Several letters to the editor have stated that macroevolution could work by the same process as microevolution provided it had enough time to occur. I'd like to show why the microevolution mechanism does not apply to macroevolution between species no matter how much time elapses.

      Microevolution is thought to occur by the interaction of mutations (sudden random changes in genes) and natural selection. Natural selection sorts out these random changes according to their value in improving the individual's survival. For instance, variations in finch's beaks derived from habitat changes that made one type of beak better for eating than another or one peppered moth's coloration more advantageous for hiding from predators. These examples of microevolution, supported by scientific method, involve one component of the animal.

      Macro-evolution requires not one but a multitude of changes. Consider flight and sight. It is proposed that flying animals evolved from non-flying animals, such as reptiles to birds. Birds would've had to evolve from cold-blooded to warm-blooded, develop light hollow bones, feathers (an intricate unique system vastly different from scales), and lungs different from those of other vertebrates perfectly integrated with a special circulatory system.

      For eyes to have evolved, there was a time when eyes were nonexistant. In theory, pigment on the skin converged the rays of the sun on that spot, irritating the skin so that a nerve grew, the nerve specialized into retinal cells, the complex visual brain formed, the nerve attached to this optic center of the brain, and there was sight.

      For flight and sight to have evolved, almost every structure in the non-flying and sightless animal would have had to change at precisely the same time, immediately coordinate and integrated. Each structure would have had to be independently and simultaneously adaptive--and they are not. Over 99% of mutations are harmful. Incoordination, under-development or absence of one involved structure would halt the process. The infinity of simultaneous positive changes needed to progress from single-celled creatures to mammals is not supported by the fossil record. The probability of sight and flight from evolution is so low as to render it impossible.

Annie Bukacek MD