The Logarithmic Spiral of the Nautilus
The nautilus shell is perhaps nature's most perfect example of the logarithmic spiral. As the cephalopod grows, it creates larger chambers, but the shape of the shell remains constant.
Polar Equation: $r = ae^{b\theta}$
This means that for every equal increment of the angle $\theta$, the distance from the origin $r$ increases by a constant factor. It allows the organism to grow without changing its center of gravity or overall proportions—a brilliant piece of biological engineering.