Darwin's concept of the origin of species by natural selection has been a spectacularly successful and durable scientific theory, but it arguably fails in a basic objective, which is to explain the origins of the qualitative differences of structure between species. Life on earth is described purely in historical terms, with no explanation of how different forms of organisms are generated. This text argues that it is possible to understand evolution as a process that is "pushed" by the intrinsic properties of living matter, rather than "pulled" by natural selection. It shows that seemingly complex structures such as wings or eyes can be built up in a series of simple self-organizing steps, self-organizing in the sense that they arise directly from the chemistry of the developing organism's tissues. In this way, developmental biology acquires the precision of the physical sciences.