To explain why transitional fossils are NOT found, Niles Eldredge and Stephen Jay Gould (1972) came up with the "punctuated equilibria" model of evolution, which is unique. It must be the only theory put forth in the history of science which claims to be scientific, but then explains why evidence for it cannot be found.

Addendum:

There are three topics that need to be covered when responding to this paragraph:

1. What a transitional fossil is,
2. What the theory of "Punctuated Equilibrium" is, and
3. What the evidence for "Punctuated Equilibrum" is.

TRANSITIONAL FOSSILS

What is a transitional fossil? A transitional fossil is the fossil of a transitional form.

A transitional form as traditionally used meant an animal halfway between two "classes" or "kinds" of animals. Archaeopteryx was often cited as an example of an intermediate form between "reptile" and "bird." As discussed on earlier pages, this view of evolution has been supplanted and its related taxonomy no longer used. Archaeopteryx is not a transitional between "reptile" and "bird." It is both reptile and bird.

As with many old terms, "transitional form" is still used, but with a different meaning (this is unfortunate in my opinion as most people are not aware of the shift in evolutionary theory and taxonomy, and continued use of old terms with new meanings causes confusion). The new definition of a transitional form, also called an intermediate form, is a species of animal that is intermediate between two different species of animal.

An intermediate form (IMF) is a species between any two species of animals, all in the same lineage. This IMF can be between a species that came immediately before the IMF (i.e. is the "parent species" of the IMF) and a species that came immediately after the IMF (i.e. is the "child species" of the IMF). I call this "fine-grained progression." An IMF can also be a species in between two more widely spaced species of animal. For example, a species can be an IMF between its "great-great-great-great-grandfather species" and its "great-great-great-great-granddaughter species" (the pictures on page 8 are great example of this). I call this "coarse-grained progression."

Anti-evolutionists/creationists latch on to "fine-grained progression" to further their arguments against evolution. The reason for this is the fact that the fossil record rarely preserves "fine-grained progression." It typically preserves instead the "course-grained progression." By ignoring "coarse-grained progression," they can claim there are no transitional fossils (of any definition) at all.

Anti-evolutionists/creationists also deny the existence of intermediate forms by pointing out that most species that are good candidates as intermediates between two other species often appear alongside those species. They claim that evolution requires that parent and daughter species cannot live with each other; one must displace the other, and since it did not, it is not a transitional form. As shown on page 3, this is a false argument.

Anti-evolutionists/creationists practically jump with glee when a supposed ancestor species is found in the fossil record after its supposed daughter species. Again, as shown on page 3, isolation can result in a daughter species that lives alongside, in time, its ancestor species, or an ancestor species that actually outlives its daughter species. If the ancestor species is isolated in an area where fossilization does not occur, while the daughter species lives in one where fossilization does occur, the daughter species would appear in the fossil record before its ancestor species, if the ancestor species ever appeared at all. Put another way, the fossil record shows only when that specific animal lived and died, NOT when that particular species evolved. The existence of an ancestor species later in the fossil record than a daughter species simply means that the lineage extends farther back in time than shown by the fossil record.

"PUNCTUATED EQUILIBRIUM"

Mr. Poling:

I don't pretend to know all the specifics of "punctuated equilibrium." As I understand it, it states that animals remain in a static state until environment pressure causes evolution. Evolution then occurs quickly. The more extreme the environmental pressure, the more extreme and the quicker the changes.

Studies of extant animals show that this is indeed the case. One example is the Galapagos Finches. In the early 70s there were two morphs of one species of finch on one island: a large beaked morph and a small beaked morph. A severe drought in the mid 70s brought about conditions that favored the large beaked morph. Within a generation or two, nearly all the finches were of the large beaked type and the small beaked were on their way out. Then there was another drought, one that created conditions that favored the small beaked morph. Within a generation or two nearly all the finches were of the small beaked type and the large beaked were on their way out. By the early 80s conditions had returned to normal, and now the population of finches is shifting toward a hybrid morph, with a beak intermediate between large and small. So within a DECADE you have two shifts in the morphs of a single species of finch extant on the island (natural selection), and the appearance of a third (adaptation).

Based on these changes, if the environment caused the right kind of pressure, an entirely new species of finches might appear in a relatively short period of time. Wallabies that were imported to Hawaii after the settlement of Australia can no longer interbreed with Australian Wallabies. North American fire ants can no longer interbreed with the populations of fire ants in South American from which they came. Interbreeding is fundamental to determining whether different populations of similar animals are of the same species. We have two examples of animals, in the course of a hundred years or so evolving new species or sub-species.

