Darwin didn’t believe that all species were independently created (which seemed to be the most commonly shared belief). Instead, he seemed to think that it seemed more plausible for species to evolve into one another over time, adapting specifically and instinctively to their environment. The one question that Darwin struggled with was how was it that species could evolve into another over the course of time? Darwin was baffled by the hypothesis of other scientists before him. These said that: people who bread animals found a huge amount of variation between the offspring of their crosses. They often would enhance their stock to get a desirable outcome. Through artificial selection breeders were able to multiply the different kinds and types of the species they bread. The second hypothesis was that wild animals face a huge struggle to survive. Those with characteristics best correlated with their environment, ultimately have the better chance for survival. Darwin called this process natural selection. This was different than artificial selection, which was what the breeders did. They choose characteristics to better their income, such as those that would enhance the animal’s appearance. Natural selection however was a survival technique (1).
Natural selection is incredible in that we do not see how it is done, but the results are miraculous and awing. It looks as though each species or type of animal has been specifically constructed with so much planning, and it is shocking that this is all a result of a simple process without any blueprints. It seems as though such an organism is well designed since it has attributes of such sensible purpose such as walking, swimming, hearing, seeing, reproducing, eating, or more generally promoting the survival and replication of itself and it’s genes. It should then be assumed that such a sensational organism has been designed by a master engineer and is the very best that they could have created. However, because an engineer usually works out purpose and structure of the object and usually reconstructs it several times to make it work to the best of its ability, we can consider that organisms may not have an engineer. We can actually conclude that through time, nature has adopted. Such is the theory of natural selection, in that organisms adapt and change to best fit their circumstances (4).
The beauty and improbability of living organisms is too massive to have come in to existence by mere chance. The question is how did they come into existence to begin with? I as I said before tend to co-inside with Darwin’s answer. Each change in the gradual evolutionary process was simple relative to its predecessor. However, the whole sequence of cumulative steps in the process is anything but chance, when you bear in mine the complex details of the end result when viewing the simplicity of the origin. The cumulative process is a direct result of nonrandom survival (4). Haven’t you ever just walked outside and wondered how there got to be this many beautiful and amazing things on this planet? How did trees form and how did their leaves begin to change colors in the autumn and fall off in the winter when it gets cold? How is it that birds are so smart that they know which way is south and all directly migrate there for the colder months of the year? There is no answer for this, a small amount of order came from chaos and no one mind concocted it.
Now I want to discuss the difference between cumulative selection and single-step selection. In single step selection each new attempt is a fresh start, meaning each time you try to create something and fail you wipe the slate clean and try again, with the first product completely forgotten. Cumulative selection is where each improvement or addition as small as it may be is used as a basis for later construction. Human evolution is cumulative. In fact, the evolution of our entire planet is cumulative. If the evolutionary process had relied on single-step selection we would not be here today, nothing would. Cumulative selection is our explanation of all the wonderful things on this planet, how could all the beauty and co-existence be here right now if the process wasn’t cumulative? It simply could not. Chance plays a very minor role in Darwin’s evolution theory; the most important role is played by the nonrandom component of cumulative selection (4).
Now we shall go on to discuss the topic of inheritance. Over 125 years ago in Darwin’s time, everybody believed that inheritance was blending. However, a Scottish engineer by the name of Fleeming Jenkin decided that the fact of blending inheritance completely ruled out natural selection as a theory of evolution. Jenkin’s argument was about swamping. He said that as generations go by, under the assumption that inheritance is blended then variation is someday bound to become swamped. Eventually no variation will be left for natural selection to work upon and greater uniformity will occur. This argument may have sounded somewhat valid but in truth it is an argument not just against natural selection but also against heredity. It just isn’t true that variation diminishes as time goes by. People are no more similar today then they were in the time of our ancestors. Variation has always been maintained.
It is often thought that the theory of natural selection is purely negative. The whole idea of weeding out the failures and the incapability of building up efficiency and complexity of the design makes it look negative. You must look at evolution as an equation. If natural selection subtracts then mutation can add. Together mutation and natural selection can dominate over geological time to build a complexity that is far more positive than negative. This build up can happen in two different ways. The fist is called ‘co adapted genotypes’ and the second is called ‘arms races’. They are both very different but unite at the same time.
First we will talk about the concept of ‘co adapted genotypes’. This is the theory that a gene only holds the capacity that it does because it already works on an existing structure. An example of this is if there weren’t a brain then a gene couldn’t affect it’s wiring to begin with. The effects that genes have are not direct processes of the genes themselves. They are part of the existing process whose details are altered by the genes but not created. The entire process of embryonic development is a cooperative process and thousands of genes run it together. In the process of natural selection each gene is selected for it’s individual potential to flourish and meet the needs of it’s function within its environment. While we usually consider the environment the world around us around us, that of climate and predators, genes may not. For a gene the most important part of its environment is another gene and they are all functioning in the cells of the individual bodies of an organism. So natural selection occurs at the very depths of an organism as well. Each gene is purposely selected for it’s potential to successfully cooperate with other genes that they may come across in bodies (4).
