The Tuatha'an said:
How do you explain the genetic simliarities between animals?
A caveat is in order. Biological similarities
by themselves are not a very strong argument for evolution, but the
patterns of similarities we see--yielding the infamous double-nested hierarchy of life--
are.
You can classify pretty much anything into a hierarchy, but only
evolutionary related things into a
double-nested hierarchy. For example, if you take several computer systems or cars, both
specially manufactured things, you can classify them by speakers (attached to/separate from monitor), motherboard brand, processor speed, amount and type of RAM, graphic card, etc. Each of the classification schemes will result in a different final order.
On the other hand, you can classify
animals on the basis of a wide variety of features, and the classification will be more or less the same regardless of
which features you base it on. Humans will
virtually always be closer related to apes, than say to invertebrates
despite the comparison method used. In sharp contrast, Computer A will be much closer to Computer B, Computer C, Computer D, etc.
depending on which classification scheme you opt for.
This occurs because when something is
specially created, modular reuse of components is inevitable. A designer is not limited by evolutionary history--He could freely mix and match components from a wide variety of designs, resulting in a hodgepodge of possible classification schemes.
Evolutionary processes, however, cannot mix-and-match intelligently and independently. If something develops in the mammal lineage once it's split from reptiles, it's not gonna spontaneously appear in the reptile lineage.
This only applies to complex features, of course. Analogies, like different
types of flight, can develop independently, but you'll never find
the same complex feature, down to little details, appear elsewhere than its patron lineage.
To put it simply, if we found a bird with pterosaur wings, or a whale with shark gills, or any of a wide variety of possible chimeras that are perfectly plausible creatures yet violate the limits evolution allows for, the theory is toast. But we don't. Each and every lifeform we've ever studied, barring those engaged in demonstrable horizontal gene transfer (which is
the bacterial equivalent of mix-and-match, since they actually
do exchange components freely), has been consistent in this regard.
This line of evidence really shines when correlated with the fossil record. It lets us predict, for example, that organisms with traits shared between X and Y lifeforms (say, reptiles and mammals)
appeared earlier than either in the geologic record. Inevitably, these unlikely (from a creationist perspective) predictions come true with the discovery of fossils that are proto-mammalia, yet similar to reptiles, for examples. And this insight into past history of life on earth is possible merely from studying
modern animals,
which shouldn't be if they're unrelated and hence have no traces of ancient history in their very anatomy and genetics to be studied!
The same thing, FYI, is used in regard to Biblical research and history in general. The criterion of multiple attestation, which says a tradition independently attested in more than one source goes back earlier than both authors wrote, is a prime example of evolutionary insights applied to Bible studies. Quite ironic, wouldn't you agree? ;)
--Silver
