A Discussion on the ideas Charles Darwin presents in his book “On The Origin of Species” including evolution and natural selection along with the explanation to validate some of the problems he found with his own theories. Written for the Evolution course at Muhlenberg College on March 19, 2008.
Charles Darwin published On the Origin of Species in 1859 (vii), almost 150 years ago, in a time with out many of the modern conveniences we are used to, including the understanding of genetics. From this you would think that there was no way that he could have come up with some of the things we know today concerning inheritance of passing on genetic information to offspring. This is true, Darwin did not know about genes but he did know that information was passed on to offspring. He saw that over time this information changed and caused variation. He proposed that if these variations accumulated they would eventually form a new species, different from the one they started out as. Living in relatively similar environments, the two species would compete to get the necessities they each needed to live, with one species eventually going extinct because it was not as fit, this process being called natural selection. By looking at fossil records Darwin saw that as natural selection acted upon species that there was a flow of creatures, diversifying and changing over time, as a result of natural selection, which he called evolution. Some species went extinct and left no heirs. Darwin did have some problems that he could not solve because technology would not allow it but he did discover the mechanism of natural selection for the process of evolution.
Variation may at first be hard to understand but when you look at the human population there is much variation within our species. From our variation we could group ourselves, and if mating only occurred within that group, the trait that defined the group would become solid in the population, such as brown hair. After a long period of time other variations would also become very specific to that group, perhaps all having brown eyes, when the trait became desired in the population. If this selection of desired traits within a population continued and all other traits were excluded from mating into the population, this group may become a new species over time. This type of selection is called artificial selection which Darwin studied in pigeons. Pigeon fanciers, long ago, took rock pigeons and saw that a few pigeons had interesting variation and they mated those together so that the variation would become popular in the population. This occurred with many different traits and made lots of pigeons with crazy feather patterns, color variations, etcetera (20-29). These traits were selected for, by humans, not naturally, therefore we call it artificial selection. By seeing how it is possible to exaggerate variations in a population through artificial selection it is an easy jump to see how nature could produce a similar effect selecting through fitness, the ability to survive, the best species to live.
Natural selection acts on everything constantly. There is a famous Darwin quote which says “Nature is prodigal in variety, though niggard in innovation” (194). This means that there is lots of variation though this variation is not always positive, not leading to an innovation or evolved benefit. A species can only survive through natural selection by having a variation which make is advantageous over other species. A species, with an advantageous variation, will survive over a similar species lacking the variation, making the first species a dominant form. When this form not only out competes its relatives and other species in the same niche, it will the start to spread. It will be naturally selected for or against in other niches as it migrates and spreads over the world. The species will have to face competition of other species which have been selected for in other locations for the same niche. The best fit will then continue to spread. These species which spread greatly are called dominant forms as they will out compete many species in many different niches making them more adapt than other species. Through this movement natural selection has selected for the advantageous trait that species had. From this Darwin concluded that natural selection will never select for something that is detrimental to the species because this would cause it to not be dominant and would be out competed and disappear. Eventually part of this dominant species will gain a new variation which will be even more advantageous and will start to compete with its parent species forcing it to die back and the new variation of the species would become the new dominant form. This process is continually occurring for all species and is called evolution.
Evolution is a process which needs a lot of time to occur. Variations accumulate over time. These will not all be advantageous and some will have no affect at all and will not accumulate in a population. There are multiple processes through which species can evolve and change. Adults, for instance, are affected by the needs of their young. This allows for variations in young in affect the adult which will also gain variation though perhaps not in the same way. One important way that adult creatures can evolve is, if as young, there is a variation that alters perhaps a larval stage, this will alter the adult stage as well and may also be advantageous to the adult. This process is coined ‘correlation of growth’ (143). One thing that was important that proved evolution for Darwin was that he found the same types of species alive as he found in the upper layers of rock strata. This succession of types showed that the most recently dead animal would appear closest to the surface of the soil. It proved that the living species most likely came from their descendants which appeared to be dead, some having gone extinct (298).
