I know you can get a transplant and there are machines, but I'm just thinking how weird it is that evolution (or a divine creator if you prefer) set humans up to have two kidneys and so on, but there's only one heart even though the heart is basically the most critical and important organ other than the brain. So the less important organs you get a back up, but the most important one of all you only have one. I just think its weird how that is.
I've read in the Star Trek universe the Klingons have at least two hearts and stuff, and that was because of how they are warriors and always suffering injuries and stuff which makes them more resilient. Star Trek is of course fiction, but this makes sense. Why aren't humans like that? If Darwinism is about the survival of the fittest then having a backup heart is obviously something that would increase the fitness of an organism, so why hasn't this happened? Yet we have two kidneys and two lungs and so forth? Why?