@wushiwen
What is the main reason for seasonal changes on earth?
Lets play at universe engineer.
This game lets you design whole system of planets to create life. Lets look in at the game when life is abundant and advancing into complex cell structures.
An issue occurs where you need to harden your life forms to push them into advancement. You can change things about the planet but not directly about them. So you devise a seasoning of the life on the planet. Sometimes they have abundant resources and other lean. This is created by tilting the planet and altering its orbit slightly.