You have the cart in front of the horse. They share traits because they share DNA. If you used completely different DNA then they could have completely different traits. Why would a designer need to share traits between separately created species?
We also have the flip side. You could have drastically different DNA and still have the same traits. For example, you could rewrite the anti-codons on tRNA’s which would allow you to have very different DNA sequences that produce the exact same proteins. Talkorigins has a great section on this concept:
One common objection is the assertion that anatomy is not independent of biochemistry, and thus anatomically similar organisms are likely to be similar biochemically (e.g. in their molecular sequences) simply for functional reasons. According to this argument, then, we should expect phylogenies based on molecular sequences to be similar to phylogenies based on morphology even if organisms are not related by common descent. This argument is very wrong. There is no known biological reason, besides common descent, to suppose that similar morphologies must have similar biochemistry. similar morphology and function is not necessarily the result of similar DNA or biochemistry. The reason is easily understood once explained; many very different DNA sequences or biochemical structures can result in the same functions and the same morphologies (see predictions 4.1 and 4.2 for a detailed explanation).
As a close analogy, consider computer programs. Netscape works essentially the same on a Macintosh, an IBM, or a Unix machine, but the binary code for each program is quite different. Computer programs that perform the same functions can be written in most any computer language—Basic, Fortran, C, C++, Java, Pascal, etc. and identical programs can be compiled into binary code many different ways. Furthermore, even using the same computer language, there are many different ways to write any specific computer program, even using the same algorithms and subroutines. In the end, there is no reason to suspect that similar computer programs are written with similar code, based solely on the function of the program. This is the reason why software companies keep their source code secret, but they don’t care that competitors can use their programs—it is essentially impossible to deduce the program code from the function and operation of the software. The same conclusion applies to biological organisms, for very similar reasons.
To reiterate, although similar genotypes (e.g. molecular sequences) often give similar phenotypes (e.g. morphological characters), similar phenotypes are not necessarily the result of similar genotypes. Thus, it is entirely possible that phylogenetic trees constructed from genotypic data could be radically different from phylogenetic trees constructed from phenotypic data. In fact, in the absence of common descent or any other reason to suppose that these two types of trees should be similar, the most likely result by far is that they will be radically different. This is precisely why it is possible to falsify the macroevolutionary prediction that independently derived phylogenies should be similar.29+ Evidences for Macroevolution: Part 1
3 Likes