Life in the lab

Another way to determine what alternative life might look like is to try to invent it ourselves.

If we can create new molecules which can behave in life-like way, we may then go out and look for these in the environment, says Professor Steven Benner, of the University of Florida.

His team have created perhaps the closest yet to a man-made alternative form of life.

"We are announcing the first example of an artificial synthetic chemical system capable of Darwinian evolution," he told the conference.

"Is it alive? Well, I can tell you that it is not self-sustaining.

"You have to have a graduate student stand there and feed it from time to time, but it is evolving."

The molecule is essentially a modified version of our own DNA double helix - but with six "letters" in its genetic alphabet, instead of four.

These nucleotides pair up in strands, which can replicate, though only with the help of polymerase enzymes and heat.

"Sometimes mistakes are made in pairing and these mistakes are maintained in the next generation - it is evolving," said Prof Brenner.

"The next step is to apply natural selection to it, to see if it can evolve under selective pressure.

"The accepted definition of life is a molecule capable of Darwinian evolution, so we are trying to put together molecules that are capable of doing it."

But he questioned whether our definition of "living" is perhaps too "Earth-centric".

"Remember - just because you are a chemical system which is self-sustaining and capable of Darwinian evolution, that doesn't mean that is the universal definition of life," he said.

...fine...but what other definitions might we apply. According to my latest reading, life is defined not just as being capable of Darwinian evolution (i.e. hereditary descent with modifications), but is required to consume energy and...something else which I've forgotten right now (D'oh - will look it up and update this).

What caught my eye was the ability to create something life-like with a different DNA coding. Would be interesting to see if you could go the other way and reduce it to two letters - essentially a binary code!