Over­weight pond skaters stand no chance on wa­ter


BE­ING over­weight isn’t an is­sue in the world of Pond Skaters.

Peo­ple who keep a gar­den pond or who go dab­bling in wet places are well fa­mil­iar with Pond Skaters, very com­mon wa­ter in­sects that skate grace­fully about on the sur­face of still wa­ter. How they man­age to walk on the wa­ter is amaz­ing.

Wa­ter is made up of units called wa­ter mol­e­cules. It is a fact of phys­i­cal chem­istry that each wa­ter mol­e­cule at­tracts its neigh­bours so there are six at­trac­tive forces at work for ev­ery wa­ter mol­e­cule in the mid­dle of the pond. Each wa­ter mol­e­cule at­tracts its neigh­bour to the right, left, in front, be­hind, above and be­low. While that holds true for all of the wa­ter mol­e­cules in the mid­dle of the pond, those at the sur­face are dif­fer­ent.

Be­cause they are at the sur­face, th­ese wa­ter mol­e­cules ex­ert only five forces: they at­tract their neigh­bour to the right, left, in front, be­hind and be­low but not above for the sim­ple rea­son that there is no wa­ter above them.

The out­come is that the sur­face of the wa­ter is pulled down and side­ways thereby form­ing a rel­a­tively tight skin. While we can eas­ily pierce that skin with our fin­gers, it is tight enough to sup­port the weight of a Pond Skater.

Just as a snow shoe or ski can sup­port a per­son on soft snow be­cause of the in­creased sur­face area, the Pond Skater has evolved to slide around on the side of its legs rather than stand­ing up and walk­ing on the soles on its feet.

The weights that the sur­face ten­sion of wa­ter can sup­port are in a pretty nar­row range so Pond Skaters must have slim bod­ies and long legs to waltz around ef­fec­tively. Fat ones punc­ture the sur­face film and fall prey to preda­tors. Na­ture se­lects those who are fit to sur­vive and se­lects out those who are un­suited.

The obese and over­weight skaters per­ish as in­di­vid­u­als but, more im­por­tantly from a sur­vival per­spec­tive, their demise fil­ters out of the gene poll what­ever genes con­trib­ute to ex­cess weight. The on-go­ing process of evo­lu­tion thereby re­fines the gene pool to pro­duce slim, trim, long-legged in­di­vid­u­als.

Even the slim ones are heavy enough to cause the sur­face skin of the wa­ter to sag un­der their in­signif­i­cant weight as il­lus­trated by the im­age above. Like a per­son skat­ing on thin ice, they live a pre­car­i­ous life. But, hey, that’s what life is all about for a Pond Skater.

Sur­face ten­sion is enough sup­port the weight of a Pond Skater.

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