Because "common design" and "common ancestry" produce *very* different types of characteristic similarities *and* differences.
There are very specific kinds and patterns of similarities, *and* differences, along multiple independent and cross-confirming lines of evidence, which overwhelmingly support evolutionary origins. See this link if you want to start delving into the details, but the short form is that evolutionary processes would produce *very* specific kinds of similarities across lineages, and *very* specific kinds of differences -- patterns which would *not* be produced by "design" processes, unless the designer was being intentionally deceitful and purposely mimicking the byproducts of evolution. And those evolutionary patterns are exactly what we find when we analyze DNA, at every level, in every genome, in every way we've thought to test so far, hundreds of thousands of times over.
This is not some mere coincidence or loose "similarity". This is a rich, deep, detailed history of evolutionary "tracers" which are embedded in every genome in hundreds of conceivable ways.
It's no overstatement to say that to any objective observer who has taken the time to actually view and understand the DNA evidence, the debate over whether life on Earth evolved through common ancestry is *over*. The evidence is just vastly overwhelming that it did.
If you're unclear as to how science actually tests its analyses of the evidence to ensure that they are valid, see this post. This post also covers, in general, how common descent is distinguished from design hypotheses when testing the evidence.
Furthermore, people often use a programming analogy, it should be pointed out that no one could possibly mistake the results of "evolutionary programming" (like genetic algorithms, etc., whereby evolution is harnessed to produce program code without direct human intervention or programming) for the results of a program written directly by a programmer (i.e. "designer"), even one which incorporated a lot of "code re-use" or cut-and-paste from other projects.
The results of the two methods of producing programs are *vastly* different in character and structure, and any programmer could tell at a glance whether a particular program was actually written by a human, or "grown/evolved" via genetic algorithms. And the same goes for DNA -- it looks exactly like the results of an evolutionary process, and not at all like the results of a "design team".
You speak as though you can say, with authority, that you have observed examples of both "common design" and "common ancestry" and therefore can accurately distinguish between the two.
But, that is begging the question. How can you know (when you study and observe a given set of organic beings) that you are looking at an example of common ancestry as opposed to an example of common design?
You have already ruled out "common design" (because it doesn't fit your evolutionary preconceptions). In your view, common design simply never occurs because you have already decided beforehand that no Designer exists. That only leaves the other option (the only one you will accept) which is common ancestry. So I guess no matter what species we are talking about or looking at, we all know that we shall see the idea of common ancestry "proved".
Ichneumon, Ichneumon...I have skimmed over the lengthy post #76 that you referred to in one of your previous posts. No doubt, it seems impressive, and I freely concede that I do not have the background in these fields of study, not to mention the sheer time it would take, to explore all of the citations, articles, ad nauseum that you list there.
However, it is not necessary for me to go on a fruitless quest to understand the minute details of everything that evolutionists allege in their papers and articles. That would be a tremendous waste of time and energy. The crux of the matter is that it still boils down to some basic questions that must be dealt with up front.
Setting the philosophical questions aside, the two biggest problems for the evolutionists are the absence of transitional fossil forms and the blind-faith assertion that macroevolution has occurred.
Here is a link from True Origins which deals exhaustively with macroevolution. I could see just by the link titles on this page that it deals with many of the issues your post 76 referred to.
http://www.trueorigin.org/theobald1a.asp
Beyond that, there is the basic philosophy of atheism/agnosticism which drives the evolutionist. There are some quotes here which will surprise you. Here is an article from the Answers In Genesis website. Note especially the quotes from Michael J. Behe:
Biblical claim: We are able to recognize evidence of design (intelligent input) when we see it (e.g., Mt. Rushmore, a watch). The evidence of design in the creation is also apparent and implies there is a Designer.
Secular counter-claim: Things have evolved to fit their environment, so of course they will appear “designed.”
The molecule of heredity, DNA, contains the information necessary to build life. Where did the information come from?
The biochemical machines necessary to “read” the information on DNA are also built by the information on the DNA. Both must be in place from the beginning in order to function properly.
Information scientists have found that information and code systems cannot arise from matter on their own, but must be organized by an intelligent source, ultimately. God, infinitely intelligent, is the source for the information and code systems necessary for life.
The evolutionists who deny God have a blind faith—they have to believe something that is against real science—namely, that information can arise from disorder by chance. The Christian faith is not a blind faith, but is logically defensible, and explains the findings of real science.
Quotes
Carl Sagan, Cosmos, p. 4, 1980. The cosmos is all that is or ever was or ever will be.
Richard Dawkins (a vehement atheistic evolutionist), The Blind Watchmaker, W.W. Norton & Co, New York, p. 43, 1987. We have seen that living things are too improbable and too beautifully designed to have come into existence by chance.
Michael J. Behe, Darwin’s Black Box, The Free Press, pp. 252–253, 1996. Now it’s the turn of the fundamental science of life, modern biochemistry, to disturb. The simplicity that was once expected to be the foundation of life has proven to be a phantom; instead, systems of horrendous, irreducible complexity inhabit the cell. The resulting realization that life was designed by an intelligence is a shock to us in the twentieth century who have gotten used to thinking of life as the result of simple natural laws. But other centuries have had their shocks, and there is no reason to suppose that we should escape them.
Michael J. Behe, Darwin’s Black Box, The Free Press, p. 243, 1996. The fourth and most powerful reason for science’s reluctance to embrace a theory of intelligent design is also based on philosophical considerations. Many people, including many important and well-respected scientists, just don’t want there to be anything beyond nature. They don’t want a supernatural being to affect nature, no matter how brief or constructive the interaction may have been. In other words, like young-earth creationists, they bring an a priori philosophical commitment to their science that restricts what kinds of explanations they will accept about the physical world. Sometimes this leads to rather odd behavior.
Werner Gitt, In the Beginning was Information, CLV, Bielenfeld, Germany, pp. 64–7. There is no known natural law through which matter can give rise to information, neither is any physical process or material phenomenon known that can do this.
Richard Lewontin (Harvard Geneticist), Billions & Billions of Demons, The New York Review of Books, p. 31, Jan. 9, 1997. Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door. (Emphases in original.)
San Diego Union-Tribune, November 5, 1993. Some speculate that alien intelligence might beam vast streams of coded information, a virtual encyclopedia galactica, with insights into the origin of the universe or immortality.
Carl Sagan, The Cosmic Connection: An Extraterrestrial Perspective, Anchor Press, Doubleday, p. 224, 1973. At this very moment the messages from another civilization may be wafting across space, driven by unimaginably advanced devices, there for us to detect them—if only we knew how. Or perhaps the messages are already here, present in some everyday experience that we have not made the right mental effort to recognize. The power of such an advanced civilization is very great. Their messages may lie in quite familiar circumstances. The message from the stars may be here already. But where?
Charles Darwin, The Morality of Evolution, Autobiography, Norton, p. 94, 1958. A man who has no assured and ever-present belief in the existence of a personal God, or of a future existence with retribution and reward, can have for his rule of life, as far as I can see, only to follow those impulses and instincts which are the strongest or which seem to him the best ones.
Jeffrey Dahmer (serial murderer) in an interview with Stone Phillips, Dateline NBC, November 29, 1994. If a person doesn’t think there is a God to be accountable to, then—then what’s—what’s the point of—of trying to modify your behavior to keep it within acceptable ranges? That how I thought, anyway. I always believed the theory of evolution as truth, that we all just came from the slime. When we died, you know, that was it, there is nothing … .
Here is a link which is one of many from Answers In Genesis that describes the problem with transitional fossils:
http://www.answersingenesis.org/Home/Area/re1/chapter3.asp