Why does Nautilus have that spiral?

The splash in the above picture is Fibonacci spiral, a rectangle with Fibonacci numbers as sides, and then draw a 90-degree fan in the square, and the connected arcs are Fibonacci spiral. Nautilus also contains Fibonacci spiral. For Fibonacci number, you can also refer to the article of the Scientific Squirrel Society, a squirrel problem in 800. Fibonacci series, also known as golden section series. Mathematically, Fibonacci sequence is defined recursively: F0 = 0f1=1fn = fn-1+fn-2. Literally, Fibonacci series begins with 0 and 1, and the Fibonacci series that follows is the sum of the first two numbers. The first Fibonacci series is: 0, 1, 1, 2, 3, 5, 8, 13, 2 1, 34, 55, 89, 144, 233, 33.