Where Did We Come From? An Exploration of Different Theories of Evolution

This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

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Biology 103
2001 Third Web Report
On Serendip

Where Did We Come From? An Exploration of Different Theories of Evolution

Alexis Baird

Where did we come from? It is a question that has haunted the entire history of humanity. Thousands of years ago, our ancestors sought to answer the question with myths. Today, we are still struggling with the same question—only today we seek to answer this mystery with science.

Given various observations, it seems plausible that all life arose from a few very simple organisms millions of years ago. Observations of life will raise two important (though almost paradoxical) questions: Why are there so many different kinds of life? And why do there appear to be some over-riding similarities among organisms? The diversity of life is apparent in the vast number of different species of plants and animals that exist on earth. By the mid 20th Century, there was an estimated 1 to 2 million different types of organisms. (12) Now, however, the number is even higher and is expected to continue to climb as more discoveries are made. That there are prevailing similarities among organisms is equally apparent. (13) All organisms use the same biochemical mechanisms to function. For example, all organisms use DNA and many proteins that make up cells and serve as enzymes are the same across species. (12) Also, organisms that are supposed to be closely " related" tend to share certain characteristics. For example, the bones in a whale's front flipper are arranged in much the same way as the bones in human beings' arms and both whales and humans are mammals and therefore more closely related than say humans and squid. (12) Evolution - as defined as - the theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations" (20) can explain both of these phenomena. If all life on earth arose from one common ancestor it makes sense that they should have common characteristics. Once the theory of evolution is accepted, there is still disagreement as the how evolution occurred. This will be the focus of my paper.

Until quite recently, neo-Darwinism - as defined as the combination of Darwin's theory of evolution of the species through gradual change guided by natural selection coupled with modern genetics - was accepted as THE theory of evolution. However, lately neo-Darwinism has fallen out of favor. Since neo-Darwinism has always been the most widely Observations in nature would appear to support the claims of Neo-Darwinism. Just as Darwin hypothesized, organisms in nature do produce more offspring than can survive and reproduce given the constraints of the environment. (12) Richard Milton argues, however, that evolution does not arise from " survival of the fittest" , but rather " survival of the most prolific" . (13) This argument is valid to a point. However, if an organism has a characteristic that enables it to survive longer than its peers that organism will have time to breed more times and therefore have more offspring.

Neo-Darwinism rests on the theory that random genetic mutations over thousands of generations resulted in evolution. And there have been studies proving that genetic mutations could serve as the mechanism by which evolution occurs. A group of scientists in London discovered a way in which trichromatic vision could evolve from dichromatic vision through minor genetic mutations. The switch from trichromatic vision to dichromatic vision would entail the change of only one nucleotide pair (out of 80) which would alter an amino acid which would modify color sensitivity. (15) There have also been instances of genes mutating without losing their function as well instances (albeit fewer) where genes mutate enough to alter their function. (15) Also, the insertion or deletion of a nucleotide could cause whole genes to be turned on or off. (15) These discoveries imply that it's relatively easy for a small genetic mutation to alter an organism physically. Yet, they tend to be the exception to the rule. (15) In the case of the color sensitivity example, though the trichromatic vision arose fairly easily from dichromatic vision, the study fails to address how dichromatic vision arose. Somewhere along the line of evolution, dichromatic vision had to arise from no vision (in a relatively short period of time) and that's a considerably larger leap—a leap that perhaps Neo-Darwinism can't explain.

In recent years, the theory of Neo-Darwinism has fallen under attack for a variety of reasons. Writes Richard Milton, a scientist censored for his criticism of Neo-Darwinism: " …much of the empirical evidence that was formerly believed to support the Neo-Darwinism mechanism of chance mutation coupled with natural selection has melted away like snow on a spring morning…" (13)

It appears improbable that chance mutations of DNA could produce the complex organisms that exist on earth today. The human eye, for example, is so complex and efficient that no scientist would ever be able to create something comparable using technology. (14) Yet Neo-Darwinism relies on chance point mutations to create new organisms. Point mutations may allow for the activation of an existing gene, but not the creation of an entirely new gene. Brig Klyce, a critic of Neo-Darwinism, compares the theory that point mutations could give rise to completely new genes to " saying that a great work of literature such as ‘Moby Dick' could emerge from lesser pre-existing books if there were enough typos and swapping of paragraphs along the way." (15) A single nucleotide substitution may be able to alter a virus's protein coat such that the host's immune system won't recognize the virus, but point mutations cannot account for something as complex as say the development of photosynthesis. (15) The example of the moths that switch color over a few generations to adapt to their surroundings and the example of viruses developing resistance to previously effective antibiotics, are both actually instances of organisms not in fact developing completely new genes, but rather utilizing existing, " latent" genes already present in the genome. (15) However, the critics of Neo-Darwinism do not explain what causes these " latent" genes to be used (though maybe it's obvious to people with more scientific knowledge than myself). The use of these " latent" genes raises another interesting question that the critics of Neo-Darwinism neglect to answer: Where do the " latent" genes come from? If one assumes that evolution took place (though not necessarily Neo-Darwinian evolution), is one to also assume that the first cell possessed all possible genes?

