Evidence for Biological Evolution
The evidence presented here may be difficult for young learners. Please visit: http://amazinglife.bio/evolution/ for an easier-to-digest version of this presentation.
Understanding evolution is pivotal to the understanding of basic biological science. Without this understanding it is almost impossible to understand how new species come into being and behave the way they do.
Evolutionary theory is able to explain how species develop mechanisms to resist pesticides, how pathogens are able invade their hosts, how species adapt to differing environments, and answers many other perplexing questions about biological life. Evolution is also critical in discovering new methods to treat disease and predicting ways to help stop resistance to antibiotics. A common example of this resistance are super-germs being created from continuous use of anti-bacterial soaps. Evolutionary theory predicts that subsequent generations of germs could evolve into more dangerous organisms as a result of misuse of anti-bacterial products, but it also predicts that minimizing the use of anti-bacterial products will lessen the creation of these new super-germs (Levy, S. 2000).
Teaching students germ resistance to antibiotics is a common scientific example of the efficacy of evolutionary theory. However, our public schools continue to be a target for anti-evolutionists that wish to push alternate ideas about man and animal origins. Many of these alternate theories do not recognize the growing body of evidence in support of evolutionary theory. The evidence presented will hopefully provide a rebuttal to those that wish to undermine good biological science education.
All of the evidence for evolution is multitudinous and can in no way be listed in a single paper. However, the six strong evidences for evolution that follow should suffice to counter the many voices that doubt the veracity of evolutionary theory. The evidence that follows will consist of: Pseudogene Homology, The Vitamin C Broken Gene, Endogenous Retroviruses, Teeth Gene Expression, Missing Chromosomes, and The Phylogenetic Tree.
In trying to understand the evidence, it is imperative that there is an understanding of what genes are and their function. Genes are sections of DNA that are transcribed to perform a specific function. Making copies of themselves are part of their normal function. Alfred Sturtevant, a geneticist, was the first to discover these new duplications in 1925 while working with fruit flies. He discovered that some of the offspring had an extra copy of a gene (Sturtevant, 1925). Since Sturtevant, other scientists have observed new gene duplications in many different species, including humans (Fairbanks, 2007). These new duplications, or new copies, are imperfect; in fact, they are mutations of the original gene. Once a mutation occurs, genes rarely are able to perform the same original function. Continued mutations, however, allow this new gene to possibly perform different functions.
(Similarities in copied genes)
Finding the same gene duplications among homologous species lends some evidence for evolution (Fairbanks, 2007). These gene duplications are passed on from parent to offspring. A pseudogene is a copy of a gene.Humans and chimps share many pseudogenes. As pseudogenes are copies of genes, it is difficult to explain how the exact same pseudogenes could end up in different animal species; that is, without common descent. Evolutionary theory predicts that there should be very similar sections of genetic code among species that appear to be related, and there is.
Hemoglobin pseudogenes are some of the best understood pseudogenes. Hemoglobin pseudogenes are copies of working hemoglobin genes, which are responsible for transporting oxygen in the red blood cell. There are a number of hemoglobin genes that function at various times during human development. In many places in the DNA, there are inactive pseudogenes that sit right next to their parent hemoglobin genes. These groupings are called clusters. In the case of hemoglobin, these clusters are called the beta and alpha clusters. Within the beta cluster is a pseudogene of its parent hemoglobin gene, and it is filled with mutations. It is called the psi-beta pseudogene, and over 30% of its DNA has mutated compared to the parent hemoglobin gene (Chang & Slightom, 1984). All great apes have the exact same psi-beta pseudogene in the exact same place. New World monkeys, however, have the same psi-beta pseudogene, but lack an extra one that humans have. This reveals to us a deviation on a separate branch of evolution where somehow, after the great-ape split, New World monkeys lost their extra set (Chang & Slightom, 1984).
The Vitamin C Gene.
(The GULO UnitaryPseudogene)
A unitary pseudogene is a gene that has lost its ability to perform any tasks at all. A unitary pseudogene is the only one of its type found in the entire genome. This gene corresponds to what many of us have heard of as vestigial organs. For example, a mole in Australia known as the Marsupial mole has lost its ability to use its eyes. The gene that codes for connecting nerves from the eyes to the brain is gone; therefore, the mole is blind (Springer et al., 1997). It has no need for eyes at all, yet has them anyway as vestiges of its evolutionary past. If there is an identical pseudogene discovered in a separate mole species in the region, there is a good chance that these animals are related. They likely share a common ancestor.
