Professor of Cell and Developmental Biology and Howard Hughes Medical Institute Investigator Phillip Newmark and his colleague James Sikes have found an answer to a vexing biological riddle.

Why some planarians can so easily regenerate a head but others can't is a question that has long puzzled scientists. "This is really a classic problem in the field," says Newmark.

Now, three teams of researchers have not only zeroed in on the biological reason for this limitation, they've also managed to restore the worms' full regenerative abilities by manipulating a single genetic pathway.

The findings appear in the journal Nature.