A simple theory is that, since the Big Bang, humanity has been predetermined to exist.
Let's presume no intervention by a supernatural being and also, let's presume consistent physical laws from a macro (newtonian) through a micro (quantum) level.
For systems with a small number of particle interactions, for example our solar system, we can predict with great accuracy, eclipses, phases of the moon, and sunrise & sunset. To predict these, we only need to concern ourselves with three objects (Earth, sun, and the moon).
But, for us to calculate systems with many more particles, such as the weather on Earth, it becomes more difficult. Although the roll of a die may seem random, it's not - we just can't calculate all the variables involved.
Let's suppose, for argument sake, that there is no other life in the universe. That would mean, since the Big Bang, 15 billion years ago, that intelligent, sentient and sapient life was destined to arise on Earth.
Considering that a universe (or any system) devoid of life would be devoid of free will, then the first life evolving anywhere in our universe was destined to happen.
Which raises an interesting point about free will. If an entire human's existence is destined by the laws and interactions of physics how do we generate true randomness which we call free will?