Perhaps the most well-known use of the term "contingency" in biology
comes from Stephen J Gould who viewed evolution as the product of a
series of contingencies that occurred under a set of initial and
boundary conditions so unlikely to be repeated that if one rewound the
"tape of life" the outcomes of evolution such as human beings would not
happen again. The fractious debate that has erupted over this radical
idea also operates at the cellular and molecular levels where
evolutionary studies offer a deeper view of contingency. A particularly
critical juncture in the tree of life was the appearance of
multi-cellular organisms. The unicellular lifestyle is one in which a
single cell is fully competent to deal with environmental complexity and
its many contingencies. Metazoans are collections of specialized cells
that can only survive in the context of the organism and these cells are
collectively required for the survival of the organism. The cellular to
organismal transition in the hierarchy of biological organization is, in
part, encoded in a novel genomic system of non-coding RNAs that is
associated with cell specialization in multi-cellular organisms and the
unique contingencies encountered by specialized cells.
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