Is the Area of the Orbital Opening in Humans Related to Climate?

Objectives: The aim of this study was to evaluate whether climatic conditions impact the size of the anterior orbital opening in humans. The previous research has shown that morphology of the human orbit, a trait strongly related to the shape of the cranium, varies significantly among populations. However, the mechanisms of this variation are still debatable. Besides such evolutionary forces as genetic drift, climatic conditions may be involved. Thermoregulatory processes affect skull shape, and thus may also influence orbital morphology. Methods: A total of 846 dry skulls of male and female adults from three climatic areas (i.e., warm, temperate, and cold) of Europe were evaluated. The areas of the left and right orbital openings were measured using the three-dimensional contact scanner MicroScribe G2L, and analyzed with regard to climate. Results: The results reveal a statistically significant association with climatic conditions on the area of orbital opening in accordance with Bergmann's rule. The anterior orbital opening area was smaller in male individuals from the cold climate, and larger in individuals from the warm climate areas. Conclusions: These data may support the hypothesized association between size of the orbital opening and adaptation to different climatic conditions, but only in males. (C) 2015 Wiley Periodicals, Inc.