Fig. 2

Percentage of correct and incorrect pressure use in gain and loss items. Students spontaneously (i.e., unprompted) utilized pressure concepts as a component of evolutionary explanations in both gain and loss contexts. Within the context of evolutionary gain, such as the gain of acorns in oak species, 21.5% of students used pressure in their responses. In the context of evolutionary loss, such as the loss of thorns in a rose species, pressure responses constituted 12.4% of the total responses. The majority of student explanations using “pressure” were judged to be incorrect