"The basic reason for this difference, believe it or not, lay in the fact that Minerva was much farther away from the Sun." She went on to explain. "Life could never have developed on Minerva at all without the greenhouse effect, which you already know about. Even so, it was a cold planet, certainly in comparison to Earth.

"But this greenhouse effect kept the Minervan oceans in a liquid state and, as on Earth, life first appeared in the shallower parts of the oceans. Conditions there did not favor progression toward higher forms of life as much as on the warmer Earth; the evolutionary process was relatively slow."

"But intelligence appeared there much earlier than it did on Earth," somebody tossed in. "Seems a little strange."

"Only because Minerva was further from the Sun and cooled more quickly," Shilohin replied. "That meant that life got off to an early start there."

"Okay."

She resumed. "The patterns of evolution on the two worlds were remarkably similar to start with. Complex proteins appeared, leading eventually to self-replicating molecules, which in time led to the formation of living cells. Unicellular forms came first, then colonies of cells and after them multicelled organisms with specialized features--all of them variations on the basic marine invertebrate form.

"The point of departure at which the two lines went their own way, each in response to the conditions prevailing on its own planet, was marked by the appearance of marine vertebrates-- boned fishes. This stage marked a plateau beyond which the Minervan species couldn't progress toward anything higher until they had solved a fundamental problem that was not faced by their counterparts on Earth. The problem was simply their colder environment.

"You see, as improvements appeared in the Minervan fish species, the improved body processes and more highly refined organs demanded more oxygen. But the demand was already high because of the lower temperature. The primitive circulatory systems of the early Minervan fish couldn't cope with the dual workload of carrying enough oxygen to the cells, and of carrying wastes and toxins away from the cells--not if progress toward anything more advanced was going to be made, anyway."

Shilohin paused again to invite questions. Her listeners were too intrigued, however, to interrupt her story at that point.

"As always happens in situations like that," she continued, "Nature tried a number of alternatives to find a way around the problem. The most successful experiment took the form of a secondary circulation system developing alongside the first to permit load-sharing--a completely duplicated network of branching ducts and vessels; thus, the primary system concentrated exclusively on circulating blood and delivering oxygen, while the secondary took over fully the job of removing the toxins."

"How extraordinary!" Danchekker could not help exclaiming.

"Yes, I suppose that when judged by the things you're used to it was, Professor."

"One thing--how did the different substances find their way in and out of the right system?"

"Osmotic membranes. Do you want me to go into detail now?"

"No, er, thank you." Danchekker held up a hand. "That can wait until another time. Please continue."

"Okay. Well, after this basic architecture had become sufficiently refined and established, evolution toward higher stages was able to resume once more. Mutations appeared, the environment applied selection principles, and life in the Minervan seas began diverging and specializing into many and varied species. After a while, as you would expect, a range of carnivorous types established themselves. . ."

"I thought you said there weren't any," a voice queried.

"That came later. I'm talking about very early times."

"Okay."

"Fine. So, carnivorous fish appeared on the scene and, again as you would expect, Nature immediately commenced looking for ways of protecting the victims. Now the fish that had developed the double-circulatory-system architecture, who tended to be more advanced forms anyway because of this, hit on a very efficient means of defense: the two circulatory systems became totally isolated from one another, and the concentration of toxins in the secondary system increased to lethal proportions. In other words, they became poisonous. The isolation of the secondary system from the primary prevented poison from entering the bloodstream. That would have been fatal for the owner itself, naturally."

Carizan was frowning about something. He caught her eye and gestured for her to hold the conversation there a moment.

"Can't really say I see that as being much protection at all," he said. "What's the good in poisoning a carnivore after it's eaten you? That'd be too late, wouldn't it?"

"To the individual who was unfortunate enough to encounter one that hadn't learned yet, yes," she agreed. "But don't forget that Nature can afford to be very wasteful when it comes to individuals; it's the preservation of the species as a whole that matters. When you think about it, the survival or extermination of a species can depend on whether or not a strain of predators becomes established that has a preference for them as a diet. In the situation I've described, it was impossible for such a strain of predators to emerge; if a mutation appeared that had a tendency in that direction, it would promptly destroy itself the first time it experimented in following its instinct. It would never get a chance to pass its characteristic on to any descendants, so the characteristic could never be reinforced in later generations."

"Another thing too," one of the UNSA biologists interjected. "Young animals tend to imitate the feeding habits of their parents, on Earth anyway. If that was true on Minerva too, the young that managed to get born would naturally tend to pick up the habits of parents that avoided the poisonous species. It would have to be that way since any mutant that didn't avoid them wouldn't live long enough to become a parent in the first place."

"You can see the same thing in terrestrial insects, for example," Danchekker threw in. "Some species mimic the coloring of wasps and bees, although they are quite harmless. Other animals leave them alone completely--it's the same principle."

"Okay, that makes sense." Carizan motioned for Shilohin to continue.

"So marine life on Minerva developed into three broad fainilies: carnivorous types; nonpoisonous noncarnivores, with specialized alternative defense mechanisms; and poisonous noncarnivores, which possessed the most effective defense and were left free to carry on their development from what was already an advanced and privileged position."

"This didn't alter their resistance to cold then?" somebody asked.

"No, the secondary system in these species continued to perform its original function as well as ever. As I said, the only differences that had occurred were that the toxin concentration was increased and it became isolated from the primary."

"I got it."

"Fine. Now, the two types of noncarnivores had to eat, so they competed between themselves for what was available--plants, certain rudimentary invertebrate organisms, water-borne organic substances and so on. But Minerva was cold and did not offer an abundance of things like that--nothing like what is found on Earth, for instance. The poisonous species were efficient competitors and gradually became overwhelmingly dominant. The nonpoisonous noncarnivores declined and, since they constituted the food supply for the carnivores, the numbers and varieties of carnivores declined with them. Eventually two distinct groups segregated out of all this and from that time on lived separate lives: the nonpoisonous types moved out into the oceans away from the competition, and the carnivores naturally followed them. Those two groups evolved into a pattern of deep-sea life that eventually found its own balance and stabilized. The poisonous types retained the shallower, coastal waters as their sole preserve, and it was from them that land dwellers subsequently emerged."