characteristic must have been segregated from a community. It seems
likely that precellular evolution also involved the segregation of chem-
ical constituents from many sources.

The complexity of living organisms astounds all students of biology,
and the more knowledge the observer has the more astounding do the
facts appear to be. Is it not true that the development of a particular
minute drop of clear protoplasm, such as a fertilized egg, into a sea
urchin and nothing else is one of the greatest wonders of which we
have knowledge? Yet the study of the compounds of carbon, nitrogen,
oxygen, and hydrogen shows us that a very great variety of these com-
pounds is possible. Two illustrations of the varieties of the molecules
can be given. The human egg contains strands of total length of about
1 meter long of deoxyribonucleic acid containing about 10⁹ units, each
of which can be chosen in four different ways. The number of possible
molecules becomes 4¹⁰⁹, which is an immense number. To specify a
human being at each moment of its existence requires less specific
information; much redundancy is possible and surely exists. Again
the number of possible proteins consisting of, say, 170 amino acids of
20 kinds is very great. If one of each kind were placed in a cubical
box, the length of the edge of the box would be 10 raised to nearly the
50th power light-years. Not all the possible protein molecules exist
now in the observed universe nor could they have existed during the
last 4.5 billion years.

Natural phenomena are very complex in all their various manifesta-
tions. We can follow in considerable detail the more simple and iso-
lated examples of these phenomena, for example, many chemical reac-
tions and structures, the structure of atoms and the nuclei of atoms,
and the gross structure of stars and galaxies of stars. The details of
natural phenomena exceed in complexity the complexity of structure
of the human brain, and we cannot follow these except in an approxi-
mate way. But we can say something about the comparative com-
plexities of the chemistry of the carbon, nitrogen, oxygen, hydrogen
compounds and those of other elements. I shall state my conclusion
categorically in this way. There is no known chemistry of other ele-
ments which approaches in ordered complexity that of these four ele-
ments, and we know enough of the chemistry of all the elements that
we can be certain that no other such chemistry exists. Only these ele-
ments supply such a complexity of compounds and chemical reactions
that we are forced to conclude that only the chemistry of these ele-
ments could supply the complexity of structure and behavior which
we recognize as those of living things. A system of life based on other

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