The Evolutionary Theory (very often said as 'Evolutionary THEORY') is a THEORY of human evolution. There is often emphasis on the THEORY part, due to it being widely believed that humans will die at before there will be any sort of 'Evolution'.
This is often used in chats as something said after someone had said something incredibly stupid.
Another way this is said, is when somebody is speaking very seriously about the distant future.
1. P1: 'Hey man, why did the chicken cross the road?
P1: 'To get to the other side!'
P2: 'The Evolutionary Theory'
2. P1: 'Do you know the sun is going to blow up in 2 billion years?'
P2: 'The Evolutionary THEORY'