The lizard has never had a good press in India. Many communities are very worried about what evil may befall if a lizard from the ceiling falls on our body. Some worry that if it falls on our head, it foretells our early death. If it falls on the toe, there could be physical illness. Indeed, an ancient text called "Gauli Sastra" makes predictions based on where in our body the household lizard falls. Some Hindu almanacs (panchangams) carry excerpts from the above text.
While such predictions are obviously far-fetched, the real wonder is how, in the first place, the lizard is able to climb walls and move on the ceiling upside down. A healthy lizard does not fall off so easily. What makes this tiny animal possess such superhuman ability? This is a poser that has engaged scientists for over half a century. The first thought was that the toes in their feet create a temporary vacuum when they are placed on a surface. But this was proved wrong when the anatomy of their toes was analyzed. Each toe was found to have many thousands of tiny, spatula-tipped split hairs. It is this collective interaction between these hairs and the surface on which the lizard moves that appears responsible for this unusual ability of the animal.
How lizards climb walls
How does it work? This ‘binding’ between the hairs and the surface is very weak in itself. But when thousands of such hairs hit the surface, this tiny electric effect is somewhat enlarged. This induced electric force is termed induced dipole moment. (A real life example is when a child rubs an inflated rubber balloon. She now brings a piece of paper, and finds that the paper can stick to the balloon- thanks to the induced electric field generated upon rubbing, which attracts the paper). A simila induced temporary dipolar force causes the toes to stick on the surface of the wall. And the force is small enough for the toe to overcome the force and take the next step with no trouble, and the lizard moves on, as nimbly as a fashion model does on a catwalk.
This force, caused by such minuscule electrical ‘bonding’ of two substances, and which occurs at very close distances, was first recognized by the Dutch scientist Johannes Diderik van der Waals, and has become known as the van der Waals force. And when this force operates collectively by thousands of toe hairs in tandem, the effect becomes substantial and real-life. In effect then, lizards use the van der Waals forces to climb walls and stay on the ceiling. (Shave their hair off, they may no longer do such heroic acts). It also exemplifies the dictum: in unity and working together is strength.
How they do it
There is yet another superhuman thing that lizards do. Try and catch a lizard by its tail; the tail simply comes off and the lizard scurries away. And a few days later, it regenerates its lost tail! And the lizard is not alone in this act. Its amphibian distant cousins, the salamander and even the frog, can regenerate some of their damaged or lost tissues and limbs. Indeed, a salamander can regenerate its tail, spinal cord, cartilage and some parts of its eye. How do they do these and we humans are not able to? This question has engaged the minds of some scientists from across the globe.
It appears that once a tissue is damaged in the lizard or salamander, many cellular molecules zone in on the damaged or lost site, work on the region to regenerate the relevant cells and coordinate their assembly into the fresh, regenerated tissue. Some of these molecules are related to immunity, some to trigger cell growth and some to redirect the cells to assemble together to form the tissue of interest (cf. TP Lozito and RS Tuan, Lizard Tail Regeneration, Connect Tissue Res. 2017 March, 58(2), 145-154). Another report talks about how normal ‘somatic’ cells can be converted to tissue-regenerative stem cells through the use of two specific molecules (PDGF-AB and AZA; see V. Chandrakanthan et al., PNAS(USA), 2016; www.pnas.org/cgi/doi/10.1073/ pnas.1518244113). Learning from these and similar papers, and attempting to do so with some human tissues are organs would be useful.
Some others have pointed out that the genetic contents (the genome) of the salamander and the human genome have many common genes- some of them with some modifications. Based on this, one scientist has wondered whether “we can awaken the hidden salamander in us”! That is, attempt to find ways to trigger the action of the salamander-like genes in our genome, so that we too may regenerate damaged or lost tissues such as parts of our eyes.
This attempt has been termed as “an audacious goal”. But the very fact a question has been raised would mean people will try to work on the goal, and hopefully in time score some success; after all. Nothing attempted, nothing gained.