Louise Leakey puts aside an antelope tooth dating from about 2 million years ago and clicks her laptop computer into suspend mode.

Why not just turn it off?

"Because it takes an eternity to boot up," she says.

They say that time is relative, and no family says it with more authority than the dynasty that Louise Leakey, at 27, embodies. The Leakeys of Kenya have done more than perhaps any other scientists to put into perspective just how fleeting 1,000 years really is in the context of human life on Earth.

The family tree of these paleontologists spans the 20th century: In 1902, the missionary parents of Louis Leakey arrived in Nairobi. For Christmas 1915 they gave him a copy of "Days Before History," and the die was cast. Louis Leakey married Mary Nicol, who gave birth to Richard Leakey, whose wife Meave today labors in the paleontology wing of the National Museums of Kenya two doors down from their daughter, Louise, a doctoral student who is learning the family business.

The courtyard below is dominated by a statue of Louis Leakey, hunched happily over a pile of bones. In his posture is something distinctly simian.

"Leakeys tend to be brought up in the field, looking for bones," said Meave Leakey, who brought her daughter into the wastes of northern Kenya two weeks after she was born. The family had an exciting new dig going at a place called Lake Turkana, an arid stretch of the Great Rift Valley that Richard Leakey, looking from an airplane, decided was a promising fossil site. The promise was realized, first with a complete skull of Australopithecus that Richard Leakey proudly presented to his mother ("It's beautiful!" Mary Leakey exclaimed), and most famously with a nearly complete skeleton of a 9-year-old Homo erectus dubbed Turkana Boy.

After Richard Leakey devoted himself to politics--he is now reforming the impressively corrupt and inefficient Kenyan civil service--field work became the province of women. And in the way Meave and Louise talk about that work in interviews--what gets them excited, what they take for granted--speaks volumes about human life in 2000, and how different it is from the past.

Mother and daughter make expeditions to Turkana each summer, often working on opposite sides of the lake in the dried riverbeds. As they cut through the earth, these waterways pulled into the open the contents of sediment that, in the Great Rift Valley, can be quite old.

"What we do is divide the time," Meave said of how they work. "She works up to 3 million, or 1 1/2 to 3. And I work from 3 million to 4 million."

This is said off-handedly. Geological time is shop talk. And so vast as to defy grasp. Never mind that the Earth might be 3 billion or 4 billion years old. Consider instead the footprints uncovered in Tanzania by a team led by Mary Leakey, Meave's late mother-in-law, Louise's grandmother. Vivid and distinct, the footprints showed that an ancestor of modern man was walking upright 3.6 million years ago, when the mudpan a pair of them strolled across was being transformed to something like concrete by a light shower of volcanic ash.

To put 3.6 million years in perspective, imagine a day that lasted 1,000 years. Then imagine 10 years of such days.

You can't, of course. But you can learn what a human bone looks like, and what animal bones look like. "Antelopes from pigs and hippos from elephants--that you can tell when you're 5," said Louise Leakey. Eyeballing is the essence of paleontology, strolling in a fossil field, looking for things you recognize.

What has changed is what can be learned from the bits and pieces back at the lab.

"Oh, you can't believe what you can do now!" Meave said. Technology has given scientists new ways of seeing. A CT scan lets you see inside the bony labyrinth of an ear, the key to balance, and thus to whether the fossil's creator walked on two feet or four.

"And now you have these computers!" Meave Leakey said, seated beside a PowerBook G3. "The whole thing has changed so much you can't imagine. Louise, doing her thesis. She goes into a room and comes out five minutes later with a graph. I did that by hand in 1967!"

It's the familiar wonder about the pace of change, but in this case it frames one of the greatest wonders of all: The rise of applied science, Meave said, not only has made it easier to track the evolution of humans from the still-missing link where humans left apes behind. Technology also has lifted the human species clean out of the theory that saw it this far: natural selection.

"We don't allow natural selection to occur any more," Meave Leakey said. "Genetic disorders are cured now. You don't get the fine tuning of desirable traits."

Her tone is carefree, with just a hint of warning. "If you take natural selection away, all the disadvantageous genes get through. In the end, you'll get a much less healthy population getting through.

"At the same time," Meave Leakey said, "I think the research on genetics and the ability to select genes is maybe going to salvage that problem. I'm sure it will. But there are so many implications for that."

Her daughter comes in to be photographed. Her mother grooms her, picking lint off her blouse.

Visitors to Africa, where scientists believe humans were created--only leaving for Asia and Europe about 100,000 years ago--often say they feel at home here.

"Maybe it's the hospitality," Meave Leakey said. Or maybe its something of the feeling she gets in Turkana.

"There's this incredible sense of peace, of continuity," she said. "And that this is part of this longer, bigger system. That we're not very significant in terms of the whole process, but we can understand it. And that's where our significance is."

CAPTION: Meave Leakey, holding skull unearthed in excavations near Lake Turkana, shares a casual moment with her daughter Louise at their workplace, the National Museums of Kenya.