The improbable origins of life on Earth

We do not yet know how, where, or why life first appeared on our planet. Part of the difficulty is that "life" has no strict, universally agreed-upon definition.

Study reveals how some bacterial infections become chronic

In the early 1900s, a cook named Mary Mallon, better known as "Typhoid Mary," spread Salmonella Typhi, the causative agent of typhoid fever, to dozens of her patrons even though she showed no symptoms. Many people today harbor ...

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