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“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

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4. The Microbial Self..........................................................

Chapter 4

If amoebas were as large as whales, would you get out of their way?

— H.S. Jennings

Overview: Unicellular organisms express a sense of self, as manifested by their
strong tendency to survive and procreate. Examples can be seen in prokaryotes
and simple eukaryotes (cells with a nucleus) in their feeding behavior, avoidance
of danger and defense of invasion. Some of their behaviors are quite complex.
The unusual ability of slime mold to change from a unicellular to a multicellular
existence and vice versa is a prototype of a flexible self.

Microbes are unicellular organisms that range from the barely visible
to those invisible to the naked eye. They can replicate endlessly and
rapidly, doubling in less than an hour. They have a simple genome
that can mutate rapidly to adapt to a changing environment. They can
extract energy from varied sources for survival. All these properties
make them evolutionarily the most successful (in terms of number)
life forms on Earth. Together they comprise the largest biomass on the
globe — about 80%. These unseen organisms inhabit every millimeter
of land and sea,  and are also found, though in lesser number, in the
air. They live on the highest peak of Mount Everest, thirty thousand
feet above sea level. They survive under high temperatures in thermal
geysers and under enormous hydrostatic pressure on the deepest ocean
floor. Further below the sea floor, they go as deep as 2.5 kilometers.
Within our body, bacteria cohabit with human cells, mainly in the gut,
outnumbering our own by a factor of ten. This chapter is dedicated