Statistically, the life that exists on earth today is highly, highly, HIGHLY improbable. As mathematician David Belinski points out " from a mathematical point of view, Darwinian theories appear far too weak to have brought about the remarkable structures evident in living creatures." (17) If one assumes that all life arose out of random generations of proteins then there's a problem. First of all, every known example of genetic mutation either produces no noticeable change or causes death (or in rare cases undoes the mistake of a past mutation). (19) Yet, Darwinian evolution relies on random point mutations creating lots of biological advantages. The ratio of useful proteins to possible random proteins is 1:10500. (18) Therefore, barring incredible luck, it would take about 10500 trials to produce one useful protein when a cell needs a minimum of one to two thousand proteins. (18) Hence, life appeared on earth (and evolved) too quickly for the Darwinian theory of evolution to be completely correct.

The speed of the progression of species we see in the fossil record is not consistent with the amount of time it would take for the gradual evolution proposed by Neo-Darwinism. It is almost certain that genes have diverged over time creating new species. (15) However, how these genes diverged is the debatable point. Neo-Darwinism maintains that genetic divergence results from chance mutations, however, life has evolved much too quickly for this theory to be plausible. Take for example, Chimpanzees and humans whom are supposed to share 98% of their DNA. If one assumes organisms with a generation time of 20 years could accumulate about 1700 mutations (about accurate for both chimps and humans), then it would still not be sufficient enough to explain the genetic difference between chimps and humans. (14)Neo-Darwinism maintains that evolution is a gradual smooth process yet the evidence is to the contrary. There are numerous " gaps" in the line of evolution. For example, the evolution of horses—long thought to be a good example of neo-Darwinian evolution—has missing links. There is no link between Eohippus (a small dog-like animal that existed 50 million years ago) and its descendent Mesohippus (a sheep-sized animal that lived 30 million years ago). (13) No major changes occurred among the first life for about 2 billion years and then about 570 million years ago there appears to have been a general upsurge in evolution called the " Cambrian Explosion" in which a variety of multi-cellular organisms seemed to appear out of nowhere. (15) This " Cambrian Explosion" is inconsistent with Neo-Darwinism. Of course there does exist the possibility that for whatever reason, we've missed the links between ancient organisms and their descendents in the fossil record. Fossils (especially extremely old fossils) don't always survive for us to find them. There also exists the possibility that something occurred around the time of the Cambrian Explosion that caused an increase in chance mutations. There have been examples of fertilizers causing an increase in genetic change in tobacco and flax. (13) It would not, therefore, be too unreasonable to assume that there could exist something that would cause an acceleration in genetic mutation.

Several of the assumptions made by Neo-Darwinism are inaccurate. According to Neo-Darwinism, the closer two organisms are related (i.e. the later in time that they diverged), the closer their DNA should be and the more similarities they should have. Yet there can be greater variance in DNA between two species of frogs than between a bat and a blue whale. (13) I believe, however, (in my limited understanding of genetics) that this phenomenon is not quite so mystifying when one considers that not all DNA codes for a physical trait. The two species of frogs may share DNA that codes for physical characteristics, but not the other DNA in between the genes. This explanation doesn't exactly reconcile the evidence with Neo-Darwinism though (unless I'm missing something).

If Neo-Darwinism is correct, than one would expect to find that " simple" organisms have " simple" DNA because they didn't evolve. While this assumption may be true in some cases, it runs contrary to evidence in other cases. For example, goldfish have more than twice as many chromosomes as humans. (13) Yet, I don't think these observations necessarily disprove Neo-Darwinism. Neo-Darwinism does not state that evolving necessarily entails becoming more complex and gaining more DNA; it simply entails surviving to reproduce over other members of the same species. It would appear that complexity, quantity of DNA, and amount of evolvement are variables independent of each other.

My own personal criticism of neo-Darwinism rests on what I see as the inconsistency between slow, gradual evolution and relying on natural selection to direct evolution. Neo-Darwinism maintains that genetic changes and thus physical changes take place very, very gradually. If such changes are truly gradual and only take place over generations and generations, then how can such a small distinction make the difference between survival and death? In other words, according to neo-Darwinism, advantageous traits develop gradually, yet in the early stages of such traits, the distinction would not be pronounced enough to give the organism a noticeable advantage.

Since neo-Darwinism appears to have many flaws, other alternatives must be proposed. Not only has the scientific community suggested more theories, but the religious community has advanced their own theories as well.

The religious implications of Neo-Darwinism tend to color the evolution debate and add to its complexity. Tom Bethell writes, " If the Neo-Darwinian claim is true and all creatures great and small are here on earth as a result of a long chain of improbable accidents, then we have little reason to believe that God exists or that life has any meaning whatever." (16) Though his reaction seems dramatic, it is nonetheless indicative of many of the reactions towards Neo-Darwinism. Given this context, many of the critics of Neo-Darwinism (though definitely not all) have attacked the theory from a religious perspective.

