R.C. Steward found a correlation between melanism and the concentration of sulfur dioxide (an airborne pollutant) north -- but not south -- of latitude 52 degrees north.The assertion that Steward found no correlation between melanism and the concentration of sulphur dioxide south of latitude 52 degrees north is simply false. The correlation which Steward (1977) found between the proportion of dark moths and the concentration of sulphur dioxide (or, more accurately, its square-root) was highly significant both over England and Wales as a whole, and south of latitude 52 degrees north.
in the south of Britain non-industrial factors may be of greater importance in determining carbonaria frequency than in the rest of Britain (1977, 239).But his reasoning here is hard to follow. In the midlands and north of England, most of the major industrial centres are located towards the west, whereas in the south they are located in the east, near London. In the south-west, the counties of Somerset, Dorset, Cornwall and Devon are among the least polluted in the whole of England and Wales. Moreover, in the north and midlands the prevailing south-westerly winds carry airborne pollution long distances towards the east. It is therefore hardly surprising, if Kettlewell's explanation is valid, that the proportion of dark moths correlates more strongly with east-west location and less strongly with sulphur dioxide concentration in the south than it does in the north.
Steward concluded that "in the south of Britain non-industrial factors may be of greater importance" than camouflage and bird predation.This clearly misrepresents the quoted statment of Steward's as referring to a comparison of non-industrial factors with camouflage and bird predation, whereas his actual comparison was between non-industrial factors in the south and those same factors in the north.
The results suggest that, although selective predation may have an important secondary effect on carbonaria frequency, it is not the major factor determining frequencies at these sites."These sites" here refers to 52 sites, of which 48 were located south of latitude 52 degrees north, where Steward had studied the effects of camouflage on rates of predation. Also, "the results" being referred to are those from this study of the effects of camouflage, not those from the study of correlation between melanism and other variables.