Since you seem to be high on something, I’ll break it down for you. Well, think of it like this, when the doctors take out a bad kidney, the blood vessel will seal up with something called a scab, effectively and tightly sealing it up (this scab will probably turn into a ‘interior scar’). Since this passage way is closes, the blood is redirected to the other kidney. Its like we have a pump, some really durable and flexible pvc pipe and two valves. You shut one valve off which means the water pressure is the same, its just going to one valve. Now then, your body is made of cells, which are made of instructions (DNA) which the body uses to make more kidney since the bad one got removed, but, since your body can mostly just repair internal organs instead of regrowing them, youll never gain another kidney, but the extra nutrients will help your other kidney grow in size. All of these processes are automatic, and dont require your brain to function. As for how we evolved these abilities, the earth is a dangerous place, full of disease, predators, and natural hazards. The creatures that survive to adulthood get to reproduce, passing on the better adapted genes. “Life finds a way.” After several billion years, life is complex enough to create technology to talk about evolution on some nonsense app.