life on earth, glided over our young world ages ago."
"If there were such things then, why couldn't they have left descendants like them?" Ross argued.
Woodin shook his head. "Because they all vanished ages ago, changed into different and higher forms of life, starting the great upward climb of life that has reached its height in man.
"Those long-dead, single-celled protoplasmic creatures were the start, the crude, humble beginnings of our life. They passed away and their descendants were unlike them. We men are their descendants."
Ross looked at him, frowning. "But where did they come from in the first place, those first living things?"
Again Woodin shook his head. "That is one thing we biologists do not know and can hardly speculate upon, the origin of those first protoplasmic forms of life.
"It's been suggested that they rose spontaneously from the chemicals of earth, yet this is disproved by the fact that no such things rise spontaneously now from inert matter. Their origin is still a complete mystery. But, however they came into existence on earth, they were the first of life, our distant ancestors."
Woodin's eyes were dreaming, the other two forgotten, as he stared into the fire, seeing visions.
"What a glorious saga it is, that wonderful climb up from crude protoplasm creatures to man! A marvelous series of changes that has brought us from that first low form to our present splendor."
"And it might not have occurred on any other world but earth! For science is now almost sure that the cause of evolutionary mutations is the radiations of the radioactive deposits inside the earth, acting upon the genes of all living matter."
He caught a glimpse of Ross' uncomprehending face, and despite his raptness smiled a little.
"I can see that means nothing to you. I'll try to explain. The germ-cell of every living thing on earth contains in it a certain number of small, rod-like things which are called chromosomes.
"These chromosomes are made up of strings of tiny particles which we call genes. And each of these genes has a potent and different controlling effect upon the development of the creature that grows from that germ-cell.
"Some of these genes control the creature's color, some control his size, some the shape of his limbs, and so on. Every characteristic of the creature is predetermined by the genes in its original germ-cell.
"But now and then the genes in a germ-cell will be greatly different from the genes normal to that species, and when that is so, the creature that grows from that germ-cell will be greatly different from the fellow-creatures of its species. He will be, in fact, of an entirely new species. That is the way in which new species come into existence on earth, the method of evolutionary change.
"Biologists have known this for some time and they have been searching for the cause of these sudden great changes, these mutations, as they are called. They have tried to find out what it is that affects the genes so radically.
"They have found experimentally that X-Rays and chemical rays of various kinds, when turned upon the genes of a germ-cell, will change them greatly. And the creature that grows from that germ-cell will thus be a
