© Maddie McGarvey for The New York Times

Loggers are finding it impossible to profitably harvest some federal forests. That leaves more fuel for fires to accumulate.

© Ethan Swope/Associated Press

We asked 100 scientists about unsolved problems in their fields. They sent back provocations — on the origins of life, the possibilities for human progress and much more.

© Photo illustration by Jane Stockdale for The New York Times

Some viruses appear to vanish when outbreaks dissipate, only to emerge again. Scientists don’t always know which animals they lurk in — and how to stop them from spilling back over.