Muzaurieta 1

“ON THE ORIGIN OF SPECIES”

On the Origin of Species, published on 24 November 1859, is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology. Its full title was On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. For the sixth edition of 1872, the title was shortened to be justThe Origin of Species. Darwin’s book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. It presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution. Darwin included evidence that he had gathered on the Beagle expedition[1] in the 1830s and his subsequent findings from research, correspondence, and experimentation.

Various evolutionary ideas had already been proposed to explain new findings in biology. There was growing support for such ideas among dissident[2]anatomists and the general public, but during the first half of the 19th century the English scientific establishment was closely tied to the Church of England, and science was considered to be part of natural theology[3]. Ideas about the transmutation of species[4]were controversial as they conflicted with the beliefs that species were unchanging parts of a designed hierarchy and that humans were unique, unrelated to other animals. The political and theological implications were intensely debated, but transmutation was not accepted by the scientific mainstream.

Darwin’s book was written for non-specialist readers and attracted widