  Physical emergence - crystals, rocks, sandpiles, turbulent eddies, planets,
stars - is fundamentally different from biological emergence - amoeba, cells,
mice, humans - even though the latter is based in the former. This paper points
out that an essential difference is that as well as involving physical
causation, causation in biological systems has a logical nature at each level
of the hierarchy of emergence, from the biomolecular level up. The key link
between physics and life enabling this to happen is provided by biomolecules,
such as voltage gated ion channels, which enable branching logic to emerge from
the underlying physics and hence enable logically based cell processes to take
place in general, and in neurons in particular. These molecules can only have
come into being via the contextually dependent processes of natural selection,
which selects them for their biological function. A further major difference is
between life in general and intelligent life. We characterise intelligent
organisms as being engaged in deductive causation, which enables them to
transcend the physical limitations of their bodies through the power of
abstract thought, prediction, and planning. Ultimately this is enabled by the
biomolecules that underlie the propagation of action potentials in neuronal
axons in the brain.
