On the Cover
July-August 1999 Volume 87, Number 4
Recent ice- and ocean sediment-core studies have revealed that the
average global atmospheric temperature has changed as much as 10 degrees
Celsius in less than 20 years. In "Rapid Climate Change," Kendrick
Taylor reviews the evidence for such changes and raises the question of
whether greenhouse-induced warming may precipitate a return to an
ice-age climate. ...
New evidence shows that earth's climate can change dramatically in only a decade. Could greenhouse gases flip that switch?
A discovery that could revolutionize medicine raises the question of where to draw the line on human embryonic research
Pleasure or pain? Social response or reflex? Tickling and the laughter it induces are an enigmatic aspect of our primate heritage
The asymmetry of the amino acid molecules found in all living things may have originated in space billions of years ago
No longer limited to warding against infectious agents, vaccines may help treat diseases after they have been diagnosed
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