Dawkins saw the question as a biological equivalent of one posed by Einstein: Did God have any choice in making the universe? Not that Einstein believed in a biblical God, as the famously atheistic Dawkins was quick to point out.
Dawkins noted that 99 percent of the living things that ever existed are now extinct. The way carbon-based life works on Earth is downright wasteful, he said. "Any decent engineer would have sent it back to the shop."
The event, which drew more than 3,000 people, was held at Arizona State University in Tempe. Dawkins didn't lecture but instead took part in an onstage discussion with Krauss, who runs a multidisciplinary program there on the origins of humanity, life, and the cosmos.
Krauss - while not going so far as to say alien chicks would be hot - did say the laws of physics and chemistry might favor carbon-based life resembling ours.
Dawkins said he was inclined to think life could exist in more diverse forms, as long as it included some kind of code-carrying system equivalent to DNA, copying itself with high fidelity. Such genetic material is critical for Darwinian evolution, which, to Dawkins and many others, is the defining characteristic of life.
Perhaps it wasn't a complete coincidence that at the same university, biochemist John Chaput was creating an alternative version of DNA, called TNA, and had last month published the first evidence that the stuff can undergo Darwinian evolution.
Chaput, who works at ASU's Biodesign Institute, said Dawkins is correct to emphasize the need for genetic material - something that can carry a code. All known life does this with DNA and RNA.
