The phrase "biological underpinnings" means the fundamental or basic biological factors or processes that are responsible for something. Full definition
«Brain anatomy differs in people with 22q genetic risk for schizophrenia, autism: Deletions or duplications of DNA along 22nd chromosome hint at biological underpinnings of these disorders.» (sciencedaily.com)
But here's the interesting variable that provides evidence for possible biological underpinnings: 53 of the studied competitors were blind. (scientificamerican.com)
So if researchers think that an individual drug for, say, chronic myeloid leukemia might work against a different kind of tumor because the two illnesses share similar biological underpinnings, they have to conduct a whole new clinical trial and go through the approval process all over again for the second condition. (scientificamerican.com)