In the first surprise to emerge from mankind's newly deciphered genetic code, humans appear to be only slightly more genetically complex than flies, worms and other of Earth's lowliest creatures.
The finding comes as part of two landmark papers to be published this week by the rival teams of scientists who last summer decoded the 3 billion chemical building blocks that make up human DNA.
The research is expected to touch off a renaissance not just in biology, but every corner of the scientific world. Hidden in the genetic code, scientists say, is everything from new cures for human disease to answers to how mankind evolved.
"We are standing at an extraordinary moment in scientific history," said Eric Lander, director of the Whitehead Institute Center for Genome Research in Cambridge, Mass. "It's as though we have climbed to the top of the Himalayas. We can, for the first time, see the breathtaking vista of the human genome."
One scientific team, an international consortium of more than 20 publicly funded research centers known as the Human Genome Project, is publishing its results in the British journal Nature. The other team, start-up Celera Genomics of Rockville, will publish in Science. Both will be available on the Internet tomorrow.
In their reports, the scientists estimate human DNA contains from 26,000 to 40,000 genes - far below previous estimates as high as 120,000.
By comparison, they point out, the worm C. elegans has 19,000 genes, while the fruit fly has roughly 13,600 genes. Humans, in fact, have only five times more genes than some bacteria.
"It seems to be some kind of affront to human dignity," Lander said.
The finding "will undoubtedly trigger scientific, ethical, philosophical and religious questions throughout the beginning of this new century," noted geneticist Jean Michele Claverle in a separate essay in Science.
One explanation for the puny number of genes in human DNA, scientists say, is that genes are far more complex than once thought.
"The notion that one gene equals one disease or that one gene produces one key protein is flying out the window," said J. Craig Venter, head of Celera.
The small number of genes is just one of the provocative findings to emerge from the preliminary analysis of the entire genome:
Not only do humans have fewer genes than expected, but some come from an unusual source. Scientists, for example, found that more than 200 genes in the human genome seem to be hand-me-downs from bacteria.
Men appear twice as likely to pass on genetic mutations as women. The finding, which confirms recent research, is a mixed message for men: While it suggests men are the engine for evolutionary change, they might also be introducing more disease-causing genetic glitches than women.
As scientists have long suspected, while the world's peoples may come in different sizes and colors, they appear to be nearly identical on the inside - differing by just one out of every 1,000 genetic letters.
The research also sheds new light on "junk DNA," the highly repetitive stretches of genetic building blocks that fill up much of the genome.
This genetic debris has mystified biologists for decades and was thought to have no major biological role. But evidence from Celera scientists that junk DNA makes up more than one-third of the genome suggests it may be more important than once thought.
"It doesn't make a lot of sense to us that you're carrying around that big a trash can," said Andrew Feinberg, a geneticist at the Johns Hopkins University.
"That stuff in between the genes isn't junk."
Finally, researchers identified more than 1.4 million variations in the human genetic code that may not only lead to new therapies but answer some fundamental questions about human origins.
These differences, known as single nucleotide polymorphisms ("SNiPs"), hold the key to susceptibility to illnesses such as cancer, diabetes and heart disease, and individual responses to medication.
The publication of the landmark research brings to a close one of the most bitter competitions in the history of science.
Or so it was thought.
Despite a public truce at the White House last summer to celebrate the completion of the sequencing of the genome, Celera and the public consortium are once again at odds - this time over availability of genome data.
The spat exposes one of the most important issues facing science in the new century: how to balance the tradition of open scientific inquiry with the interests of for-profit research labs, where more and more groundbreaking science occurs.
Although the two groups were initially planning to publish their research side by side, in December scientists with the Human Genome Project decided to submit their research to the rival publication Nature.
The move was intended to protest Celera's decision to put restrictions on how its genome data could be used.
In the past, researchers have customarily deposited their genetic data in the online database GenBank, but Celera will keep its database on its own Web site.
"We would have preferred that they posted it in GenBank," said Don Kennedy, editor in chief of Science. "We're stuck with the present choice."
While the publication of the decoded human genome marks the end of a long and expensive struggle, scientists on both sides say the work has just begun. Ten percent of the genome remains to be pieced together.
Then the real challenge, the Celera group concluded, "will lie ahead as we seek to explain how our minds have come to organize thoughts sufficiently well to investigate our own existence."
Wire reports contributed to this article.