  The emergence of the main divisions of today's life: (1) unicellular
prokaryotes, (2) unicellular eukaryotes, (3) multicellular eukaryotes, and (4)
metazoans, are examples of the--still unexplained--major transitions in
evolution. Regarding the origin of life, I have proposed that primordial life
functioned as heat engine (thermosynthesis) while thermally cycled in
convecting volcanic hot springs. Here I argue for a role of thermal gradients
above submarine hydrothermal vents (SHV) in several major transitions. The last
decade has witnessed the emergence of phononics, a novel discipline in physics
based on controlled heat transport in thermal gradients. It builds thermal
analogs to electronic devices: the thermal diode, the thermal transistor, the
thermal switch, the thermal amplifier, the thermal memory--the thermal computer
has been proposed. Encouraged by (1) the many similarities between microtubules
(MT) and carbon nanotubes, which have a very high thermal conductivity, and (2)
the recent discovery of a silk protein which also has a very high thermal
conductivity, I combine and extend the mentioned ideas, and propose the general
conjecture that several major transitions of evolution were effected by thermal
processes, with four additional partial conjectures: (1) The first organisms
used heat engines during thermosynthesis in convection cells; (2) The first
eukaryotic cells used MT during thermosynthesis in the thermal gradient above
SHV; (3) The first metazoans used transport of water or in water during
thermosynthesis above SHV under an ice-covered ocean during the Gaskiers
Snowball Earth; and (4) The first mammalian brain used a thermal machinery
based on thermal gradients in or across the cortex. When experimentally proven
these conjectures, which are testable by the methods of synthetic biology,
would significantly enhance our understanding of life.
