The Environmental Security Hypothesis says that in tough times men will prefer women who are good at production, generally older, taller, heavier, less curvaceous women with less body fat. In good times, they will prefer women who are good at reproduction, generally younger, shorter, lighter, more curvaceous women. Pettijohn and and Jungeberg look at the characteristics of playboy playmates from 1960 to 2000 and find:

Consistent with Environmental Security Hypothesis predictions, when social and economic conditions were difficult, older, heavier, taller Playboy Playmates of the Year with larger waists, smaller eyes, larger waist-to-hip ratios, smaller bust-to-waist ratios, and smaller body mass index values were selected. These results suggest that environmental security may influence perceptions and preferences for women with certain body and facial features.

Econometricians who wish to investigate further may download the data here (yes really). The 2008 Playmate of the year, Jayde Nicole. does not seem to fit the hypothesis however.