In just two acres of a tropical forest, there can be as many species of trees as in all of the continental United States. In fact, the forests and coral reefs of the tropics are the world's most biologically diverse ecosystems. And because much of that diversity is still undescribed, and the contribution various species make to the stability of their ecosystems is still unexplained, the scientists at the Smithsonian Tropical Research Institute (STRI) in Panama won't be relaxing any time soon. Nor is theirs a local mission, despite the seeming limitation of "tropical." The knowledge they acquire studying marine and terrestrial life leaps the bounds of latitudes and advances our understanding of conditions that sustain life on a planetary scale. As an example, research on the capacity of rain forests to store carbon dioxide, and thereby mitigate the increasing levels of that gas in the atmosphere, is essential to the current debate about global climate change.
Smithsonian scientists arrived in Panama early in the 20th century, when biologists were needed to study insects carrying diseases that endangered workers building the canal. (See "Panama Turns 100," p. 44.) Because Panama happens to be ideally suited to the study of environmental stability and change, our scientists have been there ever since. The landmasses that are now North and South America floated free of each other for 65 million years. A mere three million years ago, the Isthmus of Panama rose from the oceans to form a land bridge between the continents. Once the bridge was in place, fauna and flora crossed from one to the other, to flourish or to die in their new homes.
Thanks to evolution, then, both geological and biological, Panama is rich in environments and species. Its landscape is marked by islands, coastal zones, mountain ranges, rain forests, and high-altitude elfin forests. Though separated by no more than the thin strip of the isthmus, the Atlantic and Pacific coasts of the country are radically different environments for marine life. More important, the known (and geologically recent) time of separation of organisms in the two oceans permits STRI researchers to ask—and answer—fundamental questions: How quickly do organisms evolve away from one another to become separate species? Do molecules of different organisms evolve at similar rates? If Pacific and Atlantic organisms were to come in contact once again, perhaps through a saltwater sea-level canal, would genetic changes keep them from interbreeding? And what aspects of the physical and biological environment drive those genetic changes in different groups?
STRI is now the world's largest and most innovative facility for the comprehensive study of tropical environments, with ten sites on the isthmus, a staff of more than 300, and as many as 500 scientists from around the world visiting in a typical year. The institute's programs of research and discovery radiate outward far beyond the lush locales of Panama, and theories to which evidence gathered on the isthmus gives rise are tested at other tropical sites in Latin America, Asia and Africa. Thus does the new knowledge gain legitimacy and force.
Construction cranes are not necessarily a welcome sight in a rain forest. But more than a decade ago, a STRI scientist realized that the machines might provide unprecedented access to one of earth's unexplored frontiers: the forest canopy, the vast exposed laboratory at the tops of trees where biosphere meets atmosphere and where so many new species have lately been discovered. To STRI scientists pursuing their investigation of the once-inaccessible zone from a gondola 100 feet off the ground, the terrestrial horizon may seem within reach. But a more important horizon, the boundary to their great progressive inquiry, recedes even as their knowledge advances. And to the benefit of us all, it draws them on.