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The Theory of Evolution


Evolution functions on these basic premises:

  • There are a number of imperfect replicators on Earth competing for limited resources (food / land)
  • The environment that these imperfect replicators inhabit determine which replicators are
  • successful and which ones are not by means of reproductive success.
  • Child replicators inherit their parents' DNA, this includes all positive, negative, and neutral replication errors.
  • The combination of these factors (imperfect replicators + limited resources + heritability) is what is responsible for the diverse number of species on the planet.

In order for a scientific theory to be successful, it has to explain what's going on in nature better than any other theories. Below is a list of empirical evidence (things we observe happening/going on in nature) that need explanation:

Endogenous Retroviruses (ERVs) are vestiges of ancestral viral infection that have been incorporated into a host's genome. ERVs are identifiable due to the presence of sequences that code (or once coded) for viral proteins, including gag (structural proteins), pol (viral enzymes), and env (surface proteins), as well as telltale long terminal repeats.

In a typical viral infection, a virus invades a cell, inserting its genetic code into the host cell's DNA. The viral DNA then "hijacks" the cell, causing it to produce more copies of the virus until the host cell bursts and dies. However, occasionally the invading virus becomes disabled when something goes wrong (from the virus' point of view) during the "DNA insertion" phase, leaving a chunk of "dead" viral DNA code that remains in the surviving cell.

Now, if the infected cell is a germ-line cell (a gamete), and if the gamete survives the viral infection because something happened to disable the virus, and if the gamete happens to be selected to become part of the "next generation", and then if the the viral "dead code" becomes fixed in the population, then the dead viral code will eventually be passed along to descendent species. Note: the probability of each event described above is quite small; the probability of the whole sequence of events required to fix dead viral DNA code in the population is extremely small.

Now here's where it gets interesting. There are many ERV's common to humans and chimpanzees. That is, identical ERV's can be found at exactly the same "insertion locations" in human and chimpanzee genomes. Now, when a virus infects a cell, the insertion location is largely random. That is, the probability of a particular virus inserting itself in the exact same place in a cell's genome multiple times is vanishingly small. Thus the probability of there being all those shared ERV's between humans and chimpanzees is vanishingly small unless humans and chimpanzees descended from a common ancestor. The pattern of shared endogenous retroviruses amongst humans, chimpanzees, gorillas and other primates is entirely consistent with the pattern of common descent predicted by evolution.

Interestingly, ERVs make up approximately 8% of our genome, while functioning proteins (genes that actually express something, like the genes for eye color) are only made from about 1.5% of our genome. image courtesy of http://www.genomesize.com/gregorylab

How A Retrovirus Works

Retroviruses, unlike some other viruses, are RNA-based. In addition to two single strands of RNA that constitute its genome, a retroviral particle also carries several copies of reverse transcriptase. After invading a host cell, the reverse transcriptase is used in a process called reverse transcription to decode its RNA into DNA, which it then inserts into the host cell's chromosome. With the newly created viral DNA in place, the host cell's RNA polymerase is used to make more virus RNA, a template for both the RNA new particles will carry into other cells and for mRNA, which produces the viral proteins. The new copies of viral RNA and proteins are collected together into a new virus particle, and set free to infect other cells.

The above list is a list (not all-inclusive) of the things we find in nature that need a biological explanation. The Theory of Evolution is the scientific theory that attempts to explain why we find these things happening in nature - such as birds with teeth. Birds having genes for teeth is strong evidence that they had an ancestor that did have teeth (dinosaurs).

All birds have genes for teeth that are not "turned on", just like all humans have genes for tails that are not turned on (most of the time).

Then we have Creationism. Creationists are people who believe that, in this context, life on Earth was willed into existence by their god(s). Creationsim is anti-science right off the bat - they start with their conclusion and try to shoe-horn the Universe into their assumed conclusion, ignoring any evidence to the contrary:

One side's methodology is extremely biased, the other's is objective. Which is which?

Most Creationists function under the false axiom that if they "prove" the Theory of Evolution false, this means that Creationism is true. This is could be categorized under the logical fallacy of a False Dichotomy. Proving the ToE false in no way means that Creationism is true. In order for Creationism to be found true, Creationists would have to provide evidence of creation.

Once that happened, then the Creationist would have to provide evidence that their respective god(s) did indeed perform the creation event.

Below is an index (off site) of common Creationist claims initially compiled by Mark Isaak of Talk.Origins :