For much of human history, a central question has been, "Does Free Will exist."  Throughout most the Anno Domini Era, general opinion was that it did not.  This belief was called Determinism as it considered all human action and fate to be pre-determined. 

These beliefs were intertwined with theological belief in that some supernatural sentient force was controlling everything. 

Much has been discovered since then, in terms of science, the stars and the human body.

Dopamine is a hormone that serves as a neurotransmitter in human brains; it can deliver messages across brain cells, particularly messages regarding the human's binary opinion of whatever is happening.  You've probably heard of it as a key functionary in the human reward system.

If a human tastes something they enjoy, the dopamine message will be affirming.  If not, the message will indicate aversion.  Dopamine drives human motivations and ultimately self-identity.

Human beings typically will spend a considerable portion of their lives performing habitual tasks.  We are creatures of habit.

For the first several thousand years of human civilization the percentage was likely even higher than it is today.

In the mid-1300s, a Pandemic of the bubonic plague decimated much of the world, killing millions upon millions of human beings.  It took over a hundred years to somewhat contain it.  

The massive deaths, however, led to higher wages and likely fueled the Renaissance that would soon follow and ultimately the political philosophy that became Classical Liberalism, the framework that underlies all modern Western Democracies. 

Dopamine is a major driver behind human habits.  Some activities may hijack the human reward system, providing dopamine for something that ideally would be avoided, such as excessive use of inebriants or listening to angry, ornery orators.

Humans seem to have the capacity to change their habits though, and in so doing, build a new identity.  They can lose weight, stop gambling, curb inebriant consumption, even alter their entertainment habits and reveal a new identity.

My maternal grandmother stopped listening to several suspect radio talk shows and her disposition changed considerably; in later life, her anger was replaced with joy.

As such, it seems to my primitive programming that free will does indeed exist and all humans possess the power to prove it.