Humans have two kidneys mainly due to evolutionary reasons, providing functional reserve and backup in case one kidney is injured or diseased. Early humans with two kidneys had a better chance of survival and reproduction, thus passing this trait down genetically. Kidneys also follow the body’s bilateral symmetry pattern, where paired organs exist on both sides of the body. While it is possible to live with just one kidney, having two offers extra capacity to filter blood, maintain bone health, regulate blood pressure, and produce blood cells. The two kidneys also ensure that the body's waste removal and other essential functions can continue even if one kidney gets damaged or stops working. Having two kidneys represents a balance between adequate organ function and the constraints of organ size and placement during development. In summary, the presence of two kidneys provides redundancy for survival, follows the bilateral symmetry of the body, and enhances physiological resilience in case of injury or disease.
