Humans have a unique creative, intelligent and relational nature.
These together are a clear distinction.
Hard to detect that from your skull alone.
Perhaps we can think of something a bit more concrete.
Why don't IDers ask themselves this: wouldn't the "intelligence" involved in the "design" of life have to evolved somehow, and if not, what designed the designer. Was Yahweh designed by Zeus, who in turn, was designed by Odin? Why can't they ever tell us who this designer is, or what its nature is, without resorting to the Bible or the Koran, or any number of other pre-scientific texts?