General

The case for evolution

Evolution is a FACT, not a "theory". Scientists have different terminology from that used in everyday speech. In the scientific context theory does not mean a fuzzy hypothesis or a guess, but rather is defined as a framework which is made up of facts and is used to explain observations and make predictions. Evolution is ,for all intents and purposes, a fact simply because it has occurred and continues to occur. Darwin's theory of evolution is a scientific theory in the sense that it is a framework which consists of facts and is used to explain current observations or predict phenomena which may occur.

In order to offer a defense of evolution, I must define it. Many arguments posed against evolution are due to misunderstanding how it is defined by those who study it (Pigliucii). Strictly speaking, biological evolution is the gradual change in the genetics of a population over time. A simpler definition could also be the change of the frequency of alleles in a population from one generation to the next. When discussing biological evolution, scientists do not mean evolution of the universe, earth or individuals, but specifically evolution of populations of living organisms. Evolutionary biology does not attempt to find the origin of life, but rather limits its study to the evolution of populations of living organisms (Mayr). Scientists are discovering new clues frequently about the origins of the first life forms on earth, however regardless of how life on earth actually appeared, this says nothing against the fact that life has been evolving since (Rennie).

The evidence supporting evolution is overwhelming and comes from a wide variety of sciences including genetics, archaeology, anatomy, physiology, etc. Among the molecular evidence showing evolution are examples of redundant pseudo genes which show common descent. Pseudo genes are genes which serve no purpose and are not capable of transcribing into mRNA or being translated into proteins with a function. Redundant pseudo genes are genes which have counterparts which are functional in an organism (Theobald). Due to the fact that these pseudo genes serve no purpose and have no effect on the organism, mutations which occur in them would not be selected out by natural selection. It would make no difference what sort of mutation occurred in them because the genes themselves have no function. Basically this means that if the same exact redundant pseudo genes in the same exact chromosomes with the same exact mutations are found between two separate species or lineages of species then common ancestry is the only possibility (Theobald). There are numerous examples of the same pseudo genes being found between two separate species, one being the psi eta-globin pseudo gene, a beta globin gene which is shared among primates including humans and chimpanzees, suggesting a common ancestry among all primate species (Goodman).

Another example of molecular evidence in support of Evolution are endogenous retroviruses, which are simply genetic remnants of past viral infections. Simply put, endogenous retroviruses are viruses which infect organisms and then insert their genetics into the host's genetics which can thereby be passed onto the offspring of the host as part of their genome (Theobald). It is estimated that ERVs makeup about 5-8 percent of the human genome (Belshaw). If the same ERV sequences are found between two species or lineages then common ancestry would be the only viable explanation. Indeed there are several examples of common ERV sequences existing between humans and chimpanzees, implying a common ancestor of both humans and chimpanzees was infected with an ERV (Lebedev).

Another important piece of evidence for evolution is atavisms, the definition of atavism, though, makes it a bad word to start of using. Atavisms is basically mutations that shows pre-existing traits. These atavisms only make sense in the light of evolution, because they always adhere to the phylogeny of life. We see birds with teeth (M.P.Harris et al.), humans with tails (Mouied), horses with more toes (Tyson) and snakes with legs [1]. Which according to the evolutionary phylogeny, they all had once. But we never see mammals with feathers, fish with mammary glands or reptiles with fur. This is and can only be explained by the evolutionary theory of common descent.

As convincing as the genetic and molecular evidence and atavistic evidence supporting evolution is, more tangible evidence exists in the fossil record. The fossil record shows that life 50 million years ago was vastly different from life today. Countless species existing millions of years ago have gone extinct, and the fossil record shows that essentially no modern species existed at that time. The question then put forth is where all of the species living millions of years ago went, and from where did all of the species alive today come. The fossil record shows that the species of organisms living on earth have changed dramatically over the past few billion years. If evolution is indeed true, then there should be a clear transition between ancient organisms and their modern descendants. This fact is clearly observed in countless lineages and species where fossils of ancient species show transitions to modern species, suggesting that these fossils are ancestors of modern species.

Some critics argue that there are gaps in the fossil record. It is true that there are indeed huge gaps missing in the fossil record, and it is also true that scientists will never have even a small fraction of the total number of now extinct species documented. This reality is due to the fact that fossilization is quite rare.. While it is true that there are a lot of fossils, the number of fossils pales in comparison to the actual number of creatures that once lived. Any attempt to completely document the entire phylogenetic tree will be in vain; however, this does not mean that fairly complete lineages or aspects of the evolutionary tree cannot be known. This also does not mean that evolutionary trees cannot be produced on a small scale or that transitions cannot be shown between species. There are far more than enough fossils to conclude that evolutionary change has been occurring (Rennie).

While it may seem a stretch to conclude that simply because the bones of an ancient species show similarities to a modern species an evolutionary link necessarily exists, the process of determining whether a fossil is indeed an intermediate between two known species is much more detailed. When a fossil is found that is thought to be an ancestor of a later species, then based on this information predictions can be made about how an intermediate form between these two species may look, and these predictions often turn out to be accurate. One example is the transition between ancient reptiles and modern birds. A fine example is the archaeopteryx, a primitive bird living in the late Jurassic around 150 million years ago. There are dozens of other similar species showing transitional features between ancient reptiles and modern birds including the Confuciusornis, Microraptor, Sinosauropteryx and Caudipteryx .
As obvious as the facts supporting evolution are, it is not without its critics and skeptics, most of who come from religious circles who dispute evolution due to thinly veiled religious motivations. There are as many objections to evolution as there are areas of evidence supporting it; however, the one thing that essentially all of the objections have in common is the fact that they are based on misunderstandings of what evolution actually is, how it works or how science in general works. One of the oppositions to evolution, perhaps one of the most basic objections, is the argument that life today is far too complex to have evolved by random chance and must be the result of an intelligent designer, id is God. This objection may seem very difficult to address however once one understands the mechanisms behind evolution, it can easily be explained within the evolutionary framework. One popular analogy of the perceived highly improbable chances of evolution producing all of the diversity of life today is imagining all of the parts of a Boeing 747 laying in a junkyard. If a tornado comes through the junkyard, what are the odds of a fully functional jet airplane being assembled purely by chance due to the tornado? The answer is obvious, the chances of such a thing occurring are beyond astronomical, however this says nothing against the process of evolution.

