Everything Everywhere Daily: History, Science, Geography & More - Darwin's Other Theory

Episode Date: March 5, 2021

From December 27, 1831, to October 2, 1836, the HMS Beagle set out on a scientific survey expedition in the Atlantic and Pacific Oceans. On the ship was a young man named Charles Darwin. That expedition exposed him to ideas that would develop his theory of natural selection which would revolutionize the world of biology. This episode is not about that theory, however. This is about his OTHER theory that he developed from that expedition. Learn more about your ad choices. Visit megaphone.fm/adchoices

From December 1831 to October 1836, the HMS Beagle set out on a scientific expedition in the Atlantic and Pacific Oceans. On the ship was a young man named Charles Darwin. That expedition exposed him to ideas that would develop his theory of natural selection, which would revolutionize the world of biology. This episode is not about that theory, however. This is about his other theory that he developed from that expedition. Learn more about Darwin's theory on the development of coral atolls, on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong?

ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. This episode is sponsored by the Travel Photography Academy. In 2007, I sold my home to travel around the world. I bought an expensive camera that I didn't know how to use

and took a bunch of terrible photos. Several years, 100 countries, and tens of thousands of photos later, I'd improved my photography to the point where I was winning national awards being named Travel Photographer of the Year three times in North America. I created the Travel Photography Academy so you don't have to spend the many years that I did

to improve your photography. Even though we can't easily travel right now, you can still work on improving your photography at home and in your own community. Just go to travel photography academy.com or click on the link in the show notes to start improving your photography today. The second voyage of the HMS Beagle was one of the most profound in the history of science. Originally, the ship was set out on a two-year expedition to improve nautical maps around South America. With the independence of Argentina and Chile and the opening of trade with these countries, the British needed proper maps for their ships.

One of the big components of the expedition was determining the longitude of various places around South America. They took 22 clocks with them, which is how they would measure longitude. I briefly talked about this on my history of timekeeping episode, and I'll probably do a future episode on Longitude, and how that problem was solved. One of the passengers on the ship was a young 22-year-old named Charles Darwin. He was on the ship in the role of a naturalist and a biologist, as the captain of the ship thought it would be useful to have such a person on board. The two-year voyage of the HMS Beagle turned into a five-year voyage. The initial investigation of the waters around South America expanded into visiting many of the islands in the Pacific, New Zealand, Australia, and eventually circumnavigating the globe. During the expedition,

Darwin actually spent three of the five years on land, taking notes, finding fossils, and making observations about the zoology he encountered along the way. The result of his observations was on the origin of species, perhaps the most revolutionary book in the history of biology. The book was published in 1859, 23 years after the HMS Beagle completed its journey. However, before he published that, he published something else. As part of the expedition, the British Navy asked Darwin to investigate and map coral atolls. The Navy had a vested interest in knowing more about atolls given the threat they pose to ships. Attolls are circular islands made up of sand and ringed with coral reefs.

Coral reefs are extremely dangerous to ships, especially wooden ships. They often lie just below the water line and can devastate wooden ship hulls, and they would often appear out of nowhere in the middle of the ocean. During the voyage and in between a study of birds and other wildlife, Darwin made observations and maps of all of the coral reefs he encountered. His maps of atolls were really good. Many oceanographers have commented on how they could still be used today as they were so accurate. Darwin noticed that there were roughly three types of coral reefs, fringe reefs, barrier reefs, and atolls.

Fringe reefs are where coral is right next to the beach. You could literally step or swim not far from the beach, and coral would be right there. Many of the reefs in the Caribbean are fringe reefs. A barrier reef is similar in composition to a fringe reef, but they're further out from shore. There is some sort of space between the reef and the mainland. A barrier reef can sometimes surround an island with a lagoon inside. Finally, there are atolls. As I mentioned, atolls tend to be roughly circular in shape with thin, narrow islands.

They don't stick out much over the water and usually have a high point of no more than a meter above sea level. Fun fact, there are four countries in the world that are made entirely of coral atolls, the Maldives, the Marshall Islands, Kiribas, and Tuvalu. Darwin's ideas were published in a paper in 1842, titled, The Structure and Distribution of Coral Reefs being the first part of the geology of the Beagle under the command of Captain Fitzroy Royal Navy during the years 1832 to 1836. That was quite a mouthful for a title. Darwin noticed that there seems to be a progression in the way that reefs formed around islands.

Let's take, for example, the Hawaiian Islands, which was not visited by Darwin on his voyage, but it makes for a good example. The big island doesn't have much in the way of reefs. What reefs they do have are close to shore on the western side of the island where there is an active volcanism. It's also the largest, tallest, and newest of the Hawaiian islands.

The next island over is Maui. It's not as big as the big island and not quite as tall, but it's a little bit older and the coral is more developed. It sort of continues in this fashion as you go west down the chain of islands. Each island is a bit smaller,

a bit older, and has better formed reefs. The Hawaiian islands, however, don't stop with the populated islands. They keep going for a thousand miles past the last populated Hawaiian island. As you keep going, the islands become smaller, the coral becomes more pronounced, until they become full coral atolls with no island in the middle, all the way out to Midway Island. Darwin theorized that the islands were created by volcanoes, like the Big Island.

Then, over millions of years, they eroded and subsided back into the ocean. all why the coral kept growing around the island. In the end, you're left with a ring the shape of an island, but eventually with no island in the middle. Darwin also took more observations on water temperature and latitude, which puts limits on where coral could thrive and explain why they're only found in the tropics. Darwin had been sending back reports from the expedition

for the entire time of the voyage. By the time he arrived back in England, he was a bit of a celebrity in scientific circles. The reason for the excitement was his theory of course, coral atoll formation, not anything to do with natural selection at this point. If you had asked most scientists in mid-19th century England about Charles Darwin, they would probably have known him best as a geologist. His theory of coral atoll formation has been taught in universities for decades. Darwin's theory is simple, beautiful, and elegant. However, it also might be incomplete. In the last

few years, there are some geologists who have begun to question Darwin's atoll theory. There's just a lot that Darwin didn't know about geology, which has been learned over the past 190 years, information about plate tectonics, ice ages, and most importantly, changes in the sea level. These other scientists have a theory which holds that atolls are actually created due to the rise and fall of the sea. Over hundreds of thousands of years, sea levels would rise and fall, and the reefs would rise and fall with them as coral would grow when sea levels rose, and then erode back when the sea levels fell. That being said, Darwin's model is, as of now, the dominant model being taught in schools for the formation of coral atolls.

So the next time you hear someone mention something being Darwinian, ask them exactly what they mean and what it has to do with the formation of coral atolls. The associate producer of Everything Everywhere Daily is Thor Thompson. If you'd like to support the show, please donate over at patreon.com. There is content only available to supporters, merchandise, and even opportunities for a show producer credit. If you know someone you think would enjoy the show, please share it with them. Also remember, if you leave a five-star review, I'll read your review on the show.