Determinism, Ends, Means

Many would agree that the behavior of a human organism is predetermined by some biological principle, e. g. to survive.  However, such a principle leaves indeterminate the means sought to achieve that end, thereby not precluding the possibility of Free Will as also a factor in the organism's behavior.  Accordingly, to fill the gap, Determinists often argue that if all the facts of its experience over the course were known, every new episode would be revealed as the effect of one or more prior influences.  Now, one straightforward response is that all the facts are not known, so that hypothesis does not prima facie suffice to rule out the possibility of either Free Will or Chance contributing to that experience.  Furthermore, the assertion begs the question--even granted the antecedent, there is no reason to deny that those facts are indeed sufficient to ground all that transpires thereafter. So, despite the dogmatic reductionism, there seems to be no good reason to reject the empirically sound thesis that human behavior combines determinacy and indeterminacy, perhaps distinguished as Ends and Means.