Proceedings of the National Academy of Sciences of the United States of America. 1/24/2006, Vol. 103 Issue 4, p982-987. 6p. 3 Color Photographs, 6 Diagrams, 10 Graphs.
Proceedings of the National Academy of Sciences of the United States of America. 2/18/2003, Vol. 100 Issue 4, p1775. 6p. 31 Black and White Photographs, 6 Diagrams, 5 Graphs.