The Gentle Giants of Ganymede

looked inquiringly from side to side, at the same time turning up his hands. 'I guess I don #146;t really see the problem,' he confessed candidly. 'This enzyme existed in animal species from twenty-five million years back #151;right?'

'You #146;ve got it,' Sandy Holmes confirmed from across the table with a slight nod of her head.

'So in twenty-five million years they mutated out of all recognition. Everything changes over a period of time and it #146;s no different with enzymes. Descendant strains from this one are probably still around but they don #146;t look the same. . . .' He caught the expression on Danchekker #146;s face. 'No? . . . What #146;s the problem?'

The professor sighed a sigh of infinite patience. 'We #146;ve been through all that, Paul,' he said. 'At least, I was under the impression that we had. Let me recapitulate: Enzymology has made tremendous advances over the last few decades. Just about every type has been classified and catalogued, but never anything like this one, which is completely different from anything we #146;ve ever seen.'

'I don #146;t want to sound argumentative, but is that really true?' Carpenter protested. 'I mean . . . we #146;ve seen new additions to the catalogues even in the last year or two, haven #146;t we? There was Schnelder and Grossmann at Sгo Paulo with the P273B series and its derivatives. . . Braddock in England with #151;'

'Ah, but you #146;re missing the whole point,' Danchekker interrupted. 'Those were new strains, true, but they fell neatly into the known standard families. They exhibited characteristics that place them firmly and definitely within known related groups.' He gestured again toward the screen. 'That one doesn #146;t. It #146;s completely new. To me it suggests a whole new class of its own #151;a class that contains just one member. Nothing yet identified in the metabolism of any form of life as we know it has ever done that before.' Danchekker swept his eyes around the small circle of faces.

'Every species of animal life that we know belongs to a known family group and has related species and ancestors that we can identify. At the microscopic level the same thing applies. All our previous experiences tell us that even if this enzyme does date from twenty-five million years back, we ought to be able to recognize its family characteristics and relate it to known enzyme strains that exist today. However, we cannot. To me this indicates something very unusual.'

Wolfgang Fichter, one of Danchekker #146;s senior biologists, rubbed his chin and stared dubiously at the screen. 'I agree that it is highly improbable, Chris,' he said. 'But can you really be so sure that it is impossible? After all, over twenty-five million years? . . . Environmental factors may have changed and caused the enzyme to mutate into something unrecognizable. I don #146;t know, some change in diet maybe . . . something like that.'

Danchekker shook his head decisively. 'No. I say it #146;s impossible.' He raised his hands and proceeded to count points off on his fingers. 'One #151;even if it did mutate, we #146;d still be able to identify its basic family architecture in the same way we can identify the fundamental properties of, say, any vertebrate. We can #146;t.

'Two #151;if it occurred only in one species of Oligocene animal, then I would be prepared to concede that perhaps the enzyme we see here had mutated and given rise to many strains that we find in the world today #151;in other words this strain represents an ancestral form common to a whole modern family. If such were the case, then perhaps I #146;d agree that a mutation could have occurred that was so severe that the relationship between the ancestral strain and its descendants has been obscured. But that is not the case. This same enzyme is found in many different and nonrelated Oligocene species. For your suggestion to apply, the same improbable process would have had to occur many times over, independently, and all at the same time. I say that #146;s impossible.'

'But. . .' Carpenter began, but Danchekker pressed on.

'Three #151;none of today #146;s animals possesses such an enzyme in its microchemistry yet they all manage perfectly well without it. Many of them are direct descendants of Oligocene types from the Ganymean ship. Now some of those chains of descent have involved rapid mutation and adaptation to meet changing diets and environments while others have not. In several cases the evolution from Oligocene ancestors to today #146;s forms has been very slow and has produced only a small degree of change. We have made detailed comparisons between the microchemical processes of such ancestral Oligocene ancestors recovered from the ship and known data relating to animals that exist today and are descended from those same ancestors. The results have been very much as we expected #151;no great changes and clearly identifiable relationships between one group and the other. Every function that appeared in the microchemistry of the ancestor could be easily recognized, sometimes with slight modifications, in the descendants.' Danchekker shot a quick glance at Fichter. 'Twenty-five million years isn #146;t really so long on an evolutionary time scale.'

When no one seemed ready to object, Danchekker forged ahead. 'But in every case there was one exception #151;this enzyme. Everything tells us that if this enzyme were present in the ancestor, then it, or something very like it, should be readily observable in the descendants. Yet in every case the results have been negative. I say that cannot happen, and yet it has happened.'

A brief silence descended while the group digested Danchekker #146;s words. At length Sandy Holmes ventured a thought. 'Couldn #146;t it still be a radical mutation, but the other way around?'

Danchekker frowned at her.

'How do you mean, the other way around?' asked Henri Rousson, another senior biologist, seated next to Carpenter.

'Well,' she replied, 'all the animals on the ship had been to Minerva, hadn #146;t they? Most likely they were born there from ancestors the Ganymeans had transported from Earth. Couldn #146;t something in the Minervan environment have caused a mutation that resulted in this enzyme? At least that would explain why none of today #146;s terrestrial animals have it. They #146;ve never been to Minerva and neither have any of the ancestors they #146;ve descended from.'

'Same problem,' Fichter muttered, shaking his head.

'What problem?' she asked.

'The fact that the same enzyme was found in many different and nonrelated Oligocene species,' Danchekker said. 'Yes, I #146;ll grant that differences in the Minervan environment could mutate some strain of enzyme brought in from Earth into something like that.' He pointed at the screen again. 'But many different species were brought in from Earth #151;different species each with its own characteristic metabolism and particular groups of enzyme strains. Now suppose that something in the Minervan environment caused those enzymes #151;different enzymes #151;to mutate. Are you seriously suggesting that they would all mutate independently into the same end-product?' He waited for a second. 'Because that is exactly the situation that confronts us. The Ganymean ship contained many preserved specimens of different species, but every one of those species possessed precisely the same enzyme. Now do you want to reconsider your suggestion?'

The woman looked helplessly at the table for a second, then made a gesture of resignation. 'Okay. . . If you put it like that, I guess it doesn #146;t make sense.'

'Thank you,' Danchekker acknowledged stonily.

Henri Rousson leaned forward and poured himself a glass of water from the pitcher standing in the center of the table. He took a long drink while the others continued to stare thoughtfully through the walls or at the ceiling.

'Let #146;s go back to basics for a second and see if that gets us anywhere,' he said. #145;We know that the Ganymeans evolved on Minerva #151;right?' The heads around him nodded in assent. 'We also know that the Ganymeans must have visited Earth because there #146;s no other way they could have ended up with terrestrial animals on board their ship #151;unless we #146;re going to invent another hypothetical alien race and I #146;m sure not going to do that because there #146;s no reason to. Also, we know that the ship found here on Ganymede had come to Ganymede from Minerva, not directly from Earth. If the ship came from Minerva, the terrestrial animals must have come from Minerva too. That supports the idea we #146;ve already got that the Ganymeans were shipping all kinds of life forms from Earth to Minerva for some reason.'

Paul Carpenter held up a hand. 'Hang on a second. How do we know that the ship downstairs came here from Minerva?'

'The plants,' Fichter reminded him.

'Oh yeah, the plants. I forgot. . .' Carpenter subsided into silence.