Most of us have been stung by a bee, bitten by an animal, or scratched by a thorny bush. But very few of us have probably taken a close look at nature's painful pointed tips. At first glance, they both look and feel like the cone-shaped needles we know from the doctor's instrument tray. In reality, many natural tips are rounded and curve gently rather than ending in a sharp tip. Mathematically, the shape can be described as the height being proportional to the square of the radius (height ~ radius²). This results in a rounded shape—called a parabola—where the tip is not sharp but gradually becomes steeper away from the center.
Scientists have long assumed that the rounded shape is the result of evolutionary optimization, because it penetrates the skin more easily than a perfect cone, and that organisms have thus evolved their defenses toward the most effective form.
The rounded shape is also more robust, less prone to breaking, and distributes forces more evenly throughout the tissue. But according to Kaare Hartvig Jensen, associate professor at DTU Physics, evolution is likely not the sole explanation for the shape:
"There is a general notion that almost everything in nature exists for a reason. A previous study from 2024 argues that the rounded tips of teeth are due to evolution. But if you look at an unused tooth, it does not necessarily have that shape, and if you observe the shape later in the organism's life, the parabola will emerge. This suggests random mechanical wear. We cannot rule out the role of evolution, but random processes are an equally good explanation."
The researchers' findings were recently published in the renowned scientific journal PNAS in the article 'The geometry of Nature's stingers is universal due to stochastic mechanical wear'.
