All living cells interact dynamically with a constantly changing world. Eukaryotes in particular, evolved
radically new ways to sense and react to their environment. These advances enabled new and more
complex forms of cellular behavior in eukaryotes, including directional movement, active feeding, mating,
or responses to predation. ...
All living cells interact dynamically with a constantly changing world. Eukaryotes in particular, evolved
radically new ways to sense and react to their environment. These advances enabled new and more
complex forms of cellular behavior in eukaryotes, including directional movement, active feeding, mating,
or responses to predation. But what are the key events and innovations during eukaryogenesis that made all
of this possible? Here we describe the ancestral repertoire of eukaryotic excitability and discuss five major
cellular innovations that enabled its evolutionary origin. The innovations include a vastly expanded
repertoire of ion channels, the emergence of cilia and pseudopodia, endomembranes as intracellular
capacitors, a flexible plasma membrane, and the relocation of chemiosmotic ATP synthesis to
mitochondria that liberated the plasma membrane for more complex electrical signaling involved in
sensing and reacting. We conjecture that together with an increase in cell size, these new forms of
excitability greatly amplified the degrees of freedom associated with cellular responses, allowing
eukaryotes to vastly outperform prokaryotes in terms of both speed and accuracy. This comprehensive new
perspective on the evolution of excitability enriches our view of eukaryogenesis and emphasizes behaviour
and sensing as major contributors to the success of eukaryotes.
