Evolutionary naturalism (as taught in American taxpayer-paid public schools) preaches that every living thing came from an unknown, unobserved common ancestor billions of years ago that—conveniently—left no fossil trace.
The best evolutionists can do is to point to studies suggesting this is so, but then insist that evolutionism is a fact and should be dogmatically taught as such.
Recent evolution-based studies suggest that people came from marine invertebrates because we have some genes that are the same as sharks—even though these genes don't code for the same structures:
The same genes that give sharks their sixth sense and allow them to detect electrical signals are also responsible for the development of head and facial features in humans, a new study suggests.
The finding supports the idea that the early sea creatures which eventually evolved into humans could also sense electricity before they emerged onto land.1
On the genetic level, much regarding genes (DNA) is complex and not well understood. Particularly fascinating is how genes interact with each other to activate or deactivate other genes. For example, researchers know of sections of master regulatory genes (e.g., elements of Hox genes) that interact to direct development such as head and facial features. The Creator may very well use similar genes to operate a variety of genetic functions (just as the same switch design can turn on something as different as a motor or a light). This is true whether the genes are in people, sharks, or mice. Darwinists extrapolate, claiming that because the genetic switch is similar, therefore we have an evolutionary connection with these creatures. This is an unscientific leap of faith, but nonetheless must be made by those holding to a secular worldview. Creationists acknowledge the same genetic switch activating the sixth sense in sharks, and face and head development in people. But a similar switch doesn't mean common ancestry. If this were true, the fossil record should document the amusing sea-creature-to-people transition. It does not.
As long as such foolishness is presented as science to the American student (and the public at large), the origins debate in school board meetings nationwide will enjoy top billet.
1. http://livescience.com/animalworld/06020
