Pacific Views

The Evolution of Evolution

It isn't that Charles Darwin just took a long cruise on the Beagle, and the theory of evolution miraculously popped into his head. Evolution, like many great ideas, had an intellectual history that was the natural product of its time. In fact, if it weren't for a letter sent to Darwin in 1858, we might all be talking about Wallace's theory of natural selection.

Via colonialism and empire-building, European museums in Darwin's age were the most fashionably stocked trophy galleries ever. Educated explorers and civil servants from a handful of cultures had access to the farthest corners of the Earth, and they added their souvenirs to the stockpile. Available to European scientists of the day was more information about more parts of the planet than gathered together previously. Geology, archeaology, and the study of living things began to shape up as serious disciplines. With all these facts at hand, it was inevitable that someone would start doing some thinking.

Curiously, some of the ideas most crucial to forming the thory of evolution came from geology. The geologist James Hutton first put forth the idea of gradualism. Looking at the natural features of the Earth's surface, Hutton's theory was that geographic variety was the result of the same processes we see around us today operating over long periods of time. Slowly, a river can cut a canyon through rock, rain can wash land into the sea, sediment can be compressed back into rock.

Charles Lyell refined Hutton's theory into what was known as uniformitarianism. That is, he said that not only were geological features formed by ordinary and ongoing processes, but they happened at constant rates. That they had been operating over a long span of time, slowly making mountains and eroding them down at a steady crawl that was barely perceptible to short-lived humans.

Both Hutton and Lyell saw that even a small rate of change, if continuous, can produce dramatic results. And looking at the dramatic results of geological processes, it was suspected that the planet was much older than 6000 years.

Around the turn of the 19th century, evolutionary origin theories were becoming more popular. Naturalists thought about this 'newly' old Earth, and began to wonder if change through gradual processes over a long span of time were as applicable to living things as to rock. The most complete pre-Darwinian theory of evolution was put forward by Jean Baptiste Lamarck, who kept the invertebrate collection at the Paris Natural History Museum. It seemed to Lamarck that the modern animals looked to be the descendants of related families of animals in the fossil collection of the museum who had, over time, become more complex and better adapted to their environments.

The mechanisms Lamarck suggested for the gradual change of forms goes against everything we know about inheritance today, though his general conclusions hit closer to the mark than any other theories up to that point. Ironically, the same misconceptions are still with us, and are probably more widely believed to explain evolution than Darwinian inheritance.

The two main points where he went wrong came from looking as evolution as something that happens to an individual organism. But unless you're talking about bacterial gene transfer (and he wasn't), evolution doesn't happen to individuals, only to species. Lamarck thought that evolution proceeded in part because of the needs and intent of a living organism, and he thought that inheritance proceeded by passing on traits acquired during a lifetime. Neither guess was correct, but that's a discussion for another time.

Before becoming history's most controversial scientist, Darwin was an accomplished naturalist who had originally intended to go into the clergy. He closely observed and wrote about thousands of organisms, collecting numerous specimens in his travels. He came to wonder why species of plants or animals in one area resembled each other more than they resembled plants or animals with similar functions somewhere else in the world. He saw species that existed nowhere else in the world but the tiny Galapagos Islands, and he got to wondering why.

To his enduring good fortune, he'd brought Charles Lyell's writings with him on his travels. Given the idea of a planet that was far older than biblical literalism suggested, and that it had been changing steadily all that time, Darwin began to wonder if this explained the variety of species all around us.

Darwin returned to Britain in 1836, and had the crucial insight that evolution was related to a species' adaptation to its environment over time. He hypothesized that if members of the same species became isolated from each other in different environments, that over a long period of time, they would become so different from each other as to be separate species. For years, he gathered more information and refined his ideas, while corresponding and speaking extensively with other scientists.

Among them, Charles Lyell, whose book on geologic change had made such an impression on him. Lyell urged Darwin to publish before someone else beat him to it, but Darwin resisted. Then in 1858, a young naturalist named Alfred Wallace wrote a fateful letter to Darwin asking the distinguished man to review his own theory of natural selection and let him know if it was worth publishing. The similarities were so strong that in a letter to Lyell, Darwin wrote, "Your words have come true with a vengeance... I never saw a more striking coincidence ... so all my originality, whatever it may amount to, will be smashed."

Darwin rushed to get a paper ready for publication, and his work was published together with Wallace's the following month. Darwin's notes of the 15 previous years, and the greater depth of his argument, gained him the lion's share of the recognition. He published The Origin of Species the very next year, in 1959.

It took only a decade for Darwin's wealth of evidence and clear argument to convince a majority of the life sciences community that natural selection was the cause of the diversity of species. As for the rest of the world, well we're still working on that.

- This post makes shameless and extensive reference to material from Chapter 22 of "Biology: Fifth Edition" by Campbell, Neil A.; Reece, Jane B.; and Mitchell; Lawrence G. Copyright 1999, by Benjamin/Cummings, an imprint of Addison Wesley Longman, Inc. Any understanding of the material on my part is thanks to the tireless efforts of my professors.

Posted by natasha at November 26, 2004 06:43 AM | Science | Technorati links |