Boundaries of free will

I am emphatically non-committal on the question of free will vs. determinism. I think there’s a lot of things in the world that we’ll go to our deathbeds without having clear answers on , and this is one of them. I’m OK letting the unknown be unknown.

But that’s just me. Some of the folks here have definite opinions on the matter, and that’s cool. I understand the determinist argument, even if I don’t fully buy it. I sort of understand the free will argument. We make choices. We are free to choose, A, B, C, or none of the above. No argument here. I would like to understand the free will argument better. To those who believe in free will, I am curious about where you think the boundaries of free will are. 

For example, is there a bright line between humans and other species? Are we the only ones who have free will? If so, is that because God gave it to us and not to animals? Or for some other reason? 

Or do our close cousins like gorillas and chimpanzees also have free will? If they do have it, do they have less of it than we do? And if they have free will, what about dogs? Mice? Ants? Bacteria?

Coming back to humans, is free will an absolute thing, or do our biology and history impinge on it somehow? Under what constraints does it operate?

Inquiring minds want to know! Thank you in advance for your thoughtful replies!