Philosophers wrestling with the big questions of life are no longer alone. Now scientists are struggling to define life as they manipulate it, look for it on other planets, and even create it in test tubes.
In June, researchers replaced the genetic identity of one bacterium with that of a second microbe. Other scientists are trying to build life from scratch. NASA scientists are searching for life in space but aren't sure what it will look like. And some futurists are pondering the prospect of robots becoming so human they might be considered a form of life.
So as scientists push the bounds of biology, astronomy and robotics, a big question looms: What exactly is life?
That question is bubbling up from recent advances in lab work.
In suburban Washington this summer, prominent scientists at the J. Craig Venter Institute, who were key players in mapping the human genome, switched DNA from one bacterium into another, changing its genetic identity. That put the world on notice that man's ability to manipulate life is dancing around the point of creation.
Now Venter is asking for a patent for a completely new bacteria that would be created by inserting genes into a hollowed-out cell of what once was a urinary tract bug. Venter doesn't view that as creating life, just "modifying life to come up with new life forms."
At least half a dozen other research teams around the world are going farther, trying to create life out of chemicals, mimicking the beginnings of life on Earth. They're somewhere from three to 10 years from success, they figure.
For them, and Venter, new man-made life forms mean new energy sources, environmental clean-up mechanisms and life-saving medicines. For others, such a breakthrough would mean understanding how life began on Earth by trying to recreate it.
"We're all sort of thinking that the next origin of life will be in somebody's lab," said David Deamer, a University of California, Santa Cruz, biochemistry professor who is one of the leading experts trying to create life. But ask Deamer what life is, and he responds by saying it's best to describe it, not define it.
Broadly put, scientists like Deamer say life requires a cell with genetic material and the ability to reproduce, turn food into energy, and to evolve through natural selection. But it's not that simple for others seeking a definition.
At NASA's Astrobiology Institute in California, which studies extreme life here and the possibility of it elsewhere, it's far easier to say what life isn't, said institute director Carl Pilcher.
"Right now we may not have the base of knowledge necessary to answer the question, but there are ways we are proceeding," he said.
Last month, the National Academy of Sciences issued a "weird life" report cautioning NASA not to be so focused on water. It told the space agency that "as the search for life in the solar system expands, it is important to know what exactly to search for."
That same report urged NASA to avoid being "fixated on carbon" when it looks for life even though carbon is often called the backbone of life on Earth.
But if carbon isn't a requirement for life, how about silicon? In other words, what about machines?
Ray Kurzweil, a renowned futurist who advises people such as Bill Gates, believes that by 2029 a machine will pass a prime test of artificial intelligence, offering the same kind of answers as a human.