Humans and the great apes share a unitary pseudogene of great interest in the scientific community and provides good evidence for evolution. A working example of pseudogene evolution is the gene sequence known as, L-gulonolactone oxidase. Commonly known as the GULO pseudogene or the GULOP gene in humans. The GULO gene is a gene that allows most mammals to create vitamin C on their own. However, humans and the other great apes, cannot create vitamin C on their own. This is because apes and humans have a broken GULO gene. At one point, the GULO gene allowed certain chemical products to be produced that allowed the synthesis of vitamin C, but it has now mutated to the point where it no longer serves the same purpose (Fairbanks, 2007). Not only do apes and humans share the same broken GULO gene, but the GULO pseudogene itself is also broken in the exact same place between humans and chimpanzees. The GULO gene is 98% identical and this is true of most of the genes shared between chimps and humans (Fairbanks, 2007)..
Some anti-evolutionists have asserted that the broken GULO gene is in fact not broken at all, that it serves some purpose within the genome and is therefore not sufficient evidence for evolution. However, even if true, they must explain why all apes are absolutely dependent on exogenous sources of vitamin C to live (Ha et al., 2004).
Compared to functioning GULO genes in non-primate species, the human GULO pseudogene has mutated over 20% the length of the gene (Fairbanks, 2007). Thus, with so many mutational accumulations along the gene, the earliest changes to the GULO gene in humans must have happened long ago. All apes have the same mutations. This means that their ancestor at one point passed down the broken gene to them. Humans, which are apes, have the same broken gene; which suggests that humans share a common ancestor with them.
Within our genes and pseudogenes are remnants of an invasion; a viral invasion that occurred to our ancestors long ago. Those ancient viruses invaded their germ(sex) cells, wrote themselves into the DNA and passed themselves on to the next generation. Due to the fact that no copy is ever perfect, when cells replicate, they produce errors. Provided that this mutation is not disastrous to the organism it has infected, the virus eventually becomes inactive and is passed on to future generations. These are called endogenous retroviruses (Wikipedia, 2009). They are fossils within our DNA.
Endogenous retroviruses, (ERVs) provide a very strong case for evolution (Nelson et al., 2003). Humans and chimpanzees share many ERVs. It is believed that human endogenous retroviruses come from ancient sources, as currently, there is no evidence of any recent invasions of the human genome (Fairbanks, 2007). If the only way one can have an ERV is from an ancestral past (Flockerzi et al., 2006), and chimps have those same markers, this lends some evidence that chimps and humans share a common ancestor (common great-grandparents). Apes and humans share many of the same ERVs, thus, it is very likely that they share a common ancestor that at one time contracted these viruses.
Humans and chimps reveal a common ancestry via endogenous retroviruses, but they are not the only organisms that do. Many small wildcats also share ERVs (Douglas, 2007). These cats, at one point in their evolution, shared a common ancestor that passed down remnants of their viral history to them.
The Missing Chromosome
It is widely accepted that humans and chimps share DNA; that is, they are cousins genetically. However, some anti-evolutionists do not accept that humans evolved from the same great ancestor. They use the chimp/human chromosomal “mismatch” as justification. Humans have 23 pairs of Chromosomes while chimps have 24 pairs. For decades it was not known, with certainty, why chimps had one more set of chromosomes than humans. The evidence is in on the strange chromosomal differentiation between chimps and humans. Human chromosome Number 2 has many representatives in Chimp DNA at their 2a and 2b sites (Avarello et al., 1992). This observation shows that that there is some kind of relationship between these three genes.
Figure 1.1: Source: (http://www.gate.net/~rwms/hum_ape_chrom.html)
A comparison of human chromosome 2 with chimp genes 2a and 2b.
A total deletion of a chromosome pair does not make sense in an evolutionary model. It was speculated that a well known biological process seen before in the genome of other animals may have occurred in humans. This process is called fusion. Fusion occurs when there is a head-to-head joining of chromosomes. Human chromosome Number 2, at one point, was two distinct chromosomes that somehow fused (Ijdo et al., 1991). The diagram above shows a visual relationship between all 3 chromosomes. The dark bands are repeating segments of DNA which have been stained. There are distinct homologies that should be readily apparent along the bands.
At the chemical level, the evidence is even more revealing. The nucleotides match up almost perfectly along the gene with a 98% similarity between them (Fairbanks, 2007). Thus, at one point, an ancestor related to chimps and humans had a fusion take place between his 2a and 2b chromosome which eventually led to our long-armed human chromosome 2. Chromosome 2 is also found in Neanderthal DNA, which correctly places man and Neanderthals as cousins that diverged from a common ancestor that possessed the fused gene.
