Animals do have guns. Humans are animals. Humans have guns. Evolution made us, we made guns, therefore guns indirectly exist because of evolution.
Or do you mean “why don’t animals have something like guns but permanently attached to them instead of regular guns?” There, I’d start with wondering why humans prefer to have our guns separate from our bodies, compared to affixing them permanently or semi-permanently to ourselves. All the drawbacks of choosing a permanently attached gun would also disadvantage a hypothetical creature that got the accessory through a longer, slower selection process.
Animals do have guns. Humans are animals. Humans have guns. Evolution made us, we made guns, therefore guns indirectly exist because of evolution.
Or do you mean “why don’t animals have something like guns but permanently attached to them instead of regular guns?” There, I’d start with wondering why humans prefer to have our guns separate from our bodies, compared to affixing them permanently or semi-permanently to ourselves. All the drawbacks of choosing a permanently attached gun would also disadvantage a hypothetical creature that got the accessory through a longer, slower selection process.