Page 158 - Engineering in Nature

Engineering in Nature

This force is also present when you place your hand on the wall,
but it is very weak. If you were to view your hand at the atomic level,
you would see that its surface is covered in tiny crests, and only the
few atoms at the tops of these crests make actual contact with the
wall. However, the thousands of spatulate tips on the gecko's feet
stick to the wall with greater force.
If the gecko's toes really were covered with an adhesive (or with
suction caps, as scientists once believed) then every time it lifted its
feet the lizard would have to expend considerable energy to break
that adhesion. According to the findings of the research team, howe-
ver, in order for the gecko to lift its feet, it needs only to change the
angle at which it makes contact with the wall. 48
The position and concentration of the micro-hairs on the gecko's
feet give rise to the Van der Waals Force, which overcomes the force of
gravity. When it wishes to take another step, the reptile bends the sole
of its foot forward and raises it by expending a greater molecular
force than that of gravity. 49
Clearly, the number and angle of the hairs on the creature's feet are
based on sensitive engineering. Were the density of the hairs any
greater, the animal would stick to the ceiling; any less, or if the hairs
were located at a different angle, it would fall off.
Yet such a thing never happens. The density of the hairs that give
rise to the Van der Waals force is exactly right.
If a gecko that had 2,000 hairs per square millimeter instead of 2
million, an insufficient Van der Waals force would form, and it would
fall off as it attempted to walk on the ceiling. The existence of the
whole elaborate hair structure would be to no avail.

The Coordination in the Gecko's Feet
In addition to all this, the gecko lizard must also enjoy perfect co-

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