Verified answer

All life forms that we know of require water, and a typical cell is about 70% water. So, the presence of water—especially liquid water—on Mars raises the possibility that lifeforms similar to what we find on Earth could also exist there. Solid water (ice) means it is possible that such lifeforms existed there in the past, at some point when the conditions on Mars were different and what is currently ice may have been large bodies of liquid water. Does that make it more likely that live evolved there? Well, it certainly makes it a possibility, but without any firm evidence that life evolved on Mars, all we can do is make educated guesses. So I guess I would say yes, water on Mars makes its more likely that life arose there, but it is still a remote possibility in the absence of more firm evidence, like fossilized remnants of ancient cells or other chemical and physical signatures that are characteristic of living organisms.

As for other physical factors that might be important, there are a lot of possibilities. In addition to water, one of the major requirements that all known living organisms have is the availability of carbon and a few other elements to make proteins and other molecules. Carbon is arguably the most important, but we also need hydrogen, nitrogen, oxygen, sulfur and several others. Life on Earth can survive in many different conditions. Another requirement is some sort of energy source, either radiation or chemical energy. As far as I know, carbon and other elements, and energy sources do exist on Mars, so it is at least possible that life did originate there and then come to Earth on a comet or by some other means. However, there is no hard evidence that life arose on Mars, and there is no good reason to think that it could not have evolved right here on Earth. In fact, since Earth is the only place where we know for a fact that life did evolve, the most reasonable conclusion, without any other evidence to go on, is that life arose here.

That argument has always seemed odd to me. Behe talks about the complicated Rube Goldberg interactions of molecules in the cell as if such unnecessarily complicated mechanisms were more easily explained by an intelligent designer. They aren't. They are in fact the reason that simple, random changes to the DNA code can improve the ability of the organism to survive and reproduce in its environment. Consider computer code, written by an intelligent designer to accomplish some specific task. Change a letter here or there in the code and you're most likely to end up making the program unexecutable. A few changes might still allow some functionality, but it's hard to imagine a random change that would improve the functionality of the program. That's because the code was written by an intelligent designer, and if that designer wants to improve the functionality of the program she can do it herself. Each letter and word of code has meaning, and is important to the proper functioning of the program as designed. The DNA -> RNA -> Protein -> functionality system of cells doesn't work like that. DNA doesn't code directly for any particular functional result. Rather, DNA establishes the blocks used to build proteins, and different blocks may or may not change the shape of the proteins - either slightly or significantly. It is the shape of the proteins that lets them serve their functions in the cell - for instance by binding simultaneously with two other molecules so those molecules can bind with each other. So picture an early, relatively simple cell. It already has a network of interacting proteins floating around, interacting with each other and with other molecules in Rube Goldberg ways, doing things necessary for the cell's continued functioning. Now picture a piece of mRNA, recently transcribed from a gene, getting reverse-transcribed back into a new position in the DNA. This is called gene duplication, and results in two copies of the same gene. Both are putting out the same protein. The protein from the second copy may not do anything useful, but it happens anyway. Now suppose there's a small copying error in the second gene causing it to put out a protein with a slightly different shape. The protein from the first gene is still performing its function, so the second gene is free to mutate. The newly modified protein goes out into the cell and interacts with the existing Rube Goldberg systems of molecules. Possibly it does something useful, possibly not. If it does something detrimental, then the individual will be less likely to survive and reproduce, and the mutation will get weeded out of the population over time. If the mutation instead does do something useful, then the individual with the mutation will be more likely to survive and reproduce, and the proportion of individuals in the population with the mutation will increase from generation to generation until eventually everyone has the mutation. This will likely mean an increase in the complexity of one of the Rube Goldberg interactions, or else the addition of a new simple interaction. Thus, if no intelligent designer were present, we'd expect to see populations in which the complexity of interacting Rube Goldberg systems goes up over time. We would not expect to see the sparse, to-the-point lines of intelligently designed code in a computer program. We do in fact see the former and not the latter.