The analogy of a tornado in a junkyard makes the mistake of assuming that evolutionary change occurs by chance, has a preset ideal in mind, and occurs in a single instance while none of which are true. Richard Dawkins, a British evolutionary biologist and science author, came up with an analogy which clarifies the mistakes that arguments such as the argument from complexity make. His analogy, called mount improbable, describes a very high mountain with an extremely steep cliff to the peak. If someone were to observe a mountaineer standing on the peak of the mountain, it would be incredibly hard to believe that the mountaineer got to the top of the mountain with one giant leap. In all likelihood the trip was taken gradually, step by step, up a much less steep side of the mountain opposed to leaping to the top in a single bound. This analogy clarifies the mistake that is made when assuming that modern complex structures of living organisms are too complex to have evolved. Modern structures did not appear randomly by pure chance in a single instance but are rather accumulations of millions of years of evolutionary natural selection built up upon each other.

Another type of argument which is based on the complexity of structures are arguments based on irreducible complexity. Michael J. Behe, a biochemist and critic of evolution, defines irreducible complexity as thus: "A single system which is composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning." The argument is that many structures in living organisms are irreducibly complex because if any aspect of those structures is removed then the structure would cease functioning and thus gradual evolutionary change is impossible because a structure must have all of the parts to function and any previous incarnations of the structure would be totally useless due to lacking certain required parts. This argument is incorrect because it requires that irreducible systems be incapable of occurring through evolution and also that some structures of living organisms are irreducibly complex, neither of which are true. If a system is indeed irreducibly complex then this does indeed mean that evolution by addition of single parts would be impossible; however, this does not disqualify evolution by deletion of parts, addition of multiple parts at once, or a change in function of at least one of the parts.

One example of irreducible complexity often given, indeed often given by Michael Behe himself, is that of the bacterial flagella. The bacterial flagella is a tail like organelle used to propel small, often single celled, organisms; an example being the tail of the spermatozoon of many plants and animals. The flagella consists of about 50 parts, which Behe argues could not have possibly evolved due to the fact that alone, none of the parts have any function and if any part is taken away from the flagella then it will lose its function and thus the flagella must have appeared in its complete form. Behe further argues that the chances of all of the parts of the flagella coming together in present to produce a fully functional system randomly are astronomical. This argument is incorrect in the fact that even when dozens of parts are removed from the bacterial flagella, the remaining system still has a function, specifically in the Type 3 Secretory Apparatus, which is basically an apparatus used by bacteria to inject protein toxins into the cells of their hosts. That even if numerous parts of the bacterial flagella are removed it can still function implies that it is indeed not an example of an irreducibly complex system. Other arguments from complexity put forth against evolution are claims that certain organs or systems in living creatures are simply too complex to have evolved or are otherwise irreducibly complex. One example often given is the human eye, which is claimed to be far too complex to have been the result of evolution and is irreducibly complex. Both premises of the argument are false in the fact that as previously described, systems do not form purely by chance in a single go but rather gradually evolve by natural selection which is opposite from chance. The second premise, that being that eyes are irreducibly complex is also false, this is a fact that most who have eye problems that are still capable of sight can testify to. There are also numerous examples of very simple systems at the lower levels of complexity such as basic photosensitive cells to much more powerful eyes such as those on the eagle which also show that eyes can range in complexity as well as functionality.

Sources:

Pigliucci, Massimo. "Evolution Alone Explains Life on Earth." At Issue: Creation Versus Evolution. Eric Braun. San Diego: Greenhaven press, 2005. Opposing Viewpoints Resource Center. Gale. 1June 2008.

Rennie, John. "15 Answers to Creationist Nonsense." Scientific American 287.1(July 2002): 78. Academic Search Complete. EBSCO. 02 Jun. 2008

Theobald, Douglas Ph.D. "Molecular Evidence - Redundant Pseudogenes" Talk.Origins Archive.12 Jan. 2004. Talk Origins. 02 Jun. 2008.

Belshaw, Robert and Vini Pereira. "Long-term reinfection of the human genome by endogenousretroviruses" Proceedings of the National Academy of Sciences. 101.14 (2004):4894-4899. 03 June 2008

Lebedev, Y. B. and Belonovitch. "Differences in HERV-K LTR insertions in orthologous loci of humans and great apes." Gene 247. 1-2 (Apr 2000):265-77.

Mayr, Ernst. What Evolution Is. New York: Basic Books, 2002.

http://en.wikipedia.org/wiki/Archaeopteryx

Goodman, M and BF Koop. "Molecular phylogeny of the family of apes and humans"

Matthew P. Harris, Sean M. Hasso, Mark W.J. Ferguson and John F. Fallon. "The Development of Archosaurian First-Generation Teeth in a Chicken Mutant"
Mouied Alashari M.D. Joy Torakawa M.D. "True Tail in a Newborn"

Tyson R, Graham JP, Colahan PT, Berry CR. "Skeletal atavism in a miniature horse"

[1] http://universe-review.ca/I10-10-snake.jpg