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Photo of Anthony Coates Bridge That Changed the World

Tony Coates is a geologist and Deputy Director of the Smithsonian Tropical Research Institute. Following the Frontiers special Expedition Panama: Bridge That Changed the World, Tony answered viewers' questions about the formation of the Isthmus of Panama and its far-reaching consequences. Here are viewers' questions and his answers:

QWhat would happen if the Isthmus was not there? What do you think the world be like today?

If the isthmus of Panama was not there, the world would be very different today. All the animals of South America would be very different to today because they would never have been invaded and overtaken by all the species that colonized from North America. The Caribbean and the East Pacific would be one ocean with similar species; today they are very different with corals reefs abundant in the Caribbean but without large supplies of commercial fish, whereas the Pacific has few small coral reefs and large important commercial fisheries. Humans from Asia might not have reached South America via the Bering Land Bridge from the north so different kinds of humans might have arrived, say, from Polynesia. Columbus might have sailed on to Asia! The Ice Age would have been different and Europe's ports might freeze every winter like the Saint Laurence seaway does. El Nino and climates in other parts of the world might have been different in ways that we still do not fully understand.

QWould the shrimp you showed on the show [they had evolved on different sides of the isthmus after it formed] still fight if you started with young shrimp instead of adult shrimp?

Different species of shrimp behave instinctively. Young male shrimp fight against everybody including females of their own species because they are not ready to reproduce. When they get to be adults they fight against everybody except the females of their own species because now they want to attract the female and mate with her. If adults meet a female of another but very similar species they fight but less aggressively; if they meet a female of a more different species they fight more aggressively.

QMaybe I missed this on the show, but I didn't quite follow how the diversion of the Gulf Stream, following the development of the isthmus of Panama, caused man to begin to walk upright. Can you please explain? Thanks.

Many scientists think that the closure of the Isthmus of Panama strengthened the warm Gulf Stream Current. This current took warm waters high into northern latitudes providing moisture to the atmosphere so that snow formed to build the glaciers of the ice age. At the same time a strong current also flowed south along the eastern side of the Atlantic Ocean and affected the climate of north Africa causing it to become drier so that savannahs and open grasslands developed which provided the habitats that previously arboreal (tree living) primates then colonized. In the process they became more socially organized and started to walk upright.

QDo you feel that the formation of the Isthmus of Panama has anything to do with causing the phenomenon El-Nino?

The formation of a land barrier between the Atlantic (Caribbean) and the Pacific certainly changed the patterns of ocean circulation in both oceans. It is very likely that this change helped to set up the oceanic conditions in the eastern Pacific which allows the El Nino to develop every few years.

QI have always been taught that the Earth is approximately 4000-5000 years old. I was watching the show and you said that it took millions of years just to form Panama. How can you tell how long it took?

Some Christians (and perhaps other religions also) believe that the Earth was formed 4-5000 years ago. These dates are generally calculated from estimates interpreted from the Bible. Other Christians and especially many scientists do not believe that the Bible is a literal description of the origin of the earth, but more like a parable or story that uses the images and concepts that the writers of biblical times had long ago. Scientists try to measure the age of the earth by observing changes inside the minerals that form rocks and project from their observations the rate of these changes, so as to estimate how long the process has been going on. Using many different techniques there has grown a general agreement by many different geologists that the earth is very old by human standards, approximately four and a half thousand million years (4.5 billion years). If this is true there is plenty of time to take a few million years to form the isthmus of Panama. It is very important to understand that many Christians are also scientists and follow the estimates of scientists (based on direct observations and calculations) to try to understand the way that the world functions and how long is its history. Rather than take the Bible literally they believe that it is more reasonable to follow the scientific method to understand the world and its physical and chemical processes that you can measure and sense even while you may choose to believe that there is a God that created it all.

QIs the Smithsonian Tropical Research Institute open to visitors who are interested in touring the Island and seeing first-hand the fascinating research there? Are there any opportunities to volunteer for field work with you or other scientists?

The Smithsonian Research Institute is not open to the public in general except for its main offices in Panama City, Panama where there is an excellent library on tropical biology, geology and archeology as well as a gift shop with items of interest in Natural History (a small version of one of the Museum stores at the Smithsonian on the Mall in Washington). If you make arrangements with a local tour company there are visits to the tropical rain forest in Barro Colorado Nature Monument where you can see howler monkeys and many other animals that were seen on the program. Because of space and difficult logistics (All researchers and staff fill up the boat you have to take to Barro Colorado Island where the Smithsonian Lab is) public and tourist visits are not possible to the laboratories and research area. If you become a biology student though you may get to work there!

QOn this story it was mentioned that the animals that traveled south over the land bridge did better than the animals that traveled north. Can you please tell us why?

Yes some 50-60% of the animals of South America, including cats, deer, mice, bears, and many others were not known in South America until about 3 million years ago. Why there are only three species that remain from the migration from south to north is not known certainly. Many scientists think that because the North American animals had already evolved in competition with animals from Asia, which had crossed the Bering Land Bridge during the Ice Age and had then survived within North America, they were in some way "hardened" or more robust when they met and competed with the South American animals which had been isolated on that continent for millions of years and had never faced competition from other regions before. But this is just speculation.

QDid I hear correctly during the show on Panama that hedgehogs were among the animals present at the time the land bridge formed between North and South America? I did not know that hedgehogs had ever been present in America. I had thought they were only found in Africa, Europe and Asia. If they were present in America, could you provide some information about them (when were they present in America, what were they like, and when and why did they disappear, etc.).

This is a perceptive question. It is true that strict hedgehogs which mostly belong to the genus Erinaceus, are known only in the old world. Porcupines, which are a different family but have the same strategy of spiny skins that can roll up into a ball for protection when attacked, are known in both the old and new worlds. But the dictionary also defines hedgehog as referring to any similar spiny mammal which is the sense in which I used it (I was quoting from the articles on the Great American Biotic Interchange by David Webb) But the questioner is strictly speaking correct and I would have been more accurate to have referred to porcupines.

QWho first came up with idea of making the canal? About how many miles long is the canal from Panama City to the Caribbean Sea? About how long does it take for a boat to travel all the way through the canal?

The idea of a canal across the Central American Isthmus is quite old historically. The Spanish early in their conquest wrote about the possibility, the British surveyed the San Juan River between Costa Rica and Nicaragua and the route over to the Pacific I believe in the early 19th century or latest 18th century, and of course the French started to build the canal in Panama in the late 1800s but failed. Their route was successfully taken over by the USA and the canal was completed by 1914.

It is about 65-70 kilometers as the crow flies from Panama City (the Pacific entrance to the canal) to Colon (where the canal reaches theCaribbean). Ships usually allow about 24 hours to complete the crossing of the canal of which about 10-12 is spent navigating the canal and its locks and the remainder at anchor with other ships waiting their turn to be called by the Panama Canal Commission that a pilot is ready to take them through. The Canal is the only place in the world where the pilot takes complete control of the vessel and the captain cannot countermand him.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.