Our dataset on shell polymorphism in Cepaea nemoralis is unique among genetic studies of non-human organisms for its combination of wide geographic scale, deep historical scope and the large number of individuals scored. By combining habitat, climate, and geographic variables in spatially-informed models, we have obtained a comprehensive picture of evolutionary change over the recent period of anthropogenic global change. The time elapsed between the heavy sampling of C. nemoralis in the 1960s and '70s and our major sampling effort in the Evolution MegaLab is 40–50 years, or about 15–20 Cepaea generations. We hypothesized that the increase in environmental temperature that occurred towards the end of the twentieth century would have favoured shell morphs with a higher albedo. Although we did detect evolutionary changes, those found in our most comprehensive analyses were either not in the direction predicted or they were uncorrelated with local temperature change and so did not support our hypothesis.
The cline in the frequency of the Yellow morph known from the historical period 
persisted into the 21st Century (). In the full statistical model, the Yellow morph decreased slightly in frequency over time, but only at a marginal level of significance (P
0.036, ). If a warming climate had driven an increase in the frequency of Yellow, a correlation between the two variables in the full model could hide an increase in Yellow. If this was the case, then removing temperature from the model ought to reveal any increase in Yellow that had actually occurred. However, when we dropped temperature from the model, Yellow was found not to have changed at all. The paired sample analysis, which utilized a small subset of our data comprising only about 10% of all samples, found an increase in the frequency of Yellow in dunes, but not in the other three habitat types ().
This difference between sand dunes and the other habitats which provide more vegetation cover may provide a clue as to why the expected increase in Yellow was not general. Behavioural and physiological adaptation to temperature can buffer evolutionary responses to a warming climate 
. Behavioural thermoregulation occurs in Cepaea
and varies between morphs 
, but snails require shaded refuges into which they can move if this behaviour is to be effective. Such refuges are more available in woods, hedges and grassland than in sand dunes, and this may explain why only in sand dunes was there an increase in the frequency of Yellow morphs. It would also explain the increases in frequency of Yellow with decreasing shadedness of habitat in the order wood<hedge<grass<sand dune ( & ).
Two evolutionary changes in banding, controlled by two different, unlinked loci, were detected. The frequency of Unbanded decreased over time in the complete dataset (), though this change was absent or reversed in the paired sample analysis (). The frequency of Mid-banded (among banded) increased in the dataset as a whole () and among the 245 paired samples taken from hedges (). The magnitude of these frequency changes is better estimated from the models than from changes in raw average frequencies since the models allow for different geographic distributions of sampling points in the historical and modern data sets that could bias raw averages. The models estimated a 10% decrease in Unbanded and a 5% increase in Mid-banded had taken place. The 10% decrease in Unbanded is a surprisingly large change to observe in only 15–20 generations and may be an over-estimate. The 5% increase in Mid-banded is a more robust estimate as change of the same order was also found in the paired-sample analysis of hedge populations ().
Bands are darker than the ground colour of all shell phenotypes and therefore a general decrease in Unbanded (and a corresponding increase in banding) does not support the climate warming hypothesis because this predicts that phenotypes with lower albedo ought to decrease. The increase of Mid-banded, which took place at the expense of morphs with more bands, was in the direction expected from the climate hypothesis and so we applied an additional test. If the climate hypothesis is correct, then the increase in Mid-banded should have been greatest where the temperature increased the most. Our test for this was based upon model predictions and showed that the change in Mid-banded frequency did correlate with local changes in temperature, but that the correlation was negative rather than positive and therefore in the wrong direction to support the hypothesis. The climate hypothesis is therefore not supported and we must look to another explanation for why the frequency of Mid-banded has increased.
Turning to the association between morph and habitat, a strong inference from earlier work was that open habitats have higher frequencies of Yellow and banding than woodland. This observation was made in a mature agricultural region of England 
, where Mid-banded also declined from woods to open areas. A review of results from several studies 
confirmed the colour and banding associations, though the Mid-banded effect was not consistent. In the present analysis () the frequency of Yellow is undoubtedly associated with habitat, increasing from woodland (the most shaded) to sand dunes (the most exposed) (), but with respect to the banding patterns the result with the full data set differs from that recorded earlier for particular locations. Unbanded is lower on sand dunes than in woods and marginally so in hedgerow habitats (). No difference in Unbanded was detected between woodland and grass. Mid-banded was less frequent in dunes than in the other habitats ().
When Cain and Sheppard 
made their original observations they emphasized that woodland samples were darker and more uniform in phenotype than those from open habitats and concluded that this association was due to visual predation tending to increase the match of the samples to their backgrounds. The main predator is the song thrush Turdus philomelos
. However, such an association could also be consistent with a response to microclimate 
. In the modern data the association depends almost entirely on Yellow frequency. The habitat effect may therefore be related to the albedo effect of Yellow that has been revealed on the larger scale, rather than to predation. It should be noted, however, that many ecological changes have occurred between the times of the two surveys, making it difficult to draw general conclusions. Fluctuations in abundance of thrushes must have affected their capacity to exert selection on the snails. Some long-term studies of Cepaea
have recorded vegetational changes coinciding with massive declines in rabbit densities due to myxomatosis 
which must have modified microclimates. Increases in the area of woodland and changes in woodland management have also occurred in Europe over the period of study and these may have been a cause of the increase in Mid-banded due to its lower albedo 
By analyzing data on Cepaea nemoralis
polymorphism and its evolution on a continent-wide scale we have traded the precision of the numerous previous, mainly local studies of this model organism for generality (). In the past, such generalities have been hard to come by in the ecological genetics of Cepaea 
, with much evidence that the forces shaping the evolution of Cepaea
polymorphism can be intensely local and vary from place-to-place. We attempted to deal with some of this spatial variation by including a Location term in our models. This term also allowed for differences in the geographical distribution of samples between the historical and modern datasets and was significant in the models for all three traits (). This result indicates that we successfully captured geographic variation in phenotype frequencies not accounted for by the other variables (altitude, habitat, climate, year). Some of this variation must have included effects such as drift, and the well-known ‘area effects’ found in Cepaea 
that are probably a consequence of founder effects 
The comprehensive data collected by volunteers in the Evolution MegaLab allowed us to apply a powerful test of an evolutionary hypothesis linking climate change with polymorphism in the banded snail. That hypothesis was clearly rejected, but to our surprise, the study also produced another unequivocal result, showing that banded morphs in general and Mid-banded morphs in particular increased. These evolutionary trends do not appear to be related to climate warming and may be related to changing predation pressure by birds. Thanks to the enthusiasm of the general public for bird watching, this hypothesis provides another opportunity for investigation using the power of citizen science.