Abstract

In Seasonal Affective Disorder an individual’s mood varies with the seasons such that the sufferer is often ‘up-beat’ in summer, being high spirited and full of energy but, in contrast, depressed in winter with low spirit and lethargy. Today it is considered that much of the population varies in mood with the seasons and that this is associated with latitudes away from the equator (the latitude hypothesis). In order to test this hypothesis we gathered self-reported data from two samples living at two different latitudes (51 N and 35 N). Additionally we examined the relationship between eye colouration and levels of reported mood variability with the seasons. In relation to latitude no significant differences were observed between the samples. With regard to eye colouration, a significant difference was uncovered between blue/light eyed and brown/dark eyed individuals across the samples with the latter self-reporting higher levels of mood variability with the seasons. Results are discussed in terms of the possibility of blue eye colour having evolved to ameliorate the effects of living at latitudes away from the equator with the resultant annual variability in photoperiod.