For the physiological needs in Maslow's hierarchy (breathing, wood, water, sex, sleep, homoeostatis, excretion - to list those in the model shown on Wikipedia), the chemical and biological mechanisms are understood: we know how we breathe, and we know why chemically we need to breathe; we know how oxygen and carbon dioxide are carried around the body.
But for Maslow's other layers, what are the physiological mechanisms? It's likely that dopamine and serotonin will feature in there somewhere. But are all the other layers actually distinct from each other physiologically? If connection with family triggers the same dopamine pathway that problem-solving does, then the fundamental need is not either of those things but the pathway underneath.
Once we understand the physiological basis, we can refine the groupings and disaggregate the cultural/nurture expressions of needs from the true fundamental needs. And we will gain profound insight into the way humans work.
[N.B. although homeostasis is separated out in the model on the Wikipedia page, it actually emcompasses many if not all of the physiological needs]