Transitional Fossils

Skeleton Cast of Struthiomimus altus. Getty/Stephen J Krasemann

Since Charles Darwin first came up with the Theory of Evolution and his idea of natural selection, evolution has been a controversial subject for many people. While supporters of the Theory point to the seemingly unending mountain of evidence for evolution, critics still deny that evolution is truly a fact. One of the most common arguments against evolution is that there are many gaps or "missing links" within the fossil record.

These missing links would be what scientists consider to be transitional fossils. Transitional fossils are remnants of an organism that came in between a known version of a species and the current species. Allegedly, transitional fossils would be evidence for evolution because it would show intermediate forms of a species and they changed and accumulated adaptations at a slow pace.

Unfortunately, since the fossil record is incomplete, there are many missing transitional fossils that could silence the critics of evolution. Without this evidence, opponents of the Theory claim that these transitional forms must not have existed and that means evolution is not correct. However, there are other ways to explain the absence of some of the transitional fossils.

One explanation is found in the way fossils are made. It is very rare that a dead organism becomes a fossil. First, the organism has to die in the right area. This area must have some sort of water with sediments like mud or clay, or the organism must be preserved in tar, amber, or ice. Then even if it is in the right location, it is not guaranteed it will become fossilized. Intense heat and pressure over very long periods of time is needed to encase the organism within a sedimentary rock that will eventually become the fossil. Also, only hard parts of the body like bones and teeth are conducive to surviving this process to become a fossil.

Even if a fossil of a transitional organism did happen to be made, that fossil may not survive geological changes on Earth over time. Rocks are constantly being broken, melted, and changed into different types of rocks in the rock cycle. This includes any sedimentary rocks that may have had fossils in them at one time.

Also, layers of rock are laid down over top of one another. The Law of Superposition asserts that the older layers of rock are on the bottom of the pile, while the newer or younger layers of sedimentary rock that are laid down by external forces like wind and rain are closer to the top. Considering some of the transitional fossils that have yet to be found are millions of years old, it could be that they just have yet to be found. The transitional fossils could be out there still, but scientists just have not dug down deep enough to get to them. These transitional fossils may also be found in an area that has not yet been explored and excavated. There is still a possibility that someone will yet discover these "missing links" as more of the Earth gets explored by paleontologists and archaeologists in the field.

Another possible explanation for a lack of transitional fossils would be one of the hypotheses as to how fast evolution happens. While Darwin asserted these adaptations and mutations happened and built up slowly in a process called gradualism, other scientists believe in the idea large changes that happened all at once suddenly, or punctuated equilibrium. If the correct pattern of evolution is punctuated equilibrium, then there would be no transitional organisms to leave transitional fossils. Therefore, the fabled "missing link" would not exist and this argument against evolution would no longer be valid.