- The validity of evolution and the origins of humanity have often been a subject of great political and religious controversy within the non-scientific community.
- The classification of humans and their relatives has changed considerably over time.
- Speculation about the future evolution of humans is often explored in science fiction as continued speciation of humans as they fill various ecological niches, as well as deliberate self-modification.
Creationists have long argued against the possibility of Macroevolution. Macroevolution is defined by the scientific community to be evolution that occurs at, or above, the level of species. Under this definition, Macroevolution can be considered to be a fact, as evidenced by observed instances of speciation. Creationists, however, tend to apply a more restrictive, if vaguer, definition of Macroevolution, often relating to the emergence of new body forms or organs. The scientific community considers that there is strong evidence for even such more restrictive definitions.
Recent arguments against such restrictive definitions of Homo neanderthalensis macroevolution include the Intelligent design arguments of Irreducible complexity and Specified complexity. However, neither argument has been accepted for publication in a peer-reviewed scientific journal, and both arguments have been rejected by the scientific community as pseudoscience.
11.15.2 Transitional fossils
Transitional fossils are the fossilized remains of intermediary forms of life that illustrate an evolutionary transition. They can be identified by their retention of certain primitive (plesiomorphic) traits in comparison with their more derived relatives. “Missing link” is a popular term for transitional forms.
Critics of evolution say that there are no known transitional fossils. This position is based on a misunderstanding of the nature of what represents a transitional feature. A common creationist argument is that no fossils are found with partially functional features. It is plausible however, that a complex feature with one function can adapt a wholly different function through evolution. The precursor to, for example, a wing, might originally have only been meant for gliding, trapping flying prey, and/or mating display. Nowadays, wings can still have all of these functions, but they are also used in active flight.
Although transitional fossils elucidate the evolutionary transition of one life-form to another, they only exemplify snapshots of this process. Due to the special circumstances required for preservation of living beings, only a very small percentage of all life-forms that ever have existed can be expected to be discovered. Thus, the transition itself can only be illustrated and corroborated by transitional fossils, but it will never be known in detail.
According to modern evolutionary theory, all populations of organisms are in transition. Therefore, a “transitional form” is a human construct of a selected form that vividly represents a particular evolutionary stage, as recognized in hindsight. Contemporary “transitional” forms may be called “living fossils“, but on a cladogram representing the historical divergences of life-forms, a “transitional fossil” will represent an organism at the point where individual lineages (clades) diverge.