Remembering Charles Darwin: the evolution guru

Posted: February 13, 2011 in Articles, Other collections

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Charles Robert Darwin FRS (12 February 1809 – 19 April 1882)

Today biologists are exploring evolution at a level of detail far beyond what Darwin could, and they’re discovering that evolution sometimes works in ways the celebrated naturalist never imagined. "The biological problems we’re dealing with are much more complex," says Massimo Pigliucci, an evolutionary biologist at Stony Brook University in New York. "That said, it’s a lot of fun. I’m not complaining."

Darwin developed his theory by gathering as much information as he could about life. He collected it while voyaging on the Beagle, by sitting in front of a microscope back in England and by writing to a global network of correspondents. Today, however, biologists can feast on a far bigger banquet of data. The fossil record was scanty in Darwin’s day, but now it has pushed the evidence of life on Earth back to at least 3.4 billion years ago. And while Darwin recognized that variation and heredity were the twin engines that made evolution possible, he didn’t know what made them possible. It would take almost a century after the publication of On the Origin of Species for biologists to determine that the answer was DNA.

DNA is like a genetic cookbook, using four molecular "letters" to spell out recipes for everything from hormones to heart valves. Biologists today are reading the 3.5 billion letters in the human genome as well as the DNA from thousands of other species, and they’ve amassed vast databases of genetic information that they can rummage through to learn about how life evolved.

Time and again, biologists are finding that Darwin had it right: evolution is the best way to explain the patterns of nature. "You just can’t even start to make sense of all this data without a framework of evolution," says Günter Wagner, an evolutionary biologist at Yale University.

Darwin proposed that natural selection could gradually transform a species.Now biologists are applying DNA-sequencing technology to natural selection, which lets them identify the individual genetic changes that boost reproductive success.As populations adapt to their surroundings, they can gradually evolve into new species. "We now have, I think, a good understanding of how new species arise — that is, how biological diversity is created," says Jerry Coyne, an evolutionary biologist at the University of Chicago. Biologists have also found plenty of evidence to support Darwin’s other major claim: that different species share a common ancestry. Over the past 15 years, for example, paleontologists have found several fossils of whales with legs, linking modern whales to their terrestrial ancestors. Besides studying fossils, biologists can discover the genealogy of species by looking at their DNA. The fossil record points to hippos and other hoofed mammals as being the closest living relatives of whales.

 

It’s been 1.5 billion years or more since our ancestors split off from our fungal cousins. How did the genome of our ancestor change so that it could produce two-legged primates? One part of the answer is that mutations over time altered genes that encode proteins, and some of those changes have been favored by natural selection. But that does not mean that our genome — the sum total of our human DNA — is a finely tuned collection of protein-coding genes. In fact, a lot of mutations that all humans carry neither helped nor harmed our ancestors. They spread just by chance. And a lot of our genome is not made up of protein-coding genes. In fact, 98.8% of it is not. Some of that 98.8% consists of "pseudogenes" — genes that once encoded proteins but no longer can because of a crippling mutation. They are the molecular equivalent of a vestigial tail, allowing us to see evolution’s track.

Biologists are a long way from understanding the entire genome, but as they get to know its parts better, they’re getting a more precise comprehension of one of the most important features of evolution: how complex organs evolve, that the new complex organs could evolve through a series of intermediate forms.

Nevertheless, new traits have evolved. Once there were no brains, and now there are billions. Once you could search the entire world and never find a leaf. Now the world is green. Biologists are discovering some of the genetic secrets for evolving new traits. One is to recycle old genes.Darwin had no way of knowing this, since he had no way of examining DNA. If he did, he might well have rethought one of his most potent metaphors for evolution: the tree of life. It’s not that the metaphor is wrong.

But there’s more to the history of life than the branching of a tree. Every now and then, DNA moves between species. Viruses ferry genes from one host to another. Bacteria swap genes inside our bodies, evolving resistance to antibiotics in our own gut. Some 2 billion years ago, one of our single-celled ancestors took in an oxygen-consuming bacterium. That microbe became the thousands of tiny sacs found in each of our cells today, known as mitochondria, that let us breathe oxygen. When genes move this way, it’s as if two branches of the tree of life are being grafted together.

Darwin predicted this. "We can dimly foresee that there will be a considerable revolution in natural history," he wrote at the end of On the Origin of Species. He saw his work not as the end of biology but as a beginning.

Putting Evolution to The Test. How does Darwin hold up?

Darwin’s microscope. His research, given the technology, was robust.

 

on his 202nd Birthday and 152nd year of The Origin of species!

(scraps from an old article of Time magazine)

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