Leading edge Collisions between pencils found that no matter how sharp they were to begin with, their tips always developed a parabolic shape. (Courtesy: John Sebastian, Technical University of Denmark)"> Leading edge Collisions between pencils found that no matter how sharp they were to begin with, their tips always developed a parabolic shape. (Courtesy: John Sebastian, Technical University of Denmark) You might think that a bee’s stinger, a rose’s thorn or a razor-like animal tooth has a sharp pointed tip, rather like “cone-shaped” needles used for injections. Yet a closer look finds otherwise, and these objects are usually rounded at the tip, curving gently like a parabola. Why this is the case is a mystery and it was thought that it was the result of convergent evolution, in other words different species independently arriving at similar solutions. This is partly because a rounded curve penetrates skin better as it distributes forces more evenly throughout the tissue.…