In 1985 we resurveyed the sites on the Marlborough Downs in southern Englan
d at which Cain and Currey in 1960/61 sampled Cepaea snails and thence intr
oduced the term 'area effects' to describe large areas of uniform morph fre
quency. Some sites no longer harboured Cepaea and at others the species com
position had changed, with a general spread of Cepaea hortensis at the expe
nse of Cepaea nemoralis. The majority, however, permitted comparison of mor
ph frequencies between the two surveys. In C. nemoralis, we detected a sign
ificant overall decrease in the frequency of the brown morph and estimate s
election as 5-9% per generation. There was no apparent change in frequencie
s of banded morphs. In C. hortensis we detected a significant overall incre
ase in the frequency of unbanded shells (1-3% selection per generation) and
an almost significant decrease in the frequency of fusions within the band
ed class. There was insufficient colour polymorphism in C. hortensis to all
ow analysis of colour morph frequencies. These changes - all in the directi
on of reduced absorption of solar energy - resemble others detected in both
species at other localities in southern England. Possible explanations inc
lude large-scale climatic effects and changes in vegetation. (C) 1998 The L
innean Society of London.