Why do mammals have four limbs? Imagine this. You're speaking on the phone holding it in your left hand, looking at the watch on your right one, sipping from a cup of coffee in your third hand, and opening your laptop to turn on a new Bright Side video with your fourth hand. How’s that for convenience?

You see, fish began to crawl out onto land about 500 million years ago. It had four fins that started to turn into limbs during evolution. This way, amphibians could move through the mud. The further these amphibians went, the more their fins looked like legs. But what if evolution had changed its course a little?

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