nature's preservative

Prove It!
That's What the Skeptics Say...

Claims of recovering whole organisms -- or even intact DNA -- from ancient amber are sure to arouse skepticism. One of the most prominent critics has been biochemist Tomas Lindahl, of the Imperial Cancer Research Fund, who, at a meeting in Washington, D.C. (see Fact, Fiction, and Fossil DNA in the bibliography), compared the recovery of DNA from millions of years ago to the recent less-than-meets-the-eye furor over cold fusion.

Lindahl focused on the need to replicate experiments, and on the fact that DNA degrades, under most conditions, in days, months, or years, not to mention millions of years. He also questioned whether irreplaceable samples should be destroyed for the sake of extracting DNA.

Rob DeSalle, associate curator at the American Museum of Natural History (AMNH), says most of Lindahl's criticisms are "absolutely valid," and that many of them have improved techniques among amber researchers.

Containing Contaminants
For example, scientists are spending more time replicating their work, typically in other labs, where different contaminants would be expected. When DeSalle and David Grimaldi helped recover sequences from a termite several years ago, DeSalle says, they did not send the samples elsewhere. Today, he says, "I'd probably send them to the British Museum" for replication (defined).

Still, DeSalle says, not all of the criticism is on the mark since enough is known about DNA to make it its own evidence. In particular, DNA changes through the years and scientists know how to read the pace of those changes to date an organism. "You can show, using a scientific method called phylogenetic analysis, that these [DNA] sequences are valid," says DeSalle. "The fossil sequences have accrued enough changes to indicate they are different from living, morphologically (defined, see morphology) similar species, but have retained certain key nucleotides that indicate close relatedness of the fossil to the living taxa (defined, see taxon).

Furthermore, the rate of degradation in DNA depends critically on the environment, and the exclusion of water and oxygen in amber may be enough, some scientists think, to preserve the information-rich molecule.

Finally, DeSalle says, the concern over destroying samples has hit home among some amber researchers. "We have stepped back from the work. ... We destroyed a fossil, and we didn't get that many DNA characters." Before opening up more samples, DeSalle says, "we're trying to develop techniques that allow you to get 10 to 20 times as much sequence from each fossil. Until then, I don't think it's useful to be breaking these fossils."

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