Simplify the following text for a Grade 15 native English-speaking person.
Original: Simple modelling , invoking small mutations exposed to natural selection , demonstrates that a primitive optical sense organ based upon efficient photopigments could evolve into a complex human-like eye in approximately 400,000 years .
Simplified: Simple modelling , supposing small mutations exposed to natural selection , shows that a primitive optical sense organ based upon efficient photopigments could evolve into a complex human-like eye in about 400,000 years .