Proceedings of the National Academy of Sciences of the United States of America. 5/13/2003, Vol. 100 Issue 10, p5902. 6p. 8 Color Photographs, 1 Chart, 5 Graphs.
Proceedings of the National Academy of Sciences of the United States of America. 5/13/2003, Vol. 100 Issue 10, p5896. 6p. 3 Diagrams, 3 Charts, 1 Graph.