Chickens with Teeth
A mutant chicken was discovered that possessed teeth much like a baby crocodile. It is a mutant chicken called a Talpid (Harris et al, 2007). Some anti-evolution advocates have argued for centuries that all organisms that are available to us today, were created as they are, complete and unchanged. Thus, with this presupposition, evolution cannot be true. However, Talpid chickens provide “naked-eye” evidence of evolution.
It is widely accepted within the scientific community that birds and reptiles share a common ancestor (Press, D. 2005). If this is true, bird ancestors at one time had teeth. The fact that Talpids have genes that express teeth is more evidence of evolution. Evolutionary theory predicts that there should be some evidence of reptilian ancestry via the DNA. The tools to discover this are now available. Scientists can now turn on the genes that express teeth in normal chickens and cause teeth to grow (Carey, 2006). This is significant in that genes can not express particular cellular morphologies unless the base code is already there, at least in part. Domestic chickens carry genes to grow teeth, but they are turned off (Carey, 2006). In other words, scientists did not create the teeth, the genes were already there. The machinery to create teeth in birds is already present; a remnant of their evolutionary past; thus, the machinery should not be there if bird ancestors never had teeth. To further explain via analogy, there are no genes for humans to grow wings for instance, as such, scientists cannot activate a wing gene as humans do not have any ancestors that possessed wings, therefore, the “wing-gene” does not exist.
The observation that organisms can express certain morphological characteristics from their ancestral past is nothing new. In the early 1900’s, Etienne Geoffroy Saint-Hillaire noticed tiny bumps along the beaks of parrots during the early stages of their development (Biello, 2006). It appears that all birds have similar machinery within their genome to express teeth. In the case of chickens, there is no doubt that they have a common ancestor that at one time had teeth.
A phylogenetic tree or evolutionary tree is a tree showing the evolutionary relationships among various biological species or other entities that are believed to have a common ancestor (Wikipedia, 2009). It used to be the case that this was performed by morphological comparison only, such as by observing external and internal characteristics of an organism. Looking at wolves and foxes, for instance, makes it pretty easy to place them on a tree as “cousins” due to their obvious morphological characteristics. Examining a cells’ organelles (tiny functioning interior parts) and also analyzing their chemical make-up, provide a very clear picture from which to deduce relatedness.
Once DNA could be analyzed and genetic sequences could be compared, a whole new avenue was available to scientists and taxonomists. It became possible now to look at gene sequences and compare them with other animals to see relationships. Scientists can analyze DNA samples of unknown origin, yet still produce a phylogenetic tree that overlays, uncannily, with known phylogenetic trees (Ogunseitan, 2004). Essentially, what this means is that a family tree can be produced using DNA only; showing cousin relationships. Evolutionary biologists no longer have to rely on homologies only. The DNA is sufficient to show relatedness. Now that we have DNA at our disposal, it is possible that a scientist can look at DNA samples of an unknown origin and still produce a phylogenetic tree (a family tree) that overlays almost perfectly with “known” phylogenetic trees. This overlapping is very strong evidence that evolutionary theory is correct.
There is good evidence for evolution. Opponents that have issue the most with evolution and evolutionary theory are those with limited knowledge of what the scientific evidence provides and/or are biased against the evidence due to other non-scientific convictions. Some anti-evolutionists, for instance, assert that humans were created in one day, are fundamentally different from other animals, and were made special. Modern genetics however paint a very different picture. In modern day evolutionary models, there is seen a rather steady rate of gene frequency change in species over long periods of time; humans included. The accumulation of pseudogenes align perfectly with the theory of evolution, but not so much with an instant and special creation concept. Evolution explains elegantly why species share pseudogenes. Alternate ideas about man’s origins fail to explain pseudogene placement among homologous organisms.
Just as importantly, evolution is an established fact within the scientific community. It is possible, that the sciences would not exist if we didn’t develop a system to know what is and what is not true about our world. Accepting evolution is a critical foundation that is required to understand the many aspects of life we see around us today.
The evidence reviewed provides sufficient evidence of common ancestry. Chimps and humans share identical pseudogenes and evolution explains how this is possible. Organisms that are the most similar share more DNA. Humans and Chimps have many of the same viral insertions that can only be passed down via sexual reproduction. Evolution provides a working model to make sense of the evidence provided. Evolution, descent with modification, is a well accepted theory that makes sense of what we see in the biological world. Based on the genetic evidence at hand, evolution from common ancestry is true. Humans are cousins with not just modern apes and primates, but all creatures on this planet. Every living being on the planet Earth, all share a common ancestor in the grand tree of life.
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* Article Originally Posted at ReginaldFinley.com. Edited for AmazingLife.Bio on 02/27/2016