We will probably both agree that we are the result of millions (actually billions) of years of evolution. If you argue that humans have free will, you inevitably have to agree that other mammals have it too.
Our human ancestors split off the last hominid group around 400,000 years ago? So other mammals like modern monkeys which developed parallel to us must have free will too. If you claim they don't, isn't that pretty arbitrary and arrogant for humans to claim?
Also: Do tigers, polar bears and dogs have free will too?
And most importantly, WHEN did this event happen that living organism suddenly were composed of this entity called "free will"? Was it 400,000 years ago with a sudden mutation or inter-species mixing and all of a sudden it was there? Or did free will always exist and even microbes from which we originally descend have it? You would have to admit that microbes having free will sounds a bit outrageous.
Whimminz reactions when I try to be more "confident":