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The 25 most provocative questions facing science -- the NY Times. From question #18, quotable:

Dr. Stephen Jay Gould, the late Harvard paleontologist, crystallized the question in his book "Wonderful Life." What would happen, he asked, if the tape of the history of life were rewound and replayed? For many, including Dr. Gould, the answer was clear. He wrote that "any replay of the tape would lead evolution down a pathway radically different from the road actually taken."

In fact, to many scientists, it would seem impossible to re-evolve anything like life on earth today, given how life has been shaped by accidents large and small.

But 12 flasks of bacteria in East Lansing, Mich., are beginning to challenge such notions. In 1988, Dr. Lenski and his colleagues set up a dozen genetically identical populations of E. coli bacteria in bottles of broth and have followed their evolutionary fates.

Now, more than 30,000 bacterial generations later, Dr. Lenski and colleagues have what is becoming one of the most striking examples of repeatability yet. All 12 populations show the same patterns of improvement in their ability to compete in a bottle and increases in cell size. All 12 have also lost their ability to break down and use a sugar, called ribose.

More surprising, many genetic changes underlying these adaptations are very similar. Every population, for example, lost its ability to break down ribose by losing a long stretch of DNA from the same gene.

Other scientists studying cichlid fish have observed how the same varieties of cichlids evolve anew every time they invade a new lake. And Dr. Rieseberg and colleagues have found evidence that evolution can repeatedly produce the same species.

These scientists found that one sunflower species on sand dunes has evolved independently three separate times. And each time one of the species newly evolves, genetically it appears to turn out much the same. "With these species, there seems to be only one way to do it," Dr. Rieseberg said.

Some scientists, like Dr. Simon Conway Morris, a paleobiologist at the University of Cambridge and ardent critic of Dr. Gould's view, say the evidence for repeatability is rampant. He argues in his new book, "Life's Solution: Inevitable Humans in a Lonely Universe," that some features are so adaptive that they are essentially inevitable — like the ability to see and, as his title suggests, the intelligence and self-awareness that are the hallmarks of humanity.

And note well question #9 -- "When will the next Ice Age Begin?"