om the day the crash program had been started, the job was
completed. Jason Wall had spent the last few days watching the world at
play. Happy children, contented people, folks who didn't have much, but
who did have happiness. They would go right on enjoying themselves,
after Jason Wall died. It wasn't fair, he told himself. And he would see
to it that they didn't--by destroying their first ancestor, and his, so
they would never be born, so the human race would never be....

"... all physical actions on the sub-microscopic level, on the level of
molecules and atoms and sub-atomic particles and quanta of energy--all
these actions," the chief physicist told Jason Wall, "are reversible. If
you can control the reversal, you can return matter, energy, and space
to its former state. Doing that, you travel through time. Therefore--"

"Never mind the details," Jason Wall snapped. "That's your department. I
only want to know this: will it work. Will it take a man back through
time."

"Yes, but--"

"Very well. I'll go."

"But we haven't figured out a way to return. If you go, you won't come
back. You'll have to spend the rest of your life back there."

The rest of his life. Jason Wall smiled. The rest of his life could be
measured in pain-wracked months, possibly only in weeks.

Fifteen minutes after his discussion with the chief physicist, he sat
down in the time chair. Anthropologists had been consulted for the final
stages of the project. There would be no mistakes. He would go where and
when he had to go....

"Ready, sir?"

"Ready," said Jason Wall. Ready to destroy the human race--

His vision flashed and blurred. Time moved backward for him.

* * * * *

A forest trail. Animals used it, had carved it out of the wall of
jungle. And the first man?

Armed with a revolver, Jason Wall left the now useless time-chair and
hid himself beside the trail. He waited three days, living on berries
and a small marsupial creature he had caught with his bare hands. If
First Man was around, he didn't want to frighten him off with gun-fire.

At last, First Man came.

He was, Jason Wall observed with objective detachment, a noble-looking
creature. The first true man. Over six feet tall, perfectly
proportioned. He looked quite the healthiest man Jason Wall had ever
seen. If looks meant anything, he had never known a day of disease in
his life, and never would. Jason Wall's determination to kill gr