I don't want to start a derail, but what digital nature?
Erm, I agree that "digital" is a loaded term. I would say "switching" nature but that is a loaded term as well. The behavior of interest, though, is the ability to map a larger set of external states to a smaller set of internal states in a way that offers utility of survival to some system.
Let me explain:
If a system S exhibits a behavior X that tends to increase the chances of S existing in a form that exhibits X at some point in the future, then all else being equal S will have a higher chance of not only existing but furthermore existing in that specific form at some point in the future.
Contrast this with a system that exhibits no such behavior -- all else being equal, such a system has no influence over the chances of its own existence at some point in the future.
The only type of behavior that satisfies this constraint is what I referenced above -- call it "digitization" or "discretization" or "switching" or "computing" or whatever, it doesn't matter. By mapping a large set of external states to a smaller set of internal states, a system effectively "decides" something.
And a "decision" is the only way for a system in a relatively constant configuration to increase chances of survival -- in some external states, the system goes to a certain internal state that increases its chances, in other external states, the system goes to another internal state.
The essential feature of this behavior is that by having a smaller set of internal states than external states the configuration of the system can remain constant enough to be able to exhibit the same type of behavior in the future.
If you actually look at life in detail, you will see that this is the one feature shared by all aspects of it. Nucleotide polymers were able to come out of the primordial gunk precisely because their propagation mechanism is able to map a large set of external states to a smaller internal one, namely "if another molecule near me is potentially part of a similar polymer, I will react with it to form another polymer." Another polymer which continues on into the future. Cells are built of thousands of such chemical reactions, each of them acting in a discrete fashion, allowing the cell to "decide" what to do in numerous external states. Too much salt in the surrounding fluid? Do X. Detect chemical messenger molecules on my surface? Do Y. Internal division clock reached a threshold? Do Z.
Fast forward to an entire organism, that uses neurons to decide things for it. Something cutting my arm? A neuron maps the million possible things that could be happening to a simple set of pulses. Photons hitting my eye? A neuron maps the infinite possible combinations to a simple set of pulses. Pulses which can be used for the purpose of extending my life into the future, so that the neurons which generated those pulses ( and everything else that is part of me ) can continue to exhibit the same behavior in the future.
Thus, "quantal" behavior as you call it is a sort of magic. It leads to systems that keep themselves existing by active behavior, like life.