Biological traits are products of evolutionary constraints and tradeoffs that make an engineering view essential. But systems shaped by natural selection are fundamentally different from designed systems. They do not have parts with sharp boundaries and specific functions connected in sensible ways. Instead, they are organically complex in ways fundamentally different from designed machines. Tacit creationism is pervasive throughout biology and medicine but it will be hard to purge, because our human minds rebel against the untidiness of organic complexity.