“Have you been able to do much work on the higher animals?” Matthew asked. “Lityansky didn’t seem to have looked at anything as complicated as the slug, let alone the mammal-analogues.”

“When I first came here,” Tang said, “I was excited by the possibility that we might be able to go straight to the top, as it were, by recovering some genetic material from the city-builders, but the quest has so far proved frustrating. We know that there are monkey-analogues further downstream, which are presumably the nearest relatives of the humanoids so far observed, but our attempts to trap mammal-analogues in and around the ruins have been just as frustrating as our attempts to discover humanoid remains. The river expedition was, of course, intended to compensate for those disappointments. I assume that it still is. One of my fallback projects—fortunately, as it has turned out—was to investigate the class of creatures that includes the one that incapacitated poor Maryanne. My initial interest had nothing do do with the fact that all the species in the group are poisonous, but the work Maryanne and I have done on the toxins has proved very useful. You’ve presumably been informed that the genomics of organisms like this one seem unusually complex even if one sets aside the matter of the second coding molecule. The genomic potential of the DNA-analogue seems to be far more elaborate than its representation in quotidian proteomics.”

Matthew had little difficulty in cutting through Tang’s excessively pedantic choice of terminology, which inevitably tempted him to an opposite extreme. “You mean that it has more genes than it seems to be using at any one time,” Matthew chipped in. “In other words, the orthodox exon-bank has all kinds of tricks up its sleeve—just the sort of thing that a serial chimera would need.”

Tang didn’t take offence at the crudity of Matthew’s presentation. Indeed, he recognized its propriety with a smile. “That’s one possible interpretation,” he agreed. “But let’s not forget the example of the humble frog.”

Matthew nodded to signify that he took the biochemist’s point. Earthly genomic analyses had shown that the relationship between genomic complexity and physical complexity wasn’t a simple one. In spite of their metamorphic capability, frogs were fairly low down on the complexity scale, but they had very bulky genomes because they maintained several parallel sets of genes for performing such seemingly simple tasks as determining the conditions in which their eggs could hatch. On the other hand, that same flexibility extended to patterns of development in early embryos—which was exactly the kind of versatility that might be an interesting consequence of the relative complexity of Tyrian genomes. “Have you made any progress figuring out what the presently unexpressed genes might be for?” he wanted to know.

“Yesterday, I would have had to say no,” Tang said. “Today …” He paused in order to wave a languid hand at his prize specimen before picking up the story. “It’s not just bigger than the other specimens I’ve seen. The mass-surface area considerations that affect growth and form are universal. It hasn’t got legs, so it doesn’t suffer from the supportive problems that affect so many Earthly animals, but the tentacles pose a similar problem. The muscular strength needed to move them increases geometrically in proportion to their length. That could be accomplished straightforwardly by adding muscular bulk, but it isn’t. The structural materials framing the muscle are different. Either a different set of genes has come into play, or the exons are teaming up according to a different pattern. Ike will suspect the latter, of course, but he’s primed to look for gene-nesting explanations. He and I will have to get together to see if we can fit the proteomics to the genomics.”

“That might help to explain why the local invertebrates don’t use a chitin-analogue in their exoskeletal components,” Matthew said. “The advantages of hardness and strength have to be set against the disadvantages of inflexibility. Earthly insects have to shed their exoskeletons if they want to get bigger. Here, where versatility is the order of the day, they use an entirely different set of molecules because it makes it easier to ring the changes.”

“Quite possibly,” Tang agreed. “It remains to be seen, of course, how flexible the system might be. So far, I’ve only had the opportunity to observe relatively minor variations of size and form. Until I find a much bigger giant, or manage to identify two radically different forms of the same chimerical cell-mix, it’s all conjecture.”

“Have you searched the flying-eye data for giant slugs that might be blown-up versions of this one?” Matthew asked.

“Not yet,” was the suitably guarded reply.

“But even if we keep the frog example in mind— especiallyif we keep the frog example in mind—it’s plausible that the extra genes in the DNA-analogue part of the genome include metamorphic options. Options that remain permanently in place, rather than simply guiding a growing individual through a fixed series of stages.”

“It’s all speculative, at present” Tang said. “But yes, those are the lines along which we’ve all been thinking. The parallel systems in frogs are all to do with reproduction—the options can determine the sex of hatchlings as well as facilitating development at a range of different temperatures—so it’s possible there’s a reproductive function here, if only we could figure out exactly how these creatures do reproduce. I’m no anatomist, but I can’t find anything resembling sex organs in this specimen or any of its kin. Andrei Lityansky undoubtedly told you about Bernal Delgado’s speculations about chimerical renewal and exchange, but I’m afraid that I haven’t been able to find any supportive evidence for the kinds of process he imagined. If the organisms are very long-lived, they might not bother to maintain their sex organs permanently—they might develop them temporarily just for the mating season. There are Earthly examples … but the simple fact is that we don’t know.”

“That thing isa chimera, I suppose,” Matthew said, pointing yet again at the creature in the biocontainment cell. “Is it a more complicated chimera than its smaller kin?”

“Oddly enough, no. When I began investigating the specimen I half-expected to find far more extensive chimerization than the smaller specimens exhibit, but it’s a mosaic of eight genetically distinct but phenotypically similar cell-types, which is exactly the same level of complexity as specimens with a tenth of its body mass, and less than some thumb-sized individuals of other kinds. Eight is by far the most frequent figure that turns up—four is only half as common, sixteen less than a quarter. Two crops up fairly regularly, but I haven’t yet found a thirty-two—or, for that matter, a singleton.”

“What about the mammal-analogues?” Matthew asked.

“The work that’s been done at Base One hasn’t turned up anything but fours and eights. That’s disappointing, in a way. There doesn’t seem to be any correlation between phenotypic complexity and chimerical complexity—but everything we’ve examined thus far has been a simplechimera in the sense that all the cells are closely related—often sibs or half-sibs. Again, it all comes back to reproduction. If they don’t grow temporary sex organs for the mating season they may well indulge in periodic radical experiments in chimerization, but …

“Until we catch them at it,” Matthew finished for him, “we have no way of knowing whatthey get up to.”

It wasn’t quite the way Tang would have put it, but he nodded agreement regardless.

“How much hidden potential are we talking about?” Matthew wanted to know. “Setting aside worries about the frog example, how versatile might these beasts be when they’re not cruising in neutral?”

That was a step too far for Tang. “I really can’t say,” the biochemist told him, sadly. “Before I could make any sort of guess I’d have to know what kindof potential it is. I’d be very interested to know what might trigger its release, if you had any ideas on that score.”