Today, we visit a home that hardly changed in a quarter-million years. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

I've said a lot about the way we're driven by our technologies. I've talked about the symbiotic way we live with the fruits of our minds -- the way we interact with our tools. I've said that our machines are extensions of our minds -- that they teach us, form us, and make us what we were not.

But it was not always so. While human creatures have been on this earth a long time, the man-machine interaction has gone on only in the last one percent of human existence.

Author Jean Kerisel writes about soil mechanics and foundations. He begins by showing us how early humans understood and controlled their soil. He takes us into Choukoutien Cave -- 25 miles outside Beijing, China.

Early Peking Man settled the cave 560,000 years ago. It was then a large limestone karst formation. It had stalactites and stalagmites and a sloping floor that ended in water catch-basins. The cave was occupied for 230,000 years. The bottom gradually filled in with layer after layer of detritus, and the floor gradually rose. The occupants broke away the stalactites and extended the ceiling and walls. At one point the central chamber was 450 feet wide.

Archaeologists have been sifting downward through the millennia. The earliest tools they find are crude sandstone implements. Later, they were sharper and smaller and made of harder stone. The later tools reflect some knowledge of splitting and shaping stone. Those later occupants also showed an elementary sense of structural form -- of arches and rounded vaults.

Yet that seems like little gain in a quarter-million years. We wonder how far ahead of dam-building beavers or hive-making honey-bees these people were. We seem to be watching instinct at work more than human creativity.

We ask so much more of our technology. We expect it to change, and we let it change us. That didn't happen in the quarter-million years our ancestors occupied that cave. Their technology was too sparse. Its critical mass was not enough to make them see its creative possibilities.

So their bones and ashes and castoff tools filled up the floor and eventually drove them out the top. They moved on to some other cave and continued their almost static lives for hundreds of millennia more. Only the other day -- only 30,000 years ago -- did something change. Suddenly our tools opened our eyes to a stunning range of possibility. Suddenly, in a blink, they changed us into a radically different species.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Kerisel, J., Down to Earth. Boston: A.A. Balkema, 1987, Chapter 1.