The idea of an organism evolving into all creatures as we know them today has been around for centuries. It began with ancient Greek philosophers, and was "rooted in abstract thought" (4) Empedocies officially began the Theory of Evolution, and Thales continued this idea. Thales noticed a small pond with a layer of scum floating on the surface. After hours of observation, he noticed small organisms emerge from the scum, where they eventually grew wings and flew away. We now call these creatures mosquitoes, but Thales called them the origins of life. "When other philosophers looked at the natural world in detail, many drew quite different conclusions" (4).
There are many kinds of changes that take place in organisms that are classified as "evolution." Some of these changes have actually been observed, while others have not. The following are observable forms of evolution.
Micro-Evolution (a.k.a. Change over Time)
--Gradual changes within a kind of animal over several generations. For example, human height has increased due to increased nutrition and health care.
--Offspring will have characteristics of its parents. For example, a child of a Caucasian and an Asian will have characteristics of both parents.Despite the broad definition for Evolution, the term is now understood to mean "Darwinism" or "Neo-Darwinism." This is classified as genetic changes that cause transitions from one species to another. The following have never been observed, recorded, or proven.
--This theory states that all living creatures are modified descendants of a common ancestor. Changes are the result of natural selection acting on random genetic mutations.
-- Gradual change from one kind of animal to another due to helpful genetic mutations.
--This is the theory that evolution happens in steps. For example, "The first bird hatched from a reptilian egg." This theory resulted from the lack of transitional creatures in the Fossil Record, and attempts to account for the sudden, fully formed fossils found that are actually found in the Fossil Record. (More about the Fossil Record on "Fossils" page.)Another Evolutionary Theory is the "Neutral Theory of Molecular Evolution." This theory basically states that mutations are not always harmful, and a cell can build up many of these mutations, then "jump" to a completely new species. This stemmed out of the lack of evidence for Punctuated Equilibrium, and is "about as plausible as the idea of neutral car parts."
Two of the "most widely debated issues in evolutionary theory" are the theories of Vertical Evolution and Cladogenesis. Vertical Evolution, or Anagenesis, states that an animal gradually becomes so different from its original form that eventually a new species is formed, and Cladogenesis states that an original species diverges into several other species.
