The idea of taking inspiration from nature, and in particular from living systems, in the design of technological systems is fairly widespread and originated much research work. However, while in the field of materials this approach allowed the construction of systems of high complexity but at the same time inexpensive and able to be mass produced, the idea that, in a wider context, natural systems are necessarily optimized seems not to be justified. Optimization must not be confused with evolution: after Darwin we understand that there is no finalism in evolutionary processes, and that the mechanism producing the design' of living organisms cannot result in optimal designs to fulfil any given task, but can only cause a continuous adaptation to the environment. Similarly unfounded seems to be the idea that machines and devices, necessarily better that those obtained by using the traditional design approach, can be designed by taking inspiration from nature. The trial-and-error approach, supported by the principles of bionics, represents a setback with respect to the application of scientific principles to technology which so much contributed to the technological advancement in the modern world.