Critical Thinking

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Biological Classification Many philosophical issues arise when considering biological classification and how species should be organized.  While there are different types of classification with unique qualities to each, there is often a debate on which biological classification system deems most effective.  The main purpose of the biological classification of species is to provide information on different species and how they all relate to one another.  The Linnean system, biological species concept, and phylogenetic systematics each bring different method of biological classification to the table which can be further analyzed to determine which method is most efficient. While classifying organisms into species may seem fairly simple, biologists cannot seem to agree on exactly what a species is.  In addition to not agreeing on what a species is, biologists also have hard time agreeing with how to classify, or identify, different species.  This disagreement between biologists is referred to often as “the species problem” (Okasha 97).  While it is obvious that not all organisms are alike, and that some organisms are more similar than others, biologists have a difficult time coming to a unanimous decision on how to classify these organisms and how to assign them to a particular species.  It is believed by Darwin that classification of species contains some degree of arbitrariness and that it is difficult to find differences in species, varieties, and sub-species.  While Darwin believed there was no real way to distinguish species from varieties and sub-species, Aristotle believed that there are ways to classify species “that are natural in the sense of corresponding to divisions that really exist in the world, rather than reflecting human interests” (Okasha 98).  Aristotle believed that there were natural divides within organisms and that species could be classified using those obvious differences.  For example, different types of cats look different from one another but you can tell when you are looking at a cat regardless of what type of cat it is.  And, you are able to confidently distinguish a cat from a dog solely by observation.  Using that natural divide you assume that all different types of cats fall under the same species and you know that a cat is considered to be in a different species from a dog.  While Darwin believed that determining if a group of individual organisms is a species is arbitrary, and Aristotle believed that there were natural ways of classifying species, German biologist Ernst Mayr believed that species could be classified based on their reproductive boundaries (Okasha 99).  Mayr concluded that if organisms are able to interbreed with one another, they are a part of the same species.  This theory became known as biological species concept, or BSC. Mayr’s biological species concept states that if two organisms are able to reproduce, then they must be a part of the same species.  One problem with this method of classification is that it only takes into consideration organisms who produce sexually.  Organisms, such as prokaryotes, that only produce asexually are not included within this method.  Another problem that arises when considering this method are hybrid zones.  Hybrid zones exist when species that are related live in two different areas where interbreeding doesn’t often take place between the two.  When considering the biological species concept these organisms could be mistaken for two different species due to their distant locations and the fact that they don’t breed or produce fertile offspring often.  Another problem that faces the biological species concept is the existence of ring species.  Ring species occur when various populations are dispersed in a geographical ring.  For example, populations 1, 2, 3, and 4 live geographically in that order.  1 can reproduce with 2, 2 can reproduce with 3, 3 can reproduce with 4, but 4 can’t reproduce with 1.  Due to the locations of these populations and evolution, Mayr’s concept would place populations 1 and 4 into different species classifications.   Another method of biological classification is the Linnean system, which was created by Carl Linnaeus and consists of classifying species through binomial Latin names, as do the other classification systems, but then organizing them into a series of “higher taxa” (Okasha 97).  An example of a binomial, Latin name would be Apis mellifera, which means honey bee (Binomial naming system).  In this method, species are placed into more broad forms of classification that include kingdoms, phylums, classes, orders, families, and genuses (Okasha 97).  This series of “higher taxa” is exclusive to the Linnean classification system.  Since the Linnean system was created when creationism was a prominent belief, the way species were classified into so many groups would make sense to most people of that time because they believed that God created every species separately (Okasha 100-101).Phylogenetic systematics, which was created by Willi Hennig, is the most recent practice of biological classification, developing in the 1960’s.  This method of classification states that classification of species should be “consistent” with evolution (Okasha 102).  The main point of this method was to pinpoint all of biological groups that are monophyletic which means they only contain descendants of a common ancestor.  Phylogenetic systematics’ goal is to “delimit higher taxa, rather than species” (Okasha 103).  This method makes an effort to make sure that organisms within a species are more related to one another than to an organism outside of their species.  I believe that the phylogenetic systematics biological classification method is the best way to organize species.  Mayr’s method seemed effective when I first started reading about it,  but once I realized how many problems there were with this method such as not including organisms who reproduce asexually, hybrid zones, and ring species, I realized that this would not be the best way to classify species.  I feel as if the Linnean system tries to classify organisms into too many categories in which many are uncertain and too intertwined with creationism to be biologically correct.  Phylogenetic systematics takes into account shared ancestry among organisms rather than just surface qualities and natural similarities.  Another reason that I believe phylogenetic systematics is the most effective way of classifying species is because the biological groupings are monophyletic which eliminates the creationism problem from the Linnean classification system.  In conclusion, phylogenetic systematics is the most efficient way of classifying biological species due to its ability to coincide with evolution and its focus on shared ancestry.