Гарри Гаррисон - 50 in 50

They straggled towards Teacher, as slowly as they could. The bathers emerged dry from the ocean, while not a grain of sand adhered to skin or garment of the others. They gathered about Teacher, their chatter gradually dying away, and he pointed dramatically at a tiny creature writhing across the sand.

"Uhggh a worm!" Mandi-2 said and shivered deliciously, shaking her red curls.

"A worm, correct. A first worm, an early worm, a protoworm. An important worm. Although it is not on the direct evolutionary track that we are studying we must pause to give it notice. A little more attention, Ched-3, your eyes are closing. For here, for the first time, we see segmentation, as important a step in the development of life as was the development of multicellular forms. See, look carefully, at those series of rings about the creature's body. It looks as though it were made of little rings of tissue fused together — and it is."

They bent close, a circle of lowered heads above the brown worm that writhed a track across the sand. It moved slowly towards Grosbit-9 who raised his foot and stamped down hard on the creature. The other students tittered. The worm crawled out through the side of his shoe and kept on.

"Grosbit-9, you have the wrong attitude," Teacher said sternly. "Much energy is being expended to send this class back through time, to view the wonders of evolution at work. We cannot feel or touch or hear or change the past, but we can move through it and see it about us. So we stand in awe of the power that permits us to do this, to visit our Earth as it was millions of years ago, to view the ocean from which all life sprung, to see one of the first life forms on the ever-branching tree of evolution. And what is your response to this awe-inspiring experience? You stamp on the annelid! For shame, Grosbit-9 for shame."

Far from feeling shameful, Grosbit-9 chewed a hangnail on his thumb and looked about out of the corners of his eyes, the trace of a smirk upon his lips. Teacher wondered, not for the first time, how a 9 had gotten into this class. A father with important contacts, no doubt, high placed friends.

"Perhaps I had better recap for those of you who are paying less than full attention.” He stared hard at Grosbit-9 as he said this, with no apparent effect. "Evolution is how we reached the high estate we now inhabit. Evolution is the forward march of life, from the one-celled creatures to multicelled, thinking man. What will come after us we do not know, what came before us we are now seeing. Yesterday we watched the lightning strike the primordial chemical soup of the seas and saw the more complex chemicals being made that developed into the first life forms. We saw this single-celled life triumph over time and eternity by first developing the ability to divide into two cells, then to develop into composite, many-celled life forms. What do you remember about yesterday?"

"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."