All of science owes debt to Darwin

Sunday, February 8, 2009

The shy young naturalist Charles Darwin, who voyaged around the world aboard HMS Beagle and became the bearded sage of rational scientific thought, is having a birthday this week – his 200th – and celebrations have already begun throughout the Bay Area, and indeed on every continent.

“No one,” says Kevin Padian, a Berkeley biologist and tracker of dinosaur evolution, “has influenced modern thought, modern science, and indeed our modern culture more than Darwin.

“His influence is everywhere, and science would be impossible without him.”

Every true scientist at work today is in fact a Darwinian.

They are decoders of the human genome, immunologists battling AIDS, stem cell researchers seeking tomorrow’s cures, anthropologists unearthing fossil hominids to define our human ancestry – even the “astrobiologists” seeking life on other planets while they study organisms living in extreme conditions on Earth.

The man who was born just 200 years ago Thursday did not stumble on his theory of natural selection in one blinding insight – as legends that have morphed into quasi-history would have it – when he observed the varied finches and mockingbirds and tortoises of the Galapagos Islands during the Beagle’s stopover there.

charles_darwin_01

No, his theories developed long after the observations he had made while adventurously collecting fossils of long-extinct beasts and living plants and animals – largely in South America.

His first insights on evolution and the emergence of new species came to him two years after the Beagle returned to England, and it wasn’t until 1859, more than 20 years later, that Darwin, inspired by the writings of Thomas Malthus on population pressures and Charles Lyell on the ancient age of Earth’s geology, completed his first great work: “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.”

To evolution researchers today, the California Academy of Sciences in San Francisco is an important source of information, for the academy maintains the world’s largest collection of Galapagos plant, animal and insect life. The Galapagos archipelago and the Darwin Research Station in the tourist-jammed town of Puerto Ayora on the island of Santa Cruz there remain an international monument to his achievement.

Collecting specimens

Darwin, no ornithologist, had collected scores of finches and mockingbirds from different Galapagos islands and noticed how widely varied the finch beaks were. He thought some were not finches at all.

But it was long after the Beagle’s return to England that he learned his birds were of widely different species and wondered how they came to be.

“One might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends,” he wrote in “The Voyage of the Beagle.”

Descent from common ancestors with modification are watchwords for scientists of all stripes today. And Darwin saw more clearly than anyone that the pressure for modification came primarily through natural selection: Beasts or plants or microbes come from common ancestors. They are modified to adapt best to an environment, and produce descendents; those who aren’t adapted die by the wayside – just as the Neanderthal people may have died away competing in vain with the first Homo sapiens, our direct ancestors. That’s today’s version.

Species adaptation

“A steady thread of Darwin’s natural selection runs through all our work,” says David Mindell, dean of science and curator of ornithology at the California Academy of Sciences in Golden Gate Park who studies the evolution of predatory birds – hawks, eagles, falcons and the like. “Darwin has given us the way to see how species change over time, how new species arise – and that fact remains the real focus of all scientists who study evolution.”

The concepts of natural selection and Darwin’s later parallel discovery of sexual selection operate at all levels of life, and not just among vertebrate animals that reproduce sexually, Mindell says.

“You can put a culture of bacteria into a laboratory flask, and even though they reproduce by fission, you can see natural selection operating even there – new bacterial species will arise almost instantaneously,” he says.

Among his own birds of prey, as Mindell notes, Darwin’s concept of sexual selection operates clearly: A bird uses its plumage – or its chirps or raucous cries and whistles – to signal to a potential mate that it has the most desirable genes for producing the best descendants. To Mindell, that means that studying “molecular systematics,” or the structure and sequences of genes in his birds, can lead to clues to the evolution of new species.

They are, Mindell says, “molecular clocks” for the history of speciation.

Intelligent design

Padian, the Berkeley biologist, testified as an expert witness during the famed 2005 trial in Dover, Pa., over the school district’s decision to order the teaching of intelligent design as an alternative to evolution in explaining the origin of life. Intelligent design is based on the idea that living organisms are too complex to have evolved naturally, and must have required an intelligent designer to create them.

Like virtually all scientists today, Padian equates intelligent design with biblical creationism, a view held also by the judge in the Dover case who ruled that intelligent design “is a religious view, a mere re-labeling of creationism, and not a scientific theory.” In Dover, evolution won.

Despite that ruling, efforts to promote intelligent design continue to roil school districts across America, and Darwin’s evolution – no more a theory than gravity or the round Earth – is still under legal assault.

Padian is a foremost expert on the evolution of dinosaurs, the creatures that ruled the earth for about 160 million years and whose mass extinction an estimated 65 million years ago has given rise to conflicting causes: a meteorite crashing onto Earth or Indian volcanoes erupting in catastrophe.

To Padian, however, the dinosaurs never really went extinct. His studies, and those of many others, have provided overwhelming evidence that dinosaurs evolved in true Darwinian fashion to become today’s birds.

Some of the meat-eating fossil dinosaurs that Padian and other scientists have unearthed at ancient sites around the world bore fierce horns, while their more placid plant-eating relatives did not. So Padian today is also studying the evolution of horns in modern animals.

“That’s why,” he said recently, “I studied a thousand skulls of different antelope species in South Africa – to see how they fit into Darwin’s tree of life.”

 

E-mail David Perlman at dperlman@sfchronicle.com.

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