There it was last week, in newspapers and, as follows, high up the CNN Web site: “The Scottish scientist credited with successfully cloning Dolly the sheep last year has admitted he may have made a procedural mistake⃛ ‘There is a remote possibility that the cell came from a fetus rather than an adult,’ Ian Wilmut said.⃛” Recently in Science, an attack on the original Nature paper met with a rebuttal from the original authors. But has the public been misled?

No more than in any significant but scientifically controversial development. One controversy concerns the burden of proof. How burdensome must it be, in an area where experiments are both time-consuming and complex? With hindsight (and few could have anticipated the extent of the fuss stimulated by Dolly), it is always easy to claim that the proof was inadequate. But the definition of the threshold of proof is itself controversial, particularly given the significance that the results have taken on. According to soundings across the relevant research community (see page 825), the published attack represents an extreme position in its demands for proof. And according to encouragingly many, the probability that the paper's results are valid remains high. But this case is yet another illustration of the truism that a formal scientific publication need not necessarily be the last word.

In the meantime, the journals give formalized expression to the buzz of gossip and debate within the community. That debate, as it seeps out, can undermine in the public eye even the most rigorously justified claim. Yet whatever the risks for public perception, it is important that the plurality of scientific views is expressed in the open — which is where informal opinion in news and correspondence pages or on the Web plays its valuable part. It is also important that the public should recognize the current debate for what it is: scientists behaving critically, as they should. Most importantly, it is premature to draw any conclusions from the absence so far of a second mammal cloned from adult cells.