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  1. Health & Medicine

    Sometimes an antibiotic is much more

    By reining in destructive enzymes in the body, tetracyclines can thwart various diseases, including periodontal bone loss and cancer.

    By Janet Raloff
  2. Paleontology

    Extinctions Tied to Impact from Space

    Evidence trapped in 250-million-year-old sediments may help researchers pin the ultimate blame for the massive extinctions that occurred then on the impact of an extraterrestrial object about 9 kilometers across.

    By Sid Perkins
  3. Math

    Appealing Numbers

    The ancient Greeks, especially the Pythagoreans, were fascinated by whole numbers. They defined as “perfect” numbers those equal to the sum of their parts (or proper divisors, including 1). For example, 6 is the smallest perfect number-the sum of its three proper divisors: 1, 2, and 3.