One of the most commonly used evidences for Darwinism is the fact of morphological similarities between various organisms. To put it simply, many organisms look like each other. These similarities extend not just through the physical phenotype, but also into the genotype as well. Indeed, much hay is made over the fact that chimp DNA is 98% similar to human DNA (although that figure has been questioned recently).
Rather than looking at some specific examples, I want to first look at the concept as a whole. Is it true that morphological similarities imply common descent from an original species?
It is certainly true that similarities can indicate descent. We see examples of this in the genome all the time, especially with recessive and dominant genes that obviously follow a hereditary tree. But we have equal evidence of similarities that do not follow heredity, that do not imply common descent.
One obvious example of this is found if you look in the parking lot at your local mall. You will see various “organisms” of vehicles out there: Ford, Chevy, Nissan, Mazda, etc. All of these vehicles have similar structure, are made from similar materials, and are used in similar manners. Yet we know that the Chevy did not evolve from Ford except insofar as the design was copied by an intelligent agent. As a result of this simple concept, we see that morphological similarities need not imply common descent; they can also imply design.
And we do not need to restrict ourselves to non-biological aspects to see this. Ernst Mayr, for instance, argued that eyes evolved independently over 40 times in the fossil record. That is, eyes formed in various species in the fossil record after the theorized branching point between the two species had already occurred, which is to say that both daughter species came from a common ancestor that was blind, yet both developed eyes anyway. Further evidence is found in the concept of Convergent Evolution, which states (for example) that all birds have the same basic wing shape because it is necessary for flight, not because they all share a common ancestor. In other words, convergent evolution of the wing shape, of eyes, and of myriad other aspects are already acknowledged by Darwinists to not be evidence of common descent, but instead of common use.
Because morphological similarities need not be evidence of common descent (as evidenced by the convergent evolution theory) and they can be evidence of common design (as seen in a myriad number of intelligently designed machines that look alike in order to perform a specific similar function), morphological similarities do not imply common descent. At most, all a Darwinist can say is that morphological similarities are consistent with Darwinism; but the intelligent design advocate can make the same claim about I.D. As such, this often offered argument for Darwinism proves nothing.