Quiz: Dynamic Programming

What is the obvious reason for the lack of speed of the recurring algorithm of Fibonacci sequence generation (given below)?

$\underline{RecFibo(n):} \\ \hspace{0.4cm} if\space n = 0 \\ \hspace{1cm} return\space 0 \\ \hspace{0.4cm} else\space if\space n = 1 \\ \hspace{1cm} return\space 1 \\ \hspace{0.4cm} else \\ \hspace{0.4cm} return\space RecFibo(n − 1) + RecFibo(n − 2)$