Extinction actually leads to speciation. When a species starts to work best in more than one environment it may evolve to more than one species. The parent species will be competing with its closest relatives because they are most alike and both survive best in extremely similar environments. The new species then out competes’ parent species causing it to go extinct (302). All of the variations of the parent, living in slightly different environments, can become their own species different from their closest relatives (432). One of Darwin’s biggest points to prove evolution were the similarities of bone structures. There are many different species which have similar patterns in their leg bones such as whales, humans, and dogs. This shows that the organization of bones was very advantageous and evolved early on in animals. Being advantageous, the structures remained in the population while the rest of the animals continued to diversity and evolve while the bone structure remained the same though slightly altered for different purposes.
Above are a few examples of how Darwin saw evolution occurring, through competition of variations in the same species, as natural selection acted upon them. There were other things that natural selection acted upon to force evolution to occur within a population. Darwin believed in Lamarck’s view of use and disuse. This proposed that as a creature used part of their body more it would get larger in a sense or visa versa. For instance a giraffe would gain a longer neck because it used it more often to reach for leaves. It was then thought that this trait would be passed on to offspring after having been accumulated during the life of the giraffe. Darwin used this idea to explain why some cave animals do not have eyes or the ones they have are not useful. Darwin explained that over time they would use their eyes less and less and thus they would not be as efficient and slowly would disappear. Time is very important because Darwin thought that evolution needed a lot of time and a lot of generations to occur, mostly for variations to accumulate for natural selection to act upon (134-139). This idea of use and disuse was ingenious though it is not the real case as natural selection cannot act on something that is not there. The giraffe would need to start with a longer neck than another animal. This would require a random variation of a slightly longer neck which would be selected for by natural selection. Over time the variation would get more extended and would be continually selected for. In this way it was not purposely added to every generation but rather, by random chance, there was a variation which was a bit longer neck which was advantageous to the animal and therefore it survived and made offspring with the same variation and this then occurring repeatedly causing the evolution that Darwin saw. Darwin did believe that natural selection was the main mode of evolution though he did agree with Lamarck as use disuse being a second possibility which he had no way to prove or know it was not correct without knowing about genetics.
Today the topic of evolution is very controversial. Right after Darwin published his book On the Origin of Species evolution was widely accepted. Darwin had some amazing points to prove evolution and he even had a mechanism of natural selection. Some of his points were difficult to grasp and have now been found to be false though we still see how he thought about a lot of arguments against evolution and sought to prove those arguments were wrong. One of the most popular arguments is that of the complicated nature of many organism and their parts, particularly the eye of mammals would not possibly be able to evolve over time because it is so complicated (186-189). With the eye this is very untrue because what we see in nature shows that there are creatures with much simpler eyes, all of which are useful to the organism that uses the eyes. There are all levels of eyes that could be looked at to see how it could possibly evolve. The simplest are just light receptors which could only tell which direction the light was coming from. There are eyes slightly more complex which would have multiple light receptors and then more complicated were the ones that had multiple light receptors for different types of light. These are seen in the environment with worms having very simple light receptors and you can see the compound eyes of insects which can detect multiple forms of light with their simple light receptors. Our eyes could have come from these simplicities and many others, most similar to a combination of useful eye parts found in other creatures. The important of this is that it shows that the different parts of the eye could have been beneficial at different levels of complexity (186-194).
