200 Years After Darwin's Birth, Scientists Are Decoding the History of Human Evolution
Thursday, February 12, 2009
In biology's most famous book, "On the Origin of Species," Charles Darwin steered clear of applying his revolutionary theory of evolution to the species of greatest interest to his readers -- their own.
He couldn't avoid it forever, of course. He eventually wrote another tome nearly as famous, "The Descent of Man." But he knew in 1859, when "Species" was published, that to jump right into a description of how human beings had tussled with the environment and one another over eons, changing their appearance, capabilities and behavior in the process, would be hard for people to accept. Better to stick with birds and barnacles.
Darwin was born 200 years ago today. "On the Origin of Species" will be 150 years old in a few months. There's no such reluctance now.
The search for signs of natural selection in human beings has just begun. It will ultimately be as revelatory as Newton's description of the mathematics of motion 322 years ago, or the unlocking of the atom's secrets that began in the late 1800s.
The inundation of data since the completion of the Human Genome Project in 2003, and the capacity to analyze it at the finest level of detail -- the individual DNA nucleotides that make up the molecule of heredity -- are giving us a look at humanity's autobiography in a way that was once unimaginable.
In small, discrete changes in our genes that have accumulated over time, we are seeing evolution's tracery, as durable as it is delicate. It is slowly revealing how climate, geography, disease, culture and chance sculpted Homo sapiens into the unique and diverse species it is today.
Biologists are discovering that the size of our limbs and brains, the enzymes in our spit and stomachs, the color of our skin, the contour of our hair, and the armament of our immune systems are each to some degree the products of evolutionary adaptation. They are the hard-earned, but unintended, bequests of our ancestors' struggle to survive.
This, of course, is no surprise. Darwin knew it was so -- and he'd never heard of a gene.
The surprise is our capacity to see the mechanical changes -- for genes are nothing more than little machines operating in water -- that are evolution's working material. Natural selection has moved beyond metaphor. We can see the thing itself.
"Why are we the way we are? That has always been a sort of fundamental question, hasn't it? But it is only now that we can really begin to address it," said Carlos D. Bustamante, a professor of computational biology at Cornell University. "Over the ages we catalogued the anatomical differences between people and eventually biochemical differences, too. Now we can get down to the molecular differences. We really mean it this time."
Understanding which of our 25,000 genes have changed since we climbed out of the trees may have practical results as well. Many of mankind's most common health problems -- hypertension, diabetes and obesity are examples -- may partly be consequences of natural selection that occurred long ago, in a world far different from today's. Identifying which genes have undergone the most rapid evolution, and then figuring out what they do, may shed important light on these ailments.
Out of this research may come one other tantalizing insight: How, if at all, are we still evolving?