- Parts of organisms. Studying organs, tissues, cells,
and other constituents of organisms, we find again that their
structure, even down to minute details, must be understood in
terms of the function which the part serves in the life of the
whole organism. The structure of the heart is fine-tuned to
circulate blood (
); the lungs are structured so as
to convey oxygen efficiently to the bloodstream and to expel
the products of oxidation. Of course, these and other organs
may have defects or accidental features. The most important
features, however, are functionally determined, and even the
defects must be analyzed in terms of their adverse effects on
function. There is evidence that even supposedly useless
parts, such as the appendix or tonsils, may have significant
function; moreover, even if a truly useless organ were found,
its existence could presumably be traced to a vestigial
function. The "form follows function" principle is so
all-embracing in life that we should always suspect a life
function, even when one is not immediately apparent.
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