Now we will discuss the second theme in natural selection, ‘arms races’. Arms races occur between predators and prey and parasites and hosts. While ‘co adapted genotypes’ are run on a timescale of individual lifetime, arms races are run on a timescale on evolutionary time. There are arms races whenever and individual has enemies with the same capacity as they do for evolutionary advancement. Arms races consist of the improvement in one lineage’s equipment to survive, as a direct result of an improvement in an opponent’s evolving lineage. Arms races can be held accountable for much of the progressiveness that there is in evolution. Nothing in evolution is inherently progressive. Animals adapt characteristics to survive in their surroundings. Hence why in dry places, animals come to have leathery or waterproof skin to conserve the little water source. Or in cold places they have thick coats of fur or hair to shield them from the harsh climate. These adaptations to certain surrounding conditions, affect every characteristic of an animal from their outside appearance down to the construction of it’s cells (4).
If the characteristics of an animal’s environment remain constant then evolution in that lineage may stop. For example if the habitat that an animal lives in remains dry and hot for 100 years without fail then the lineage for adaptations to climate will automatically halt. The animals become as well fitted as possible to their living conditions. Evolution comes to a plateau until conditions change again. Such severe changes such as an ice age or severe change in the humidity of an area can for a period of time could onset an animal to evolve again. These changes happen because we are dealing with a timescale so long. Evolution does not normally come to a halt, but constantly monitors the ever-changing environment. If a change persists over centuries then the evolution of an animal will change to better suit the long-term environmental shifts. The weather is extremely important to the evolution of both animals as well as plants. Patterns of climate change as centuries pass so evolution is constantly in motion and changing all the time (4).
The climate is not the only aspect of an animal’s environment that is constantly tracked. The concept of predator and prey is just as essential to the survival of a species. Cumulative selection allows animals to be able to out run their predators or outwit their prey just as it sees to it that they are well equipped to deal with the climate. Long- term changes in the habits of predators are monitored by evolutionary changes in their prey and likewise. There is a difference however in the change of weather over centuries and the change of enemy tactics over centuries. While changes in the weather are hostile they have no tendency to get steadily worse. Living animals, looking at the evolutionary time scale, seem to get much more hostile as time goes by. When two opposing sides improve their weaponry in response to the other; that is an arms race. Each new genetic improvement selected on one side, changes the environment for the other. It is arms races of this sort that are chiefly responsible for the progressive component of evolution. These arms races are not eternal but stabilize when farther improvements become either too costly to the individual animals (4).
After discussing Darwin’s ideas for the majority of this paper, I now want to discuss the newer information found about the molecular basis of life. The theory of evolution tells us that each living thing should have detailed molecular evidence of its relative place in the hierarchy of all living organisms. Such evidence is found in the DNA sequences of living organisms. A cell must copy it’s DNA before it can divide and produce offspring. When cells copy their DNA nucleotides they always make a number of mistakes. Because of this, several nucleotides are changed through a random error every time that a cell divides. So the larger number of cell divisions that elapsed between the time that the two organisms deviated from their shared ancestor then the more differences there will be in their genetic makeup due to chance errors. This molecular divergence allows researchers to track the different events of evolution using the DNA of different organisms. An example of this is the lineage that led to humans and to chimpanzees. Such information was found diverged around 5 million years ago showing to track the lineage of mice and humans you would need to look back much further, probably about 80 million years. As a result the difference between human and chimpanzee DNA deviates much less from that of mice and human. Scientists often use the differences found in the DNA sequences of organisms to determine the relationships between living things.
The same evidence can be found when measuring the proteins encoded by DNA. Every living cell utilizes a protein called cytochrome c in its metabolism. When measuring the cytochrome c in humans and chimpanzees you will find it to be identical to one another. However if you were to compare a human’s cytochrome c with that of a chicken, you would not find it to be similar at all. This is explained the same as the above belief that we shared a common ancestor with chimpanzees somewhat recently. In recent years, new methods have arisen that are allowing us to obtain the exact sequence of all the DNA nucleotides in chromosomes. Soon we will be able to obtain the entire sequence composed of 3 billion nucleotides that compose our genetic inheritance. Similar innovations in science will allow us to understand the complete sequences for hundreds of bacteria and other organisms (1).
These molecular studies give us powerful evidence regarding human evolution. It is baffling how when we know the exact order of the genes in our chromosomes we will be able to predict the order on monkey or even rodent chromosomes. The mammalian species is so similar that long stretches of the chromosomes in different mammals can determine the order on one another. Even the parts of our DNA that have no known function can be compared to DNA in similar organisms.
Darwin’s ideas about ‘decent with modification’ have been confirmed with this new molecular evidence. This has been one of the most astounding findings in the history of science. If more and more chromosomes can be sequenced over the next few years, then many of the missing pieces of our evolution and life on earth will be filled. This theory of evolution is now a generally accepted fact in science. While there is so much evidence to back up this theory of evolution, it is still one of most active fields in science. Discoveries are constantly being made to increase our understanding of living organisms (1). Just as the world has evolved and continues to, so does our understanding of evolution and creation and will at my prediction continue to for years and years to come.
References
- Bower, B. Gene fossil data back diverse human roots. Science News. 13 January 2001.
- Dawkins, Richard. The Blind Watchmaker. 1996 WW Norton & Company, New York.
- Kerr, Richard A. Evolutionary pulse found but complexity as well. Science. 28 September 2001.
- Second thoughts on man’s African origin. Business Week. 29 January 2001.
- UTD web pages on Charles Darwin
