The present study is based on a large cross-cultural study, which showed that a systemizing cognition type has a high impact on motivation to learn science, while the impact of gender is only indirect thorough systemizing. The present study uses the same structural equation model as in the cross-cultural study and separately tests it for physics, chemistry, and biology. The model was confirmed for physics and chemistry, but not for biology. This is interpreted as empirical evidence for a cognitive difference between the learning of hard sciences (like physics and chemistry) and life sciences (like biology) that reflects an epistemological difference between ordered (linear) and complex (non-linear) systems. It is concluded that a more prominent inclusion of complex issues into science teaching could motivate low and average systemizers, independent of their gender, for science learning, that is, could be a key to science for all. Thus, there is a mutual benefit between important 21st century's issues of science teaching and the need to foster students' motivation to learn science.