Evidence that dendrites actively process information in the brain

Biology, it seems, is deeply unabstractable. Ie, as one moves up the levels of organization, one rarely (never?) reaches a point where a higher level can be fully modeled without also fully modeling each of the lower levels.

This is in sharp contrast to computer engineering, where, for example, one can model a processor with all practical accuracy by treating the individual as idealized boolean logic (As we move towards smaller and smaller transistors, this abstraction is threatening to become "leaky", but this has been true thus far throughout the Moore-ian advancement).

I suspect that there may be a limit to the degree of complexity humans can "manage", and thus, without the benefit of effective abstraction, there is a limit on the degree of advancement we can achieve in bending biology to our will.

(An example that speaks to this, in my mind, is the fact that our attempts to chemically tweak our own biochemistry (viz. drugs) are hilariously crude (flood the system with a handful of chemicals, which hopefully drives the system as a whole in the general direction we want) compared to the regulation that the body carries out on its own.)

I mean, if I needed (A xor B) and (C or D), then my impression is a single neuron with rather simple geometry and appropriate dendritic connections could calculate that in the sense that this neuron would spike iff the A,B,C,D neurons spiked as required by that formula; but since neurons tend to have much much more connections, then each neuron is technically capable of much more complex calculations, even if many of them in the end do something like 'spike iff any 100+ of my 1000 inputs are spiking'.

It's not so simple as that because timing is also relevant, and there were examples of known dendritic structures that do "processing" in terms that a neuron spikes if it receives A slightly before B, but doesn't spike if it receives A slightly after B; so it can be used for detecting motion direction and such.

For one, you can use directed evolution to optimize a biological system without relying on rational design.

For another, biological development is massively flexible. Consider that when you evolve a longer arm, you don't need to mutate genes to ensure you have longer muscles, tendons, nerves, etc. In fact, you can grow an entirely new arm by just initiating a limb bud at the correct time in development. By contrast, in electrical engineering all design aspects are "rational" - when you change one part, you must change the other parts to compensate.

Modularity and reductionism are "problems" only in the sense that they reflect differences between our engineering strategy and the substrate we are trying to engineer. We must discover the engineering principles that match the substrate.