Comparing the anatomy of one kind of animal with another is supposed to prove descent from a common ancestor. This is often put forward as strong evidence for evolution. However, the science of comparative anatomy can just as easily be used as evidence of creation.
The bones of a horse are different from our bones, but there is such a similarity that if we are familiar with the human skeleton, we could easily identify and name the bones of a horse. We could do the same if we studied the skeleton of a salamander, a crocodile, a bird, or a bat. However, not only are the bones similar, but so also are other anatomical structures, such as muscles, the heart, the liver, the kidneys, the eyes, the lungs, the digestive tract, and so on. This is interpreted by the evolutionists as proof that these various animals are all descended from a common ancestor.
One of the classic examples that is often used in biology textbooks to illustrate comparative anatomy is the forelimbs of amphibians, reptiles, humans, birds, bats, and quadrupeds. In the illustration, it can be seen that all the forelimbs of these six different types of creatures have an upper arm bone (the humerus) and two lower arm bones (the radius and the ulna), although in the case of the bat there is only one bone, called the radio-ulna.
Evolutionists teach that these structures are said to be homologous when they are similar in structure and origin, but not necessarily in function. But notice how subtly the notion of origins is introduced into the definition. The bat’s wing is considered to be homologous to the forelimb of a salamander because it is similar in structure and believed to have the same origin. However, it is not considered to be homologous to the wing of an insect because, even though it has the same function, it is not considered to have the same origin. However, the fact that the two structures are similar does not necessarily mean that they are derived from a common ancestor.
We have to realize that the entire line of reasoning by evolutionists is based upon a single assumption: that the degree of similarity between organisms indicates the degree of supposed relationship of the said organisms. In other words, it is argued that if animals look alike, then they must be closely related (from an evolutionary point of view), and if they do not look very much alike, then they are more distantly related. But this is just an assumption.
The presence of homologous structures can actually be interpreted as evidence for a common designer. Contrary to the oversimplified claim in this figure, the forelimbs of vertebrates do not form in the same way. Specifically, in frogs the phalanges form as buds that grow outward and in humans they form from a ridge that develops furrows inward. The fact that the bones can be correlated does not mean that they are evidence of a single common ancestor.2
In fact, there is another logical reason why things look alike—creation by an intelligent designer using a common blueprint. This is the reason that Toyota and Ford motor vehicles look so much alike. They are built to a common plan—you only have to look at them to realize this. However, the problem with the living world is that in many cases either explanation (i.e., evolution or creation) appears to be logical and it is often impossible for us to tell which is the more reasonable explanation. This is why it is important for us to understand which worldview we are using to interpret the evidence.
There is, however, one discovery that appears to make the evolutionary view of descent from a common ancestor look illogical and flawed. This discovery is that structures that appear homologous often develop under the control of genes that are not homologous. If the structures evolved from the same source, you would expect the same genes to make the structures. The fact that these structures are similar (or homologous) is apparent, but the reason is not because of Darwinian evolution. It is more logical and reasonable to believe in a common Creator rather than a common ancestor.
Many evolutionists readily admit that they have failed to find evidence of the evolution of large structures such as bones and muscles, so instead they argue that they have found homology among the complex organic molecules that are found in living systems. One of these is hemoglobin, the protein that carries oxygen in red blood cells. Although this protein is found in nearly all vertebrates, it is also found in some invertebrates (worms, starfish, clams, and insects) and also in some bacteria. Yet there is no evidence of the evolution of this chemical—in all cases, the same kind of molecule is complete and fully functional. If evolution has occurred, it should be possible to map out how hemoglobin evolved, but this cannot be done. To the creationist, however, hemoglobin crops up complete and fully functional wherever the Creator deems it fitting in His plan.