We all have two of certain organs, like kidneys and lungs, but why not multiple hearts, livers or brains?
“Humans have body plans that are bilaterally symmetrical. This means that if you draw a line down the centre of the human body, from the middle of the head to the feet, the same features appear on either side.”
Why do you have two lungs but only one heart?
“Your vital organs — like your lungs, your heart, your pancreas, brain and liver — are just that, vital. Not only are they vital to life, they are also vital to one another.”
Why have one heart but two kidneys?
“It’s not just us that are bilaterally symmetrical. All vertebrates are – be they birds, reptiles, frogs, or fish. In fact, not just vertebrates but almost all other animals are bilaterally symmetrical as well.”
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