38 Beth Preston
the survival and reproductive success of its possessors that it has persisted and
proliferated while the variants have slowly but surely disappeared. As Ruth Millikan
puts it:
The [proper] functional trait must be one that is there in contrast to others that are not there, because
of historic difference in the results of these alternative traits. It must be tied to genetic materials
that were selected from among a larger pool of such materials because of their relative
advantagiousness.... Graphically, whether my shoulders have as a biological [proper] function to
hold up my clothes depends not on what proportion of my ancestors used their shoulders that way
to advantage but on whether there were once shoulderless people who died out because they had
nothing to hang their clothes on. (Millikan 1993: 38)
A diffi culty noted immediately concerned change or loss of proper function. For example,
feathers are thought to have been originally selected for thermoregulation, and only more
recently, in the case of the wing feathers of birds, for their aerodynamic capacities. More-
over, wing feathers may have lost their capacity for thermoregulation in the process—they
may now be vestigial with respect to that earlier proper function. To solve this problem,
the account of proper function was adjusted to appeal to recent selection (Godfrey-Smith
1994) or to a recent evolutionarily signifi cant time period (Griffi ths 1993). This adjustment
is known as the modern history account of proper function.
However, Peter Schwartz (1999, 2002) suggests this adjustment itself needs adjustment.
The problem is that for many traits there has been no selection in recent evolutionary
history, even though there was selection in the distant past. Schwartz identifi es two reasons
for this: 1) lack of recent variation, and 2) the possibility that of two currently maintained
performances, the one that is now undergoing selection is not the one originally selected.
The wing feathers of birds might be an example of (1) if there has been no signifi cant
variation in the recent evolutionary past. And they might be an example of (2) as well.
Suppose there is a variation in the wing feathers that renders them simultaneously better
for fl ying and better for thermoregulation. But suppose (what is plausible, given global
warming!) that there is current selection pressure only for airworthiness. Then the variation
might be selected for fl ying effi ciency alone, even though it continues to perform its origi-
nal, thermoregulatory function, and does so better than ever. We may call this problem
ambiguous variation. In both cases—lack of recent variation and ambiguous variation—we
want to say that the proper function is retained, but because it is not currently being
selected for we cannot do so. To solve this problem, Schwartz recommends an account
with two conditions. The proper function of a trait is a performance that was a) selected
for in the distant past, and that has b) continued to contribute to the fi tness of the organism
in the recent past. This continued contribution to fi tness may be in the form of enabling
survival or reproductive success in some way without variation or selection. Schwartz calls
this the continuing usefulness account of proper function. It weakens the previous total
reliance on selection to pick out proper functions by requiring selection only at some point