system
Given the following post, respond as if you're commenting on Reddit:
human
Why did we evolve with different blood types?
gpt
Simple answer: because nothing stopped it from happening. 

There is a huge misconception about evolution, wherein everything is done to optimize us. That's not the case at all. Evolution does not optimize life unnecessarily. It weeds out that which is unable to pass along genetics. I'd love to fly, but until something comes along that kills every human without wings, most of us will stay on the ground.