Saturday, March 12, 2005
Some Comments on Homology
What is Homology
Homologous limbs are limbs or organs shard between species that have a large number of features in common. These differ from analogous structures, which are limbs or organs which have a similar function, but much different features.
For example, the wings of birds and bats are analogous -- they both accomplish flight but share few structural similarities. The structure of vertebrate forelimbs are usually homologous, because even if their use is different, the structure is very similar.
Evolutionists believe that homology provides great evidence of evolution. They believe that the shared structure indicates a common parentage. They believe that shared structure of limbs performing vastly different functions shows evolution especially well, because it indicates that a given structure was being re-used. The idea is that a designer would have created more specialized structures rather than re-using similar structures for different purposes. The use of similar structures for different purposes is evidence of adaptation to differing environments. Since evolution requires very stable intermediates even in the fastest evolution, it requires that many structures remain shared and simply repurposed in different environments.
This is fairly good evidence for evolution. However, when weighing the evidence, one must also weigh the counter-evidence. For homology, the counter-evidence would be homologous structures that are outside the expected evolutionary tree. The more similar the homology and the further diverged from the evolutionary tree (especially when diverged from the environment that supposedly gave rise to the structure in the first place) the weightier the evidence against evolution. If homologies are continually found outside the expected evolutionary tree, then it can't be said that homologies provide evidence for evolution.
So, instead of examining the evidence, homologies have simply been redefined within biology. The definition of homologies have changed to be similar structures that are a result of common ancestry, while analogies are modified to also include similar structures that are not a result of common ancestry. Notice that, with the new definition, it is logically impossible to have a homology that doesn't prove evolution. This is why evolutionists can consistently say "all the evidence points to evolution" -- because all of the terms have been redefined to assume evolutions existence. The weight of evidence is simply weighed against consistency with the theory of evolution in order to determine its importance.
For the rest of the blog entry (and probably as long as this blog remains active) we will use "homology" and "analogy" to mean the classic definitions of homology and analogy, and "evolutionary homology" to refer to the redefined homology term.
What Do Homologies Indicate?
The crux of the matter is "what, exactly, do homologies indicate?" Unless all homologies or nearly all homologies lined up perfectly with evolutionary homologies, the existence of homologies means very little by itself. Homologies can be explained just as easily by all of the following:
- Common ancestry
- Common designer
- Common pattern of design (with either one or multiple designers)
- Common environment
The common argument from evolutionists is that evolutionists have been able to arrange fossils (especially vertebrate fossiles) in a near-perfect evolutionary tree. This is seen as conclusive proof that evolution must be right -- otherwise no such arrangement would be possible. This argument is patently false. There are many counterexamples. Here are a few:
- Cars can be easily arranged into an "evolutionary hierarchy". However, the similarities between cars is a product of the market (common environment) and the manufacturer (common design) and just the way that cars tend to be built (common pattern of design). We know that automobiles were created, not generated spontaneously or descended one from another, and yet they fit neatly into an evolutionary hierarchy.
- Marvin Lubenow gives an excellent story about how an evolutionary teacher of his gave each student a packet of about 150 metal artifacts (screws, paperclips, etc.) and had the students arrange them in an evolutionary tree. Even though each student's arrangement varied slightly, they all agreed generally. This was supposed to be an exercise in evolutionary classification, but it really showed that any assortment of items can be arranged in an "evolutionary tree" whether or not such a tree is valid.
Are There Counterexamples to Evolutionary Homology?
The answer is an emphatic yes. Of course, as dogmatic evolutionists insist they are the only game in town, they have renamed counterexamples so that they at least appear in name to be consistent with evolution. That name is convergent evolution. While occasionally used to indicate analogous organs, "convergent evolution" is usually used to indicate homologies which do not line up with the evolutionary tree. Examples of convergent evolution are abundant, both morphologically (dealing with the structure of organisms) and biochemically (dealing with the proteins, enzymes, and DNA in the cell). We'll cover a few here.