Jonathan Sarfati, a creationist scientist, advances an alternative to Neo-Darwinism that he feels is consistent with his religious views and therefore more accurate. Sarfati proposes that God created several different kinds of organisms that then interbred to produce the vast variety of species seen today. " Thus each created kind may have been the ancestor of several present-day species." (14) Even ignoring the lack of fossil evidence for such a theory, there is little to no evidence of animals from vastly different species interbreeding today. Sarafati goes on to argue that his theory would explain the rapid change of species since the process of interbreeding among the animals on Noah's Ark would be faster than chance genetic mutations. (14) Yet this argument doesn't address any " evolution" that occurred prior to 4,500 years ago (the time of Noah's Ark). Due to the flaws in Sarafati's argument, I don't personally subscribe a " creationist" theory of evolution.

Another alternative to neo-Darwinism, is Brig Klyce's theory of strong panspermia. According to Klyce's theory of strong panspermia, " microorganisms from space provide the new genes necessary for sustained macroevolutionary progress on Earth" . (5) In strong panspermia, evolution does not rely on random point mutations, but rather on horizontal gene transfer. (3) Microorganisms (possibly bacteria) from space insert a gene into another organism. The new gene may give the organism the capacity to better adapt to its environment and thus evolve. Bacteria on Earth perform horizontal gene transfer in place of reproducing sexually. (6) Bacteria can sometimes carry out a type of horizontal gene transfer called conjugation which can occur between bacteria and eukaryotic cells in which long fragments of DNA are transferred. (6) There have even been cases where a virus will invade a cell and its genetic material will be incorporated into the host cell's genetic material and benefit the host cell. (6) Klyce believes this phenomenon took place between organisms on Earth and bacteria from a different planet, and resulted in macroevolution. (4)Klyce feels his theory of strong panspermia can answer the issues that neo-Darwinism fails to address. " Many eukaryotic genes…seem to come from nowhere," observes scientist W. Ford Doolitle. (5) According to Klyce, these genes didn't come from nowhere; they came from another planet. The discovery of some genes that appear older than they should be according to the fossil record, leads Kyce to the conclusion that these genes were brought by bacteria (that had probably started evolving much earlier) from another planet. (5) Klyce believes his theory of strong panspermia --since it relies on the replacement of entire genes rather than point mutations-- would match the actual pattern of evolution. (3) Strong panspermia also might be able to account for the sudden bursts of evolution. An influx of bacteria from outer space would cause a rapid replacement of different genes and cause widespread changes in organisms resulting in accelerated evolution.

Though Klyce's theory of strong panspermia makes sense in many respects, it should by no means be completely accepted. Virtually the only advocate of panspermia is Brig Klyce, which is suspicious in itself. Also, even though neo-Darwinism doesn't seem to conform to a mathematical model, one still can't discount the role chance might have played. Just because the odds are very, very low that random point mutations produced the organisms alive today does not mean that such a phenomenon should be completely discounted. Also, disproving neo-Darwinism does not necessarily prove strong panspermia. It's possible that there is another reason altogether for life's rapid appearance and evolution.

The main problem with the theory of strong panspermia, is that it still fails to address where life came from. If bacteria from another planet gave the genes necessary for evolution to organisms on Earth, then we're still left with the question: how did the alien bacteria develop the genes?

I would finally like to propose a couple theories of my own that while they aren't perfect, might come closer to explaining evolution. While I realize that it's highly improbable that our species developed new genes and thus evolved out of random point mutations, what if the random point mutations only served to turn whole genes on and off? Of course this would entail the original " parent life form" having all the necessary DNA for every possible organism. Yet, as with the moth and virus examples, certain species have been known to change their physical characteristics by turning already existing genes on and off. (15) At the same time, this theory would be unable to answer where then, the original " master" DNA of the ancient " parent life form" came from.

Another alternative/amendment to neo-Darwinism would be that evolution took place not from random point mutations, but rather from an explosion of genetic mutations caused by environmental factors at a certain time. Depending on the type, radiation can cause an increase in genetic mutation. (21) UV radiation can cause point mutations and ionizing radiation can cause large deletions and chromosomal rearrangements. (21) Ionizing radiation, although typically associated with man-made causes, can come from natural sources such as the sun, cosmic rays, and naturally occurring radioactive elements found in the earth's crust. (22) Also such factors as heat or lack of oxygen have been observed to increase mutation rates in cancer cells. (24) Wouldn't it be possible to generalize that such factors would produce mutations (possibly advantageous mutations) in regular cells as well? Wouldn't it also then be possible for there to be an explosion of natural radiation or other factors contributing to genetic mutation at some point(s) during the Earth's history that would increase mutation and thus speed evolution? One of the problems with this theory is that organisms have " repair systems" to undo the damage of mutations. (23) However, the repair systems in cells susceptible to cancer have been observed to fail and once the repair system of a cell fails the chances of mutation during cell division drop from 1:1,000,000 to 1:1,000. (24) Though this still makes mutation unlikely, it does increase the chances.

I believe that some sort of evolution most likely occurred. However, the mechanisms that brought about this evolution are probably not the random genetic mutations proposed by neo-Darwinists nor the inbreeding of the original species made by God. I don't know exactly how evolution occurred, but I am optimistic that further studies in the future will yield a more definitive answer.