Darwin saw his major problem in the lack of intermediate species in the fossil record. This was nothing he could change, the fossils that would have proved evolution with no mistake had not yet been found and we are still searching for most of them still today. The real problem is that the fossil record is fundamentally flawed because of how difficult it is to make a fossil. It requires a creature to die and quickly be covered by sediments which would best occur in a shallow marine environment. Then it must not be disturbed for a very long time as great amounts of pressure are put upon the rock turning it into a single sedimentary stone. This may take millions of years to occur even with the right amount of heat and pressure put upon the rock. There also is the chance that the rock, once made, will erode and fossil layers will be lost (327). Layers which are older have a similar problem because the more pressure and heat given to the fossil may cause it to disappear all together (307). Even still not all creatures can be fossilized and usually only their bones fossilize. Therefore it is very unlikely that a creature will become a fossil to begin with then there is the problem of interpreting why certain creatures are found certain layers and not in others. A fossil can be found in a low layer, earlier in time, and then be missing in the next layer up and again seen in a more recent layer. It could be argued that this shows that a creature had gone extinct and then was recreated but this is false. As Darwin states creatures, once extinct, cannot reappear (313). This is due to the fact that it would require the species predecessor to evolve again though it is most likely that the predecessor went extinct when out competed by the recently extinct species. It is therefore more likely that the organism migrated during the time it was missing from the fossil record in the observed area and then returned to the area. This is very possible when you consider an ice age where animals most likely moved towards the equator and when it started to warm up again the animals would return to where they had lived before hand. Another possibility for sudden appearances of fossils is that a creature, once evolved, does need to first succeed before it can grow in numbers when it will be more likely to be made into a fossil with a larger population size. These problems all add up to creating the biggest problem when looking at the fossil record to prove evolution. First it is hard to make a fossil, second it is hard to tell where the fossil originated, and third not all fossils have yet been found. These all lead us to being unable to find all the steps in an evolutionary process of any creature. We are missing some variations and some species that did not dominate because this only existed in a small location. Migration patterns are also hidden we are then unable to see direct links in the same location. We then assume that a creature migrated when missing in the fossil record when it may just not have been fossilized for some time in that area. Since Darwin’s time we have found many intermediate fossils which help to prove Darwin’s point but we will probably never find all the intermediates between two species because many of them probably never became fossils (chapters 9 and 10).
Another big problem of Darwin’s was that he needed to explain how species migrated to other mountain tops, freshwater streams, and oceanic islands. As mentioned before, species could travel to other mountains during periods of glaciers when the colder climates covered areas of lower elevation. This would not only benefit the species because they would be able to spread but they also would not have to worry about the warm weather. It would not be likely that cold climate creatures would exist for a time in warmer environments because their migration will only occur as the species travels to an environment that will be most beneficial (365-373). Darwin suggested a similar process which would allow freshwater fish to migrate to other lakes and streams without having to live in salt water for periods of time. During times of high water and floods, fish could easily pass from one stream or lake to another, possibly over very long distances depending on the depth and severity of the flood waters (383-388). Concerning migration to oceanic islands, Darwin created a few experiments to test how animals would survive the travel. For plants it was simple, Darwin saw how both birds and fish could carry seeds in their digestive system for long periods of time and then the seeds would be deposited on an island. His experiments proved that even after passing through these digestive systems that the seeds would still be viable and grow on the island. A second experiment showed that over 300 plants could grow in a few tablespoons of soil. This soil could easily be brought to an island on the feet of birds bringing the plants with the bird (389-405).
Other species are more difficult to explain how they arrived on oceanic islands. Birds and bats could fly to the islands and then diversify there, creating more species, through evolution, after the creatures moved to the islands. There are some species such as large mammals and amphibians who are unlikely to ever arrive on oceanic islands This is because they have no way to get to the islands due to the distance for mammals and the salt atmosphere of the ocean for the amphibians (389-405). Darwin did a very good job at explaining these problems of migration though we can still look into the specifics of each situation to see exactly how each migration happened. This is because in different situations there may have been alternative methods even though these are very good explanations.
Darwin did have very good methods to explain his ideas on natural selection and evolution. There were some problems he saw like the fossil record, the complication of eyes, and migration, which could be detrimental to his theory of evolution. He did solve these well though there is defiantly still more research we can do to enhance his ideas. We can work to find more fossil intermediates though this still may not help because of the fossil record being fundamentally flawed. By looking at the fossil record we can also look to see if there is evidence of how our complicated eye evolved as well as looking at migration patters, which are usually hidden in the fossil record. These answers may never come about though this is defiantly an area which could use more research. Through this we will be even closer to explaining all the problems Darwin had in his research, mostly through our higher level of technology. In the end, evolution by natural selection was a great theory Darwin came up with that changed how we looked at the world and allowed science itself to evolve to where it is today.
Darwin, Charles. On the Origin of Species. Cambrideg, Massachusetts: Harvard UP, 1964.