It is estimated that there are more than 10 million perhaps 100
million living species on Earth today. Each species is different, and each
reproduces itself faithfully, yielding progeny that belong to the same species:
the parent organism hands down information specifying, in extraordinary
detail, the characteristics that the offspring shall have. This phenomenon of
heredity
processes, such as the growth of a crystal, or the burning of a candle, or the
formation of waves on water, in which orderly structures are generated but
without the same type of link between the peculiarities of parents and the
peculiarities of offspring. Like the candle flame, the living organism must
consume free energy to create and maintain its organization; but the free
energy drives a hugely complex system of chemical processes that is specified
by the hereditary information.
Most living organisms are single cells; others, such as ourselves, are vast
multicellular cities in which groups of cells perform specialized functions and
are linked by intricate systems of communication. But in all cases, whether we
discuss the solitary bacterium or the aggregate of more than 10
form a human body, the whole organism has been generated by cell divisions
from a single cell. The single cell, therefore, is the vehicle for the hereditary
information that defines the species (Figure 1-1). And specified by this
information, the cell includes the machinery to gather raw materials from the
environment, and to construct out of them a new cell in its own image,
complete with a new copy of the hereditary information. Nothing less than a
cell has this capability.is a central part of the definition of life: it distinguishes life from other13 cells that
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