How Transitional Forms are Identified, Pt. 2

This is a continuation of a previous post called "How Transitional Forms are Identified, Pt. 1." There will be at least one more post in this series after this.

Since similarities are not capable of determining whether an organism is a transitional form, is there some other way a transitional form could be identified? In theory, it would be possible to identify transitional forms, if they were to exist at all, by cross-breeding tests. According to the theory of evolution, a new species will first arise as a variety of an existing species. When this variety becomes separated from the parent species and exposed to different selective pressures, the variety diverges enough from the parent species that the two no longer breed together in the wild. It would then be considered to be a different species, since the definition of a species is a group of organisms that interbreed and produce viable offspring in the wild. The creation of a new species in a manner similar to that described above is called a speciation event. While a new species may not be capable of interbreeding with its parent species in the wild, it may still be able to interbreed under domestic or artificial conditions. Thus, interbreeding would be able to reveal a common genetic heritage.

Something interesting to point out is that the previous description of speciation does not contradict creation science. In creation science, there is something called a kind. A kind refers to a group of organisms all of whose members can interbreed with one another. A kind is larger, and more encompassing than a species. Another way to think of a kind is a kind describes a large group of organisms that all have a common gene pool. Individual species in that kind contain limited portions of that gene pool. So speciation can occur as genes get shuffled around, exchanged, and limited to specific groups. Speciation in creation science does differ from speciation in the theory of evolution because in the theory of evolution, speciation events are not limited to an exchange or limiting of existing genes: speciation in evolution will also include (and indeed, requires) the addition of new genes.

Now let’s go back to our speciation event and take the idea further. Suppose a series of speciation events takes place, so that now, rather than having a single parent species and then one daughter species, there is the original parent species, its daughter species, a daughter species of the first daughter species (a granddaughter of the parent species), and so on. Continue this process long enough, and a daughter species may arise that is incapable of interbreeding with the parent species under any conditions. Even at this stage, cross-breeding would reveal a common genetic heritage. For example, let’s call the parent species P, the daughter species D1, the granddaughter species D2, and a great-granddaughter species D3. While species D3 may not be able to interbreed with species P, species D3 could interbreed with species D2. Species D2, in turn, would be able to cross-breed with species D1, and species D1 could cross-breed with species P. So there is still a chain of interbreeding possible, again showing a common genetic heritage.

This chain of interbreeding scenario is now inconsistent with creation science. One kind is not capable of interbreeding with any other kind. So the fact that species D3 is incapable of interbreeding with species P would be evidence that they belong to separate kinds. In addition, there would be no intermediary species (in this case, species D1 and D2) that would bridge the gap between species D3 and P. So the existence of a chain of cross-breeding species would be a genuine example of transitional species, and would be consistent with the theory of evolution and inconsistent with creation science.

Now we have a criterion for determining whether an organism is a transitional form or not: it must be part of an interbreeding chain, where it is able to interbreed with two other types of organisms but the two other types of organisms are not capable of interbreeding with each other. Now testing the idea that transitional forms exist is simply a matter of going out into the world and looking for examples of interbreeding chains.

A survey of the natural world would reveal, however, that there are no interbreeding chains. There are plenty of examples where different species are capable of interbreeding with each other, but these form distinct groups, not chains. For instance, it is well known that a male donkey and a female horse can interbreed to produce a mule. A horse can also interbreed with a zebra, creating a zorse. However, a zebra can interbreed with a donkey as well. So there is no chain of interbreeding present. Rather, interbreeding groups are present. First off, it should be noted that this is consistent with creation science: individual species are limited groups of a larger gene pool, the kind.

There is, however, an explanation for the absence of transitional forms given by the theory of evolution. The modern theory of evolution includes the idea of punctuated equilibrium. This idea says that species remain in equilibrium (they exist without change) for long periods of time. New species are created when that equilibrium is disrupted, usually by outside forces, causing a rapid isolation of populations and eventual creation of new species. Rapid here should not be taken as instantaneous, but rather over a span of hundreds of generations, which is a long time in evolutionary theory. So according to this model, equilibrium is the norm and it is occasionally punctuated by rapid periods of evolution. This would mean then that, at any given time in history, the likelihood of finding a species in the midst of evolving is rare: most of the time, you will just see things in equilibrium. Another explanation for the absence of transitional forms today is that species alive today may indeed be transitional forms, but since we do not see them evolving into new organisms, and since they are sufficiently distinct from their parent species, they are not recognized as transitional forms.

What is needed, then, to identify transitional forms is a record. In this case, the record that scientists look to is the fossil record. Species that are alive today may be sufficiently different from their closest living relatives, but the transitional forms, the steps taken during times of punctuated equilibrium, may have left remains as fossils. So now we turn to the fossil record.

There is an immediate problem with looking for transitional forms in the fossil record: the organisms in the fossil record are all dead. Remember, transitional forms can be positively identified by chains of interbreeding. However, it is impossible to determine interbreeding patterns with animals that can not breed because they are dead. The only thing that can be used as an identification of relatedness of dead organisms is to compare their physiology to that of living organisms. In other words, transitional forms in the fossil record can only be identified based on similarities with other organisms. But as was explained before, similarities of features can not be used to determine whether transitional forms exist versus whether transitional forms do not exist at all. So now we are facing the problem of physical similarities not being able to identify transitional forms all over again.