But first, let's take note of why evolutionists don't think that convergent evolution is a problem for them. They believe that there are perfectly valid explanations other than evolution for homology. The main one they point to is environmental selective pressures which select the same mutations across two lineages. There are a number of problems with this stance:
- If evolutionists agree that there are other possibilities for the origin of homologies than common descent, then they should also agree with us that this makes the use of homologies as evidence of common descent null and void, since homology can be just as much evidence of other mechanisms.
- The idea that the same set of beneficial mutations can occur randomly twice is astronomically low. First of all, the chances of getting one beneficial mutation is astronomically low. The chances of finding a sequence from point A to point B with all containing beneficial or at least non-lethal configurations is astronomically low. The chances of two different organisms finding the same configuration from the same random space is even more astronomically low.
Some simple, easy-to-find examples:
- The marsupial wolf. Most wolves are placental. According to evolution, the placentals and marsupials branched away from each other 300 million years ago, in a small rodent-like animal. However, strangely, in two separate environments (with different "selective pressures", mind you) nature seemed to invent the wolf twice -- once as a placental and once as a marsupial. For a comparison of skulls between these two species, see this diagram. There are differences between the skulls, but they are no more numerous than would be for "evolutionary homologous" structures.
- In fact, the wolves are actually just one part of the marsupial/placental convergence. There are a number of placentals who have marsupial counterparts. These whole-body similarities are even bigger than the individual piecemeal evolutionary homologies. See here, here, and here.
- The electrical sense apparatus in the ghost knifefish and the African elephant snout fish are regarded as convergent evolution even though it is highly complex and unusual.
- Antifreeze Glycoproteins which help fish survive freezing temperatures seem to have evolved completely independently.
- This is a great paper on convergent evolution. Unfortunately, however, since evolutionists paint both non-evolutionary homologies and analogies with the same brush, this paper includes a long list of both types, and its up to you to sort out which is which.
Homology and Embryology and Genetics
In order to prevent simply restating the work of Jonathan Wells, I will refer this section to his excellent article, entitled Homology in Biology. The essence of the article is that even evolutionary homologies have non-homologous developmental pathways, and that even evolutionary homologies often have non-homologous genes controlling them.
What is the Creationist Position?
Creationists look at biology a different way than evolutionists. For evolutionists it's all just a giant accident, and biology is simply sorting out the "how" of how we got here. For creationists, however, we assume that there is a purpose behind our creation, and the job of biologists is to learn the purpose behind the creation. It is the question of George Washington Carver -- "God, why did you make the peanut?"
This is certainly much more useful in biology. The notion of "vestigal" organs (organs that are evolutionary left-overs or non-functionals) is particularly damaging to research, as it closes off inquiry. While a creation framework would be saying, "God, the function of these are elusive, why did you make them?" and then begin a process of investigation, the evolutionary framework says, "gee, these are vestigal, guess there's no function there." This is happening right now with pseudogenes and "junk DNA".
Why are there homologous structures? That's a very good question. I don't know the answer to that, but I think that searching for that answer is a better idea than saying the false premise that its just from ancestry (its false because convergent evolution shows that even if evolution is true, the premise of it just being from ancestry is certainly false).
It's obvious, however, that life was created with patterns. Anyone who has designed anything knows the power of design patterns. As a computer programmer, I create programs continually using design patterns, and while similar programs share many patterns, very dissimilar programs share many patterns as well. In fact, almost all programs, for any purpose and on any platform, share the initialize->process information in a loop->finalize pattern. If you look at the many homologies that lie both in and out of the normal classification hierarchy, it opens up the possibilities that many of life's designs are a combination of patterns arranged in unique ways. As someone who designs for a living, it makes perfect sense to me. On the other hand, I'm not a biologist, so what do I know?
Personally, I think a lot of biologists are aware of these problems, and just don't say anything because they're jobs would be at stake. That's evident from the Rick Sternberg fiasco, and the number of scientists who are signing on with some form of ID or Darwin criticism. They aren't all creationists, in fact many are theistic evolutionists (which true theistic evolution differs significantly from neo-Darwinian evolution).
Hunter exposed many of the theological assumptions behind the evolutionary interpretation of homology. Most of them, in order to prove evolution as trumping creation, have to result in "God wouldn't have designed it this way." Of course, that requires you to have specific, theological notions. However, since they are usually unstated, they are not open to criticism.