"The melted lava poured into the ocean!"
"The land rose from the sea!"
"The lightning hit the water!"
"The squirmy things were so ugghhy!"
Teacher nodded and smiled and ignored the last comment. He had no idea why Mandi-2 was registered in this science course and had a strong feeling she would not stay long.
"Very good. So now we reach the annelids, like our worm here. Segmented, with each segment almost living a life of its own. Here are the first blood vessels to carry food to all the tissues most efficiently. Here is the first hemoglobin to carry oxygen to all the cells. Here is the first heart, a little pump to force the blood through those tubes. But one thing is missing yet. Do you know what it is?"
Their faces were empty of answers, their eyes wide with expectation.
"Think about it. What would have happened if Grosbit-9 had really stepped on this worm?"
"It would have squashed," Agon-1 answered with eight-year-old practicf lity. Mandi-2 shivered.
"Correct. It would have been killed. It is soft, without a shell or a skeleton. Which brings us to the next branch on the evolutionary tree."
Teacher pressed the activating button on the control unit at his waist, and the programmed computer seized them and hurled them through time to their next appointment. There was a swift, all-encompassing grayness, with no feeling of motion at all, which vanished suddenly to be replaced by a green dimness. Twenty feet above their heads the sun sparkled on the surface of the ocean while all about them silent fish moved in swift patterns. A great monster, all plates and shining teeth, hurried at and through them and Mandi-2 gave a little squeal of surprise.
"Your attention down here, if you please. The fish will come later. First we must study these, the first echinoderms. Phill-4, will you point out an echinoderm and tell us what the term means?"
" 'Echinoderm.’ " the boy said, keying his memory. The training techniques that all the children learned in their first years of schooling brought the words to his lips. Like the others he had a perfect memory. "Is Greek for spiny skin. That must be one there, the big hairy starfish."
"Correct. An important evolutionary step. Before this, animals were either unprotected, like our annelid worm, or had skeletons outside, like snails or lobsters or insects. This is very limiting and inefficient. But an internal skeleton can give flexible support and is light in weight. An important evolutionary step has been made. We are almost there, children, almost there! This simple internal skeleton evolved into a more practical notochord, a single bone the length of the body protecting a main nerve fiber. And the chordates, the creatures with this notochord were only a single evolutionary step away from this — all this!"
Teacher threw his arms wide just as the sea about them burst into darting life. A school of silvery, yard-long fishes flashed around and through the students, while sharp-toothed sharklike predators struck through their midst. Teacher's speech had been nicely timed to end at this precise and dramatic moment. Some of the smaller children shied away from the flurry of life and death while Grosbit-9 swung his fist at one of the giants as it glided by.
"We have arrived," Teacher said, vibrantly, carried away by his own enthusiasm. "The chordate give way to the vertebrate, life as we know it. A strong, flexible internal skeleton that shields the soft inner organs and supports at the same time. Soft cartilage in these sharks— the same sort of tissue that stiffens your ears — changes to hard bone in these fishes. Mankind, so to speak, is just around the corner! What is it, Ched-3?" He was aware of a tugging on his toga.
"I have to go to the—"
"Well press the return button on your belt and don't be too long about it."
Ched-3 pressed the button and vanished, whisked back to their classroom with its superior functional plumbing. Teacher smacked his lips annoyedly while the teeming life whirled and dived about them. Children could be difficult at times.
"How did these animals know to get a notochord and bones?" Agon-1 asked. "How did they know the right way to go to end up with the vertebrate — and us?"
Teacher almost patted him on the head, but smiled instead.
"A good question, a very good question. Someone has been listening and thinking. The answer is they didn't know, it wasn't planned. The ever-branching tree of evolution has no goals. Its changes are random, mutations caused by alterations in the germ plasm caused by natural radiation. The successful changes live, the unsuccessful ones die. The notochord creatures could move about easier, were more successful than the other creatures. They lived to evolve further. Which brings us to a new word I want you to remember. The word is 'ecology' and we are talking about ecological niches. Ecology is the whole world, everything in it, how all the plants and animals live together and how they relate one to the other. An ecological niche is where a creature lives in this world, the special place where it can thrive and survive and reproduce. All creatures that find an ecological niche that they can survive in are successful."
"The survival of the fittest?" Agon-1 asked.
"You have been reading some of the old books. That is what evolution was once called, but it was called wrong. All living organisms are fit, because they are alive. One can be no more fit than the other. Can we say that we, mankind, are more fit than an oyster?"
"Yes," Phill-4 said, with absolute surety. His attention on Ched-3 who had just returned, apparently emerging from the side of one of the sharks.
"Really? Come over here, Ched-3, and try to pay attention. We live and the oysters live. But what would happen if the world were to suddenly be covered by shallow water?"
"How could that happen?"
"The how is not important," Teacher snapped, then took a deep breath. "Let us just say it happened. What would happen to all the people?"
"They would all drown!" Mandi-2 said, unhappily.
"Correct. Our ecological niche would be gone. The oysters would thrivaand cover the world. If we survive we are all equally fit in the eyes or nature. Now let us see how our animals with skeletons are faring in a new niche. Dry land."
A press, a motionless movement, and they were on a muddy shore by a brackish swamp. Teacher pointed to the trace of a feathery fin cutting through the floating algae.
"The subclass Crossoptergii, which means fringed fins. Sturdy little fish who have managed to survive in this stagnant water by adopting thsir swim bladders to breathe air directly and to get their oxygen in this Jnanner. Many fish have these bladders that enable them to hover at any given depth, but now they have been adapted to a different use. Watch!"
The water became shallower until the fish's back was above the water, then its bulging eyes. Staring about, round and wide, as though terrified by this new environment. The sturdy fins, reinforced by bone, thrashed at the mud, driving it forward, further and further from its home, the sea. Then it was out of the water, struggling across the drying mud. A dragonfly hovered low, landed — and was engulfed by the fish's open mouth.
"The land is being conquered," Teacher said, pointing to the humped back of the fish now vanishing among the reeds. "First by plants, then insects — and now the animals. In a few million years, still over 255 million years before our own time, we have this…"
Through time again, rushing away on the cue word, to another swampy scene, a feathery marsh of ferns as big as trees and a hot sun burning through low-lying clouds.