254 Tim Lewens
possibility that small populations can thereby “drift” toward the bottoms of small adaptive
peaks, which allows them to scale even higher peaks through the action of selection.
Wright argued, in other words, that a large population has a greater chance of getting stuck
on some “local optimum” than a series of smaller populations, whose subdivisions allow
for the exploration of alternative adaptive peaks through the action of drift. Once a high
peak is found by a subgroup, its members will thrive and invade the other subgroups of
the population. In this way, the overall population comes to occupy a high peak, in a way
that would be less likely if selection were acting alone. (See Ridley 1996: 217–219, for
an accessible presentation of Wright’s ideas.)
This shifting balance model was criticized by R. A. Fisher, and is not widely accepted
(Ridley 1996: 219). Even so, population thinking of this sort might lead one to complicate
Diamond’s explanation of innovative success by pointing to the potential trade-off between,
on the one hand, societies that are large enough, conformist enough, and have the right
norms of communication to enable a successful technology to spread rapidly and faithfully
and, on the other hand, societies that are fragmented, prone to errors in communication,
and tolerant enough to allow diverse experiments that will prevent convergence on local
technological optima.
One could use this kind of model to fashion an answer to the so-called Needham Ques-
tion (Needham 1975). This is the question sometimes asked by historians of science and
technology of why China lagged behind the West in the period when Europe was enjoying
great technical and scientifi c creativity. Perhaps Wright’s shifting-balance model could
inspire a novel populational answer, in terms of the subdivided nature of Europe compared
to the national unity of China. Perhaps the fragmented nations of Europe permitted a
hedging of innovative bets not possible in the more monolithic China, while international
trade allowed successful techniques developed in one European nation to spill over into
others.
This is indeed a hypothesis worth testing, but it does not show decisively that population
thinking has heuristic value. David Hume used more intuitive forms of thinking to arrive
at a very similar hypothesis some time ago. Hume claimed:
That nothing is more favourable to the rise of politeness and learning, than a number of neighbour-
ing and independent states, connected together by commerce and policy. The emulation, which natu-
rally arises among those neighbouring states, is an obvious source of improvement: But what I would
chiefl y insist on is the stop, which such limited territories give both to power and to authority. (Hume
1994 [1742]: 64)
Hume goes on to explain the contrast between Europe and China, kicking off with a
diagnosis of what the Greeks got right:
Greece was a cluster of little principalities, which soon became republics; and being united both by
their near neighbourhood, and by the ties of the same language and interest, they entered into the
closest intercourse of commerce and learning. There concurred a happy climate, a soil not unfertile,