I’m not with you all the way yet.”
“Let us recapitulate for a moment on their situation,” Danchekker suggested. “They knew that the CO2 level on Minerva had begun to rise, and that one day it would reach a point that they would be unable to withstand; the other Minervan native species would be unaffected, but the Ganymeans would be vulnerable as a consequence of their breeding their original tolerance out of themselves as part of the trade-off for better accident-resistance. They lost it when they took the decision to dispense permanently with their secondary circulation systems. They declined climatic engineering as a solution and tried migration to Earth and the Iscans experiment but both failed. Later on, it appears, they must have tried something else.”
Hunt was all ears. He made a gesture of total capitulation and said simply, “Go on.”
“One thing that they did discover on Earth, however, was a family of life that had evolved from origins in a warmer environment than that of Minerva, and which had not had to contend with the load-sharing problem that had caused the double-circulatory-system architecture to become standard on their own planet. Of particular interest, terrestrial life had evolved a completely different mechanism for dealing with carbon dioxide-one that did not depend on any secondary circulation system.”