can assume that any living creature must be built from atoms with
the capability of forming highly organized systems. Despite previous
comments about the subordination of material to arrangement, some
materials are simply inappropriate. We cannot build a digital computer
from wood, or even from metal using the crude shaped-metal technology
of a century ago. Charles Babbage, mentioned in Chapter 5, understood
and outlined the principles of a punched-card-controlled digital
computer with a stored and modifiable program in 1833, but the technology
of his time was inadequate to construct one.
Similarly, we cannot conceive of a living organism as being built
mainly from ionic compounds. Nondirectional forces between ions
do not permit the necessary degree of complexity. The main reason
why we can claim "no life but carbon life" is that we see no
other element in the periodic table that is capable of the extensive
and varied molecular chemistry shown by carbon. There are good reasons
why life is found only in a restricted range of size and temperature:
This is the size range of macromolecules based on carbon, and of
larger assemblies of such macromolecules; and this is the temperature
range within which these compounds are relatively stable, yet reactions
between compounds are reasonably fast.
can summarize the arguments of this chapter by stating that life
is the most exciting and challenging property exhibited by matter.
It is a behavior pattern shown only by complex and well organized