Selection Power and Selection Labor - Human Information Retrieval - page 30

double. The search could be conducted either deterministically or nonde-
terministically with human intervention at intervals, both with unaltered
criteria during the process. The labor invested in description corresponds
to a capital cost that is not incurred for each iteration of searching.
These slightly abstract considerations are helpful in establishing the-
oretical constraints for the labor associated with selection and also for
enforcing the point that labor can be distributed between description and
searching but cannot be eliminated. They also have some more practical
resonances. The purposes of description may require semantic primitives
that are difficult to isolate and may not exist, particularly for human or
social discourse. An approach to theoretical limits can be made in other
aspects of information theory, such as reducing redundancy in messages,
but they are difficult to obtain fully (Shannon 1948/1993, 39; Verdú
and McLaughlin 2000). Biological classifications might offer the closest
analogies to reduction to atomic facts or to a perfectly organized source,
but distinguishing species from variety can be problematic (Darwin
1859/1968, 104-108). Despite these reservations about the possibility
of approaching theoretical limits on the effectiveness of descriptions, the
Box 2.2
Darwin on the Difficulty of Establishing Classifications
Many years ago, when comparing, and seeing others compare, the birds
from the separate islands of the Galapagos Archipelago, both one with
another, and with those from the American mainland, I was much struck
by how entirely vague and arbitrary is the distinction between species and
varieties. On the islets of the little Madeira group there are many insects
which are characterized as varieties in Mr. Wollaston's admirable work, but
which it cannot be doubted would be ranked as distinct species by many
entomologists. Even Ireland has a few animals, now generally recorded as
varieties, but which have been ranked as species by some zoologists. . . .
From these remarks it will be seen that I look at the term species, as one
arbitrarily given for the sake of convenience to a set of individuals closely
resembling each other, and that it does not essentially differ from the term
variety, which is given to less distinct and more fluctuating forms. The
term variety, again, in comparison with mere individual differences, is also
applied arbitrarily, and for mere convenience sake.
—Charles Darwin. The Origin of Species by Means of Natural Selection or The
Preservation of Favoured Races in the Struggle for Life . 1859. (1859/1968, 104-108).