All human flu strains evolved from flu viruses that live in birds. To understand how these transitions happen, scientists have recently been tinkering with a strain of bird flu to see how many mutations it takes until it spreads from mammal to mammal.

When news of their efforts emerged last fall, a fierce debate broke out about the wisdom of publishing the experiments in full.

Eventually, the scientists got the go-ahead from a federal advisory board, and earlier this year they described how a few mutations of a strain called H5N1 enabled it to spread among ferrets.

Last fall, 162 dead harbor seal pups washed up on the beaches of New Hampshire and Massachusetts.

In a paper published today in the journal mBio, a team of scientists reports that the pups were killed by a new strain of influenza.

Their research indicates that the virus evolved from bird flu, gaining the ability to spread from seal to seal — a real-life example of the transformation that scientists have been exploring in their labs.

Eddie Holmes, an expert on flu evolution at Penn State who was not involved in the research, believes the new virus needs to be carefully monitored to see what sort of threat, if any, it poses.