One of the issues that creationists seem to have the most difficulty with is the concept of natural selection. Weather is one of the strongest selective forces in evolution  – especially long-term changes of either too dry or too wet. Since humans have not lived through such meteorological extremes, those skeptical of evolution doubt its power. Perhaps a more convincing example is needed. Speaking of power, how would you feel if you lived in an environment were a single misstep meant instant death - unless you had a minor inherited variation in your body form that saved you? 
    In the tropical forests of Southwest Asia, there are more gliding animals (frogs, snakes, lizards, geckos) than anywhere else on earth, over 45 species in all. As described in Science 1 anthropologist Nathaniel Dominy of the University of California, Santa Cruz asked - why? He concluded the answer was “rougosity” or the vertical distance to the ground between treetops of different heights. In this setting rougosity is highest when the distance straight to the ground is the greatest. In these forests, most of the plant and animal life occurs in the sun rich canopy at the tops of the trees. Imagine two geckos (like the cute little ones in the Geico insurance ads) sitting on a branch hundreds on feet off the ground. One had a genetic mutation that led him to be born with an excess of floppy skin, the other had no excess skin. They both get distracted and step off the branch and both instinctively spread their legs wide. The excess skin of one allows him to glide safely to a branch 30 feet below. The other plunges to his death.  All of the offspring of the one with excess skin also have excess skin and are protected from sudden death by missteps. All the other geckos without excess skin remain at risk of sudden death. It should surprise no one that after a few dozen generations, all the geckos in this part of the forest were gliding geckos.
    This is an unusually beautiful example of the power of strong selective forces to drive the rapid evolution of new species, in this case 45 new species in one area of the forest. In a later blog I will provide some examples of strong selection for certain genes in humans.


1 Snapshots from the Meeting – Evolution of Gliding  Science 320: 609 (2 May), 2008