As far as I know, it’s all down to the evolution of our brains. Because we’ve developed much greater intelligence than most other creatures on Earth, we don’t need to rely so much on our other senses to protect ourselves from danger. Our intelligence combined with very skillful hands means that we can use tools and weapons to enhance our natural strength and senses. This would mean that there is less evolutionary pressure to keep things like a good sense of smell or hearing, although our eyesight is still better in many ways than a lot of predators!
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