Body Parts

Have you ever wondered why we have two eyes, two ears, two kidneys, two arms and legs, but only one heart? Only one brain? The first mentioned organs are pretty much vital, especially since we were designed by nature to survive  in the wild, so we were given spare parts. But you can't get very far without your brain, even though most of us don't use it as much as we should. You surely can't do much if your heart goes on the blink. That pretty much stops the game. We have only one liver, which cleans our blood, even if we abuse it with alcohol. It's called the LIVER for good reason. If you lose it, you stop LIVING.
 Mickey Mantle was bumped up on the waiting list for a liver transplant, just because he was a great baseball player, amid a lot of controversy. He was legendary for his alcohol consumption, and  famously said, "If I knew I was going to live this long, I would have taken better care of myself." He died anyway.
 Heart transplants are common today, like getting your oil changed. Organ transplants are prohibitively expensive, and nobody could pay for the procedure on their own, except for wealthy republicans. But that's another story.
 My question of the day is why Mother Nature gave us two of some and only one of some others. In the natural world, things make sense in a brutal sort of way. Wolves cull the deer herd of the weak stragglers, thus leaving the healthy and swift to continue to breed and prosper. It's sensible. But giving us a single heart and a single brain makes no sense at all.
 Sometimes we act like we have no heart, and sometimes like we have no brain, but we can't act at all unless we have them.
 My grandfather had one eye. His brother gouged out the other one during a disagreement. My uncle John had a good part of his ear missing. It looked like it was removed by a cookie cutter, but was actually bitten off by a guy with very even teeth who had been ripped off by my uncle, a notorious thief. John was a great fighter, but not good at leaving things alone, or keeping his ears.
 The point is, if Grampa and John had lost their hearts or brains, they would have died instantly. They were lucky enough to have spare parts. Having any vital organ as a single option only is a serious design flaw. Unfortunately, there is no known way to complain to the manufacturer.