Monday, January 19, 2009

Evolution's Evolution

In this article from Science News, the authors essentially offer a review of the idea that evolution has evolved over the years. Obviously, it has, with new ideas and new areas of study emerging over time.
Darwin’s dangerous idea has adapted to modern biology

Just a decade after he published On the Origin of Species, Charles Darwin was already worrying about the evolution of his idea. In an 1869 letter to botanist Joseph Dalton Hooker, Darwin lamented:

“If I lived twenty more years and was able to work, how I should have to modify the Origin, and how much the views on all points will have to be modified! Well, it is a beginning, and that is something.”

Calling the Origin a mere “beginning” is like saying the Beatles were just a rock band or that Shakespeare wrote some decent plays. Darwin’s gifts to science were radical. He not only proposed that all of Earth’s diverse beings shared a common ancestry, but also described an elegant mechanism to explain how all that diverse life came to be. Darwin was a master of merging data from different disciplines, pain-stakingly drawing from zoology, botany, geology and paleontology to build a solid foundation for evolutionary biology. Today, 150 years later, scientists continue to grapple with ideas descended from that foundation. Still, Darwin’s central tenets survive, fit enough to frame the questions posed by modern biology.

“He had great intuition,” says Yale University’s Michael Donoghue. “He’s the guy we all envy.”

Darwin’s powers of observation and reason extended from microflora to megafauna; he could see the whole forest while scrutinizing the branches on the trees. His ideas illuminated life’s development in the Earth’s deep past and foreshadowed many scientific developments that would come in the future, including the modifications and refinements to his theory that scientists are still exploring. Yet, were Darwin alive today, his head might spin at the complexities entangling the expansion of his original ideas.

Evolutionary theory is not a well-preserved fossil in a dusty museum, but a thriving field of study pursued at lab benches, on beaches and in bogs. The exploding research program known as “evo-devo,” for instance, has wed evolutionary theory to embryology and genetics, helping to unravel the evolution of organisms’ structures and forms. Scientists are also reformulating ideas about evolution’s pace, showing that

Darwin’s idea that change happens gradually and incrementally doesn’t always capture the whole story. Researchers are fleshing out Darwin’s central idea of natural selection — discovering when it’s the driver and when it takes a back seat. And along with investigating how selection operates on organisms — Darwin’s unit of choice — scientists are also showing how it acts on groups, genes and behavior. Experts are still debating the very definition of a species.

If Darwin came back, “in some ways he would be mystified,” says evolutionary biologist Douglas Futuyma of Stony Brook University in New York. “Evolutionary biology has been radically changed — and deeply enriched.”

The ‘dangerous idea’ Of course, Darwin was familiar with radical change. In his day most biologists (or “naturalists,” then) believed that each species was individually created and forever immutable. But during his travels in the 1830s on her majesty’s ship the Beagle, Darwin saw plants and animals and fossils — and distributions of all three — that just didn’t square with the idea that species don’t change.

“It was evident that such facts as these, as well as many others, could only be explained on the supposition that species gradually become modified; and the subject haunted me,” he noted in his autobiography.

Upon his return to England, Darwin pored over his notes and “collected facts.” Eventually he accepted the unacceptable and wrote, in 1844, to his friend Hooker: “At last gleams of light have come and I am almost convinced (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable.”

That year Darwin penned his idea in a manuscript that remained unknown to the public until portions of it were presented to the Linnean Society in 1858. Subversive as it was, Darwin’s proposal that species can change was not the first. Naturalists and philosophers had long been contemplating life’s diversity. By the late 1700s, French naturalist Georges Cuvier had established that after great environmental change, some organisms got snuffed out, went kaput, extinct. A little later, zoologist and philosopher Jean Baptiste Lamarck proposed the notion of adaptation, explaining variation among organisms as a response to their environments. But Lamarck saw the change in organisms through time as a one-way path to perfection, from simple to increasingly complex, with humans at the pinnacle. His environment-caused variation was an excuse to explain why some organisms strayed from the “tendency toward perfection.”

It took Darwin and Alfred Russel Wallace to recognize (independently) that variety was actually the spice of life, not its flaw. Both men had read the work of economist Thomas Malthus, who warned that food supplies could never keep up with growing populations. No matter what, some people would meet an early death. Darwin and Wallace both reasoned that beetles, birds and beech trees also have more babies than can survive and that variation among such offspring was important in determining who lived. Individuals who were better equipped for their environment than their siblings or neighbors would survive; the features that enabled their survival would be passed on to their kids.

Darwin called this process natural selection, and life evolved largely because of it, he argued in the Origin. (The word evolved appeared only once, the last word on the Origin’s last page: “from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”) Evolution via natural selection, Darwin believed, could yield both life’s incredible diversity and its striking similarities.

Those similarities are repeatedly and presciently remarked upon by Darwin, who called morphology — the study of form — “the most interesting department of natural history, and may be said to be its very soul.” In the Origin he writes: “What can be more curious that the hand of a man, formed for grasping, that of a mole for digging, the leg of a horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?”

But only in recent years have evolution and embryology become integrated into a flourishing field dubbed “evo-devo,” for evolutionary development, a research program investigating how bodies — their size, shape, color and different parts — evolve.

Read the rest of the article.

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