Reductionism has been a powerful tool for a long time now, and it’s not going away any time soon. There, that should be enough of a 50,000-foot opening! The idea that you can understand a system by taking it apart and looking at the pieces doesn’t always work out, but it still seems to be the best way to go about it. And even if said system turns out to be more than just the sum of its parts, knowing what those parts are and what their immediate functions are is not a step that can be skipped, either.
Consider (philosophy again!) that all we know about the physical world is from what we can take in from our senses. How, exactly, do we do that? We’ve known for a long time now the main details of how light signals get sent to the brain: the eyes have a light-sensitive layer, the retina. When looked at more closely, the retina turned out to have particular cells, rods and cones, that were responsible for black-and-white and color vision (as an amateur astronomer, I’m used to extended sessions where my cone cells do hardly any work at all, since most deep-sky objects are too dim to set off any color vision response). When looked at more closely in turn, these cells turned out to contain particular pigments that were somehow light-sensitive, and when those were looked at still more closely, everything was found to hinge on photochemical isomerization of carbon-carbon double bonds. Reductionism in action – you start by wondering about your eyeballs, and you end up talking about molecular orbitals.
Similarly, sound is transduced by the actions of the small bones of the inner ear, and then by the hair cells therein. But past these two senses, things get a bit less obvious. It’s clear that through our skin we can sense relative temperatures, along with pressure and other kinds of touch but how, exactly, do we do that? Eventually, these things are also going to have to come down to molecular-level mechanisms, just like vision. There are, in fact, ion channels that are sensitive to physical deformations of the cell membrane, several classes of them, and these seem to be largely responsible for the molecular-level sensing of touch, pressure, and so on. (They’re also involved in hearing, when you get down to the level of asking how the movement of the individual hairs in the hair cells gets turned into some sort of cellular signal). These same types of receptor, and the specialized cells bearing them, also show up in things that we don’t sense directly at all, such as the regulation of blood pressure.
Temperature sensing seems to divide out into separate classes of hot- and cold-sensing receptors, but it appears that these may work through a common mechanism. That link is another trip down the reductionist manhole – you start off wondering how you can sense that something is hot or cold, and you end up thinking about entropic/enthalpic balancing in protein conformational states and changes in molar heat capacity, which is what it all comes down to. As you might figure, it turns out that compounds like menthol activate a particular cold-sensing channel, while capsaicin from peppers activates a heat-sensing channel, so the English language’s confusion between “temperature hot” and “spicy hot” is an honest one.
Since I work in the drug industry, reductionism is the reason I still have a job. The idea, drained of all human feeling, is that individual drug substances can make enough of a difference in the health of a person so that said person will be motivated enough to pay money for them. The reductionist pathway is person/organ system/cells/biochemical pathway(s)/individual proteins/small molecule ligands, and it works well enough, at times, to pay the bills and save some lives. Long may it continue to!