Holly leaves aren’t just festive—they’re smart. The holly plant (Ilex aquifolium) can change its leaf shape to protect itself from hungry animals like deer. Lower branches grow sharp, spiny leaves that deter nibblers, while higher branches, out of reach, have smooth, spine-free leaves.

This shape-shifting defense is a real-life example of epigenetics—changes in gene expression triggered by the environment. When herbivores are nearby, the plant “switches on” genes to grow spines where they’re most needed.

Even more impressive? A single holly tree can have both smooth and spiny leaves at the same time, depending on the threat level. It's a clever survival strategy written in flexible biology.