Looks like this masked booby, a Pacific sea bird, is expecting manna from heaven. In reality, this "skypointing" is part of the mating ritual.
evolve, you evolve, they evolve
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?
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.
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.
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.
are 1 2 3 4
5 pages in this feature.
Bibliography | Credits | Feedback | Search