system
Given the following post, respond as if you're commenting on Reddit:
human
Why didn't the human ribcage evolve to to completely surround our torso?

Our backside seems well protected, but our stomach and other organs don't have that protection. What gives?
gpt
Evolution doesn't perfect living beings, it just optimizes them for reproduction. Basically, if a better ribcage doesn't result in more babies, it doesn't get passed on. An unprotected backside results in fewer babies, so those with protected backside pass on those genes.