Design for function is even more important than design for appearance. It is also a fascinating pursuit which brings delight and challenge to engineers and others who engage in it.

Living organisms are examples of design strictly for function, the product of blind evolutionary forces rather than conscious thought, yet far excelling the products of engineering. When the engineer looks at nature he sees familiar principles of design being followed, often in surprising and elegant ways. Sometimes, as in the case of flight, he is inspired to invention: more commonly, he discovers his ideas are already embodied in some animal or plant.

This book is about design for function, and invention, which is the grandest form of design, in both engineering and nature. It draws out general principles, and shows how similar problems have led to similar solutions, both millions of years ago in the course of evolution and by engineers in our own time. In arctic animals, heat is conserved in an elegant way which we use in making steel and in gas turbines. The helical alignment of muscle fibres in fish puzzled biologists, but is now seen to have much the same role as the helical lay of the strands in a rope. The function of the alula, the small winglet springing from the leading edge of some bird wings, is still not fully understood but is probably basically the same as that of the Handley Page slot which was invented to delay stall in aircraft wings.