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Both inside and outside cells, van der Waals interactions are involved in the attraction between molecules involved in biological systems. A particularly remarkable example of van der Waals forces in action in biology is the attachment of a gecko to a wall of glass. Geckos have many tens of thousands of setae – tiny hairs – on their feet, each of which attaches to a surface using van der Waals interactions between the surface and the tiny projections on the setae (Figure 3.14). The combined force is large enough to hold up the gecko and accounts for their ability to attach to a smooth glass surface.

Figure 3.14 Looking at van der Waals forces in action. A gecko attached to a window. The hairs on its feet interact with the surface using van der Waals interactions.

This example is particularly remarkable, since it provides a lucid demonstration of the way in which evolution has homed in on forces expressed at the molecular level to give selective advantage (the ability to run up vertical flat walls) at the scale of the whole organism.