Danchekker had reasoned that a violent mutation had taken place along the line of human descent isolated on Minerva. This latest piece of information pointed out the area in which the mutation had occurred; it didn’t attempt to explain why it had happened. But then, mutations are random events; there was nothing to suggest that there had been any specific cause to look for.
The evident fact of the emergence of Ganymean intelligence fitted in nicely with this body of theory too. The architecture of Minervan land dwellers had isolated the system that carried the toxins from the system that carried blood. Thus, when larger brains became in order, the way was clear to evolve a brain that could draw more blood without more toxins-the density of one network simply increased while that of the other didn’t. Higher brain functions could develop without hindrance. The intelligence of the Ganymeans was the natural and logical outcome of Miner-van evolution. Terrestrial evolution, however, pointed to no such natural and logical outcome; Man had somehow cheated the system.
“Well,” Hunt declared finally. “It’s interesting, sure. But what makes you say it shouldn’t have happened? Mutations are random events. The change came about as a mutation that took place on Minerva, somewhere along the line that led to the Lunarians and
from there to Man. It looks straightforward. What’s wrong with that?”
“I thought you’d say that,” ZORAC commented, somehow managing to give the impression of sounding quite pleased with itself. “That’s the obvious first reaction.”
“So-what’s wrong with it?”
“It couldn’t work. What you’re saying is that somewhere early on in the primate line on Minerva, a mutation must have occurred that deactivated the self-immunization system.”
“Yes,” Hunt agreed.
“But there’s a problem in that,” ZORAC advised him. “You see, I have performed extensive computations on further data available from 15-data that describe the genetic coding contained in vertebrate chromosomes. In all species, the coding that controls the development of the self-immunization process in the growing embryo contains the coding that enables the animal specifically to absorb excess carbon dioxide. In other words, if you deactivated the self-immunization mechanism, you’d also lose the ability to tolerate a C02-rich environment. . . .”
“And Minerva was becoming CO2-rich,” Hunt supplied, seeing the point.
“Exactly. If a mutation of the kind you’re suggesting occurred, then the species in which it had occurred could not have survived on Minerva. Hence, the ancestors of the Lunarians could not have mutated like that. If they did, they’d have died out. The Lunarians would never have existed and you wouldn’t exist.”
“But I do,” Hunt pointed out needlessly, but with a certain sense of satisfaction.
“I know, and you shouldn’t, and that’s my question,” ZORAC concluded.
Hunt stubbed out his cigarette and lapsed into thought again. “What about the funny enzyme that Chris Danchekker is always talking about? He found it in all the preserved Oligocene animals in the ship here, didn’t he? There were traces of a variant of it in Charlie too. D’you reckon that could have something to do with it? Maybe something in the environment on Minerva reacted in some complicated way and got around the problem and the enzyme appeared somehow in the process. That would explain why today’s terrestrial animals haven’t got it; the ancestors they’re descended from never went there. Perhaps that’s why modern Man
doesn’t have it either-he’s been back on Earth for a long time now and away from the environment that stimulated it. How about that?”
“Impossible to confirm,” ZORAC pronounced. “Inadequate data available on the enzyme at present. Very speculative. Also, there’s another point it doesn’t explain.”
“Oh, what?”
“The radioactive decay residues. Why should the enzymes found in the Oligocene animals appear to have been formed from radioisotopes while the ones found in Charlie didn’t?”
“I don’t know,” Hunt admitted. “That doesn’t make sense. Anyhow, I’m not a biologist. I’ll talk about all this to Chris later.” Then he changed the subject. “ZORAC-about all those equations you computed.”
“Yes?”
“Why did you compute them? I mean. . . do you just do things like that spontaneously. . . on your own initiative?”
“No. Shilohin and some of the other Ganymean scientists asked me to.”