Thursday, July 2, 2009
Okay, first let me define "homologous structures." Bears and humans both have five toes on their their feet (and hands, in the case of humans). This similar arrangement is called a "homologous structure." Such similarities are the study of comparative anatomy, which investigates the arrangements of various animals and tries to determine whether similar structures are a result of ancestry.
One argument for evolution is that all vertebrate animals (animals with backbones--almost every kind of creature we think of as an animal in the common sense) appear to share the same basic bones in their skeletons. Even structures as diverse as bat wings and cougar legs appear to be variations of the same arm bones.
Some animals, such as horses, have very unique limbs and digits. In the case of the horse, there are not five toes, but just one on each foot. However, the rear feet of modern horses have tiny extra toes hidden alongside the main toe bones. Furthermore, horses are sometimes born with three toes, and early fossil horses had up to five!
Creationists explain these homologous features by suggesting a designer could have simply used the same basic "plan" when designing all the animals. Four legs, one upper arm bone, two lower arm bones and five fingers was just the blueprint used by the designer.
The problem with this argument is that no real designer ever restricts themselves in this way. Imagine if airplane designers began every blueprint for airplanes with the frame of a car. And cars frames were simply enlarged, stretched out versions of bicycles, and so on back to wagons. This is simply not how designers work. This is how heredity works!
You look like your parents because you're related to your parents. Animals share skeletal arrangements because they are related to one another.
Again, human designers were not foolish enough to restrict themselves to a single template for their designs. Why would we expect a supernatural designer to do so?
And if you say, "well some early car designs were based on wagons, and some rocket ships borrowed from aircraft designs," you are either missing the point or being disingenuous. Humans do sometimes borrow from other objects when they design something new, but we do not see a single template arbitrarily applied across the breadth of human designs. Again, vertebrate animals all share the very same template from fish to birds to humans. This is not a mark of design.
Posted by David Board at 1:02 AM