"Mollusks and vascular plants account for more than 80 percent" (Futuyma 87) of the world's species, with about "1.4 to 1.8 million species" (Futuyma 87) in all.
Changes occur in living organisms to help increase their adaptability, or potential for survival and reproduction, in the face of changing environments. Evolution apparently has no built-in direction or purpose. A given kind of organism may evolve only when it occurs in a variety of forms differing in hereditary characteristics, or traits, that are passed from parent to offspring. By chance, some varieties prove to be poorly adapted to their current environment and thus disappear, whereas others prove to be adaptive, and their numbers increase. The elimination of the unfit, or the "survival of the fittest," is known as natural selection because it is nature that discards or favors a particular variant. Basically, evolution takes place only when natural selection operates on a population of organisms containing diverse inheritable forms. .
Creationists have gone back to the basic laws of nature to see if evolution is physically possible given enough time and opportunity. The one major problem that they see is the 2nd Law of Thermodynamics. It states, "All natural systems degenerate when left to themselves". This is why everything falls apart and decays over time. Creationists point to death as being the ultimate manifestation of this law. This physics principle does not allow for something as complex as the human eye to originate from something simple. The eye must follow the tendency for complete degeneration. Creationists see a downward spiral for every living and non-living creation. Everything breaks down into simpler substances; they do not become more complex. Creationists say that, in the real world the long-term flow is downhill, not uphill. An experimental and physical observation appears to confirm that the law is indeed universal, affecting all natural processes in the long run.
