No Life on Mars

There never was life on Mars. If there had been life, there still would be. Life evolves faster than planets freeze (or lose their atmospheres to solar wind when their magnetic fields wink out). Life is too fast, too clever, too versatile, and too varied to give up a planet, even a forbidding one like Mars.

Maybe the life on Mars was different from life on Earth in that it didn't evolve well. It was too evolutionarily feeble to keep ahead of geologic changes. That seems unlikely, however. If Martian life didn't evolve well, where did it come from in the first place?