triggered by predator-avoidance and prey-detection systems. These
systems, as I said above, detect agents but do not specify what type
they belong to.
For me, the connection with predation may also illuminate a char-
acteristic of Fang ghosts that I used to find puzzling. The ghosts, as I
said, are the fleeting presence of dead souls that have not yet reached
the status of ancestors. Now people who report actual encounters with
these spirits often mention that they could watch them but not hear
them or conversely that they heard their voices but could not see their
faces. For many people this discrepancy (sound without sight or sight
with no sound) is also what made the encounter particularly weird and [147]
frightening. This is not unique to the Fang. The dissociation between
modalities is a frequent feature of encounters with supernatural
agents. For a long time I had no idea why this should be especially
uncanny and unsettling, but Barrett's ideas about hyperactive agent
detection might suggest an explanation, since predation is one of these
contexts where hearing without seeing (or vice versa) is particularly
dangerous. This, however, remains largely speculative.
To return to firmer ground, Barrett is certainly right that our
agency-detection systems are involved in the construction of religious
concepts. But this explanation needs to be fine-tuned. Consider this:
Like everybody else, you must have had many experiences of hyperac-
tive agent detection—that is, of interpreting some noise or movement
as indicating the presence of an agent. But in many cases it turned out
there was no agent. So the intuition that there was one was quickly
abandoned. This is natural. It makes sense to "overdetect" agents only
if you can quickly discard false positives; otherwise you would spend
all your time recoiling in fear, which is certainly not adaptive. But
thoughts about gods and spirits are not like that. These are stablecon-
cepts, in the sense that people have them stored in memory, reactivate
them periodically and assume that these agents are a permanent fix-
ture in their environment. If Barrett's interpretation makes sense—
and I think it does—we now have to explain how such overdetection,
far from being abandoned when there is little evidence of the agents'
being around, is in fact maintained and becomes stable.
In particular, we need to see how some intuitions about agents in
our surroundings are given a stable form by what people around us say
about them. Kwaio people interpret some inexplicable shades in the
forest as the presence of adalo. Many of my Fang acquaintances
reported having seen an animal suddenly disappear in the forest, leav-
WHYGODS AND SPIRITS?