We have 2 lungs, too. We can donate 1 of our kidneys or 1 of our lungs.
We have 2 sides of the brain, and 2 eyes, ears, nostrils, but only 1 heart. Our 2 eyes and 2 ears help us see in 3D and hear where a sound is coming from. Our 2 arms and 2 legs help us move and do things.
We and lots of other animals have this symmetry, where there are many things the same on our 2 sides. It's how we evolved. Here's an article in wikipedia about our 'bilateral symmetry' and all the other kinds of symmetry in living things:
symmetry in biology
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