Treasures of Evolution Island
   

side titlesEvolution islandsProtests at GalápagosScientific bonanzaMocking the finchesHuman side of discovery


Birds will go to great lengths to get recognized by the ladies. This frigate bird blows up for courtship purposes.
All original photos this page copyright and courtesy Robert Rothman

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Looks like this masked booby, a Pacific sea bird, is expecting manna from heaven. In reality, this "skypointing" is part of the mating ritual.

   

I evolve, you evolve, they evolve
Charles Darwin's theory of evolution is premised on variations in the characteristics (say, size, tooth length or sense of smell) of individual members of a species. As each organism is tested by its environment, the number of its offspring depends on the fitness to survive conferred by those characteristics.

It looks obscene, a bright red sac hanging from the throat, but that's apparently the frigate bird style.If, for example, you can smell predators from a longer distance, you'll out-live animals with a stunted sense of smell.

Gradually, species change in response to the environment as the losers are culled and the winners have more young which perpetuate those winning characteristics.

The crux of natural selection, says Robert Rothman, a professor of biology at Rochester Institute of Technology, is that the young "must survive to reproduce more effectively than their neighbors." The Galápagos masked booby, he points out, can only support one chick per season, and natural selection "operates to determine which juveniles survive." A variant better able to survive -- say if it's more tolerant of starvation while its parents are fishing at sea -- is more likely to survive and produce starvation-tolerant offspring. While evolution governs change, the results are unpredictable. Experiments on guppies by John Endler have shown that if many predators are around, drab, camouflaged male fish may have an advantage. Being more elusive, they survive long enough to breed. But if predators are rare, colorful guys may have more young because females prefer best-dressed mates -- if they happen to be alive.

Nature, in other words, uses "natural selection" to choose the winners in a process that, as Darwin noted, is analogous to the "artificial selection" that farmers use to breed better pigs or potatoes.

While it's called the "theory of evolution," Darwinism is a bedrock of biology -- the organizing principle behind the incredible wealth of life on Earth. Indeed "theory" has a different meaning in scientific and popular lingo, says Rothman, who teaches about the role of the Galápagos in natural history and evolution. "You have a 'theory' about who won the election, or whether OJ did commit the murder. But a scientific theory is much more complex; there's a rich body of research pointing to the accuracy of your theory." Interested in the creationism-evolution conundrum?A white bird with black wingtips and black beard has wings raised, meeting above its back. It's yellow bill aims toward the sky.

Changing Earth
Although Darwin had not formulated his theory of evolution by natural selection by the time he explored the Galápagos archipelago in 1836, he had already made many essential observations, and formed many crucial questions.

He believed, for example, that earth changes over time, as geologist Charles Lyell was maintaining. Darwin, who read Lyell's Principles of Geology in his deck chair on the Beagle, also directly observed that South America was rising from the ocean. He was already in Chile when a giant earthquake destroyed the city of Concepcion. As Darwin wrote, "The town of Concepcion is now nothing more than piles and lines of bricks, tiles and timbers-- it is absolutely true there is not one house left habitable."

Rothman, who takes students to the Galápagos every year, says Darwin then "found rocks that had recently been in the water, with barnacles, and they were 6 feet above sea level. Darwin put two and two together" and realized that quakes probably accounted for the raised beaches he'd seen in Patagonia. They were, he concluded, ancient shorelines that dried out when the land was raised.

Darwin was an avid student of geology, and the earthquakes told him that Earth's seeming stability masks continual change. How would plants and animals withstand these slow changes?

There were other clues that undermined a biology based on static species.

Darwin knew that:

plants and animals vary by location. South American cowboys told him a relative of the rhea -- a South American ostrich -- lived in Tierra del Fuego, the continent's volcanic southern tip. Darwin apparently forgot until a dinner featuring that bird, now named Rhea darwinii. As Rothman recounts it, after the rhea was half-devoured, Darwin "realized and recovered the remains of the meal" for shipment to England and scientific examination. We Why Filers figure that the incident proves that good science requires good eating...

organisms change through time. Fossils related to sloths and armadillos were found in places where similar animals were still living.

island animals are similar -- but not identical -- to animals on nearby mainlands. The Falklands fox, for example, a species (now extinct) found on those South Atlantic islands, resembled a fox on the mainland.

By the time he got to the Galápagos, Darwin was primed to absorb lessons from the simplified island ecosystem. Once there, he was forced to ponder the assemblage of animals he found -- where things looked familiar, but not identical, to what he'd seen in South America. a blue-footed booby

The Galápagos, he knew, arose as volcanoes that emerged from the ocean. From his own experiments on plant dispersion, Darwin knew some organisms could travel across the ocean. But, as Rothman notes, the logic of the Galápagos was suggestive: How could a relatively young island have life forms that were similar, but not identical to, continental forms? Since the islands were volcanic, they could not have been present at the creation, so the plants and animals living there had to have come from elsewhere. But they lived nowhere else. Therefore their ancestors came from elsewhere, and then changed into the present forms.

Darwin learned much at the Galápagos -- but "Darwin's finches" don't deserve much credit.

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