These studies suggest that the early hypothesis that species change slowly over millions of years were *wrong*. What these extant species show is that there are little or no changes in the species until environmental pressure requires it, and then evolution happens QUICKLY. Genetic changes can take as little as a century or two, and physical adaptation can take place in the matter of a DECADE or two.

Would fossilization catch changes that happen in the course of several hundred years? The geologic record has huge gaps in it measured in the THOUSANDS of years. The fossil record is therefore going to have similar gaps. With gaps thousands of years long in the fossil record and evolution occurring over hundreds of years, it is not surprising at all that organisms appear "fully formed" in the fossil record.

(To make the odds of finding "transitional" forms even worse is the rarity of fossils in the first place. Fossilization requires very specific and very rare conditions. For a carcass to be fossilized it must be quickly covered up by soil that is not too moist or too dry and not too acidic. Since fossilization requires the carcass to be covered up, only those animals that die in or are moved to areas of soil or sand deposition become fossilized. That means there's going to be a huge bias in the fossil record towards low-land or desert animals, where these conditions occur. Animals that lived and/or evolved in upland or arboreal habitats are unlikely to be fossilized, leaving huge gaps in the fossil record. Dr. Bonnie Blackwell of Queens College, New York, estimates that only 0.0000001% (1 in a billion) to 0.0001% (1 in a million) of all bones actually become fossilized.)

If evolution happens only during periods of extreme environmental stress, one would expect to see these "fully formed" new species appearing in sediments that showed vast environmental changes over the environment preserved in the next older layer. Does the fossil record show this? Indeed it does. For example, periods of large speciation occurred at the same time the Mesozoic inland sea of North America either grew or shrank. Occurrences of these types ... sea growth shrinking or obliterating habitats and sea shrinkage opening vast new habitats ... cause extreme environmental pressure.

Addendum:

The fossil record and careful examinations of extant species indicate that both the "gradualist" and "Punctuated Equilibrium" models are at play in shaping the animal world. Many species have changed only slightly over millions of years. Sharks are a good example of this. They are very similar to the first sharks that evolved millions of years ago, and their fossil record is a testament to their gradual change to their modern forms. But the fossil records of most species show rapid changes in their forms.

That evolution should happen over a very short period of time should not be surprising to anybody who really thinks about it. Evidence that ecosystems can change virtually in the blink of an eye abounds in the world today. For example, entire forests of a single genus of trees on the eastern coast of the United States disappeared when a deadly fungus appeared early in the century. If evolution truly occurred slowly, with only slight changes over millions of years, animals would never be able to adapt to such rapidly changing environments.

An excellent question would be "How do animals adapt to changes in their environment?" All animals have variations within their species. Just look at humans: there are short humans and tall humans, blonde humans and brunette humans, light skinned humans and dark skinned humans, hairy humans and unhairy humans. Often, some variation in the population will be better suited to a specific environment. If the environment shifts in that direction, it will give animals of that variation an advantage. Soon, most of the surviving animals carry the favored variation. This is called "natural selection." If no animal carries a favorable variation, the stress placed on the animals by the new environmental conditions can interfere with the reproductive process, creating mutations. If these mutations do not provide the animal an advantage in the new environment, or don't happen at all, the species will go extinct.

EVIDENCE FOR "PUNCTUATED EQUILIBRIUM"

Mr. Buckna states

It ["Punctuated Equilibrium"] must be the only theory put forth in the history of science which claims to be scientific, but then explains why evidence for it cannot be found.

This is either a misstatement, or Mr. Buckna is not familiar with science and with what "Punctuated Equilibrium" is all about.

Black Holes have been theorized about for many years. Many theories exist about the nature of Black Holes, where they occur, and why they occur. However, no Black Holes have been detected, with any certainty, from Earth. Many theories about why Black Holes cannot be found by terrestrial observation have arisen. Therefore, the statement that "Punctuated Equilibrium" is "...the only theory...which...explains why evidence for it cannot be found" is false. It is worthwhile to note that the Hubble Space Telescope has provided scientists with images that they believe are Black Holes. These images not only confirm their theories about the existence and nature of Black Holes, but they also have confirmed the theories of why Black Holes could not previously be found.

Regardless, "Punctuated Equilibrium" not only does not explain why evidence for it cannot be found, it does not even suggest that evidence for it cannot be found in the first place. Indeed, the entire fossil record, with species appearing abruptly, "fully formed", as predicted by the theory, is strong supporting evidence for "Punctuated Equilibrium."

Simply put, "Punctuated Equilibrium" is an explanation of why the fossil record is one of "course-grained progression."