|Panel of scientists debate on “What is Life?”|
Sometime between 4 and 3.5 billion years ago, the emergence of life had intense beginnings on a young planet in the midst of a so-called primordial soup—consisting of water vapor, carbon monoxide, carbon dioxide, nitrogen, and ammonia and shaped by strong winds, electrical storms, volcanic eruptions, and ultraviolet radiation.
In 1953, Stanley Miller and Harold Urey put Earth’s primitive conditions to test for the first time in a famous laboratory experiment. It yielded variety of amino acids and organic compounds. The researchers realized something more: that no early form of life could have ever survived the world of today, because of the presence of oxygen that directly attacks at the bonds that holds together complex molecules.
Scientists also now know that the original blueprint of life was not DNA, but short RNA strands that may have also served as their own biological catalysts, before enzymes ever evolved, providing for self-replication. This early RNA world would eventually give rise to DNA, which used RNA as its template for encoding the genetic information to build proteins.
Still, there are several other questions that remain surrounding life’s origins such as How can life be defined? Where did it happen? What came first: replication or metabolism? Could life have happened elsewhere in the universe? What would an alternative form of life and biochemistry look like?
Last weekend, to discuss the questions, a small panel of six scientists gathered at workshop at Arizona State University with a major goal of charting out the steps between the RNA world and greater complexity. Some would say theirs was a hopeless cause and a waste of time.
Then, on Saturday, February 12, a public debate took place between them with an overarching theme entitled, “What is Life?” Theoretical physicist and cosmologist Lawrence Krauss, ASU professor and director of ASU’s Origins Project defended the exercise as uniquely human.
“It’s a profound and deep question that hits at everything we think about,” Krauss said, noting how the question has a powerful draw. “It sounds like a simple question, the answer isn’t so simple. In fact, every time I think about that question, I think about pornography.”
He referred to a 1964 Supreme Court case where Justice Potter Stewart once was asked to explain the definition obscene pornography. “I know it when I see it,” the judge responded. Krauss said, “In some sense, life is like that.”
Life: Complexity with a Specified Direction
Evolutionary biologist Richard Dawkins further elucidated the significance of the question in characteristic eloquence, “This may be the only planet in the universe that contains eyes to see it, brains to think about it, and wonder about it. I don’t believe that. I suspect there is plenty of life in the universe, but this is the only kind of life we know about.”
According to Dawkins, because the laws of physics apply all over the universe, it is likely that life could have materialized many times by the process of evolution by natural selection. Life, then, would have to be defined as anything that is highly statistically improbable, but that appears to have a specified direction.
“You have to add that ‘specified direction’ because with hindsight you could say any old heap of rubbish is statistically improbable in that there has never been a heap of rubbish exactly the same,” Dawkins said. “What’s special about life is that living things are statistically improbable in a direction, which you could have specified in advance. It’s not always exactly the same, but birds are good at flying, fish are good at swimming, moles are good at digging. All living thins are good at something, whereas lumps of rock aren’t.
Whatever life is, it is characterized by its complex molecules that must somehow create the energy to convert raw material into a structure, all while excluding anything that may be toxic to those reactions of metabolism and reproduction. This is why geneticist and Nobel Laureate Lee Hartwell argued, “Inevitably, life will be cellular. Cells will have been selected to have an optimum size and optimum structure for whatever lifestyle they happen to have.”
Searching for a Second Genesis
A sort of definition of what to look for was heartening for NASA planetary scientist Chris McKay, “What Lee said was a beautiful synthesis of how we can search for life, and I want to take that to the specifics of how do we do it in near tem missions in our solar system.”
There is an advantage to finding other forms of life in our own solar system, argued McKay, because “then we’d know that life is common in the universe.” The task of finding other forms of life in the solar system, even on our own planet, is one promoted by cosmologist and astrobiologist Paul Davies
Davies doesn’t see things quite the same way as McKay. “How can we find this second sample of life? Chris has said one way you can do that is you can go somewhere else in the solar system and find it there. That’s great. But it’s also very expensive. Is there another way? Well, no planet is more Earth-like than Earth itself. Shouldn’t it have occurred many times right here on our home planet? How do we know it didn’t?”
While Davies looks for alternative life on Earth—a process that he boldly claims can be completed in less than a decade—biologist and entrepreneur Craig Venter is more interested in creating synthetic life.
Venter explained how he and his colleagues synthesized DNA and chromosomes and inject it into E. coli, which he likened to creating a computer program that builds its own computer, or as he puts it, “A situation where the software actually leads to building its own hardware, but we’re trying to go much further. We had to learn how to boot up this bacterial genome.”
Change the DNA, change the software, and you change the species, Venter explained, and as others have pointed out, his team did use a living cell, but the cell was the first one to ever have synthetic DNA.
Living Artificial Intelligence
Among these scientists, one thing was certain: the definition of life could not be agreed upon in the face of alternative forms of life in the universe, in our own solar system, on the Earth, or from creating life from scratch. But, perhaps, a definition of life isn’t needed after all because, as Krauss put it, anyway, it could change.
“Let me throw it in a completely different direction,” Krauss offered in the debate.”When computers become conscious, which they will—my Mac is far closer than the PC—will we call them life? And they’ll object if we don’t, I suspect. I think the definition is a moving target.”
After all, the difference from what Venter is accomplishing—with software that makes its own hardware—and computers is that computers simply haven’t done that yet (made their own hardware), but when they do, which will happen in at least one or two decades, Krauss said, “they will become the dominant forms of intelligent life on the planet and biology will have to incorporate that in order to keep up.”
At the end of the debate, the inevitability of life in the universe was the lesson really learned, given that there could be life lurking almost anywhere.<
Be it in a biological world, a synthetic world, or another kind, life can defined as simply… we'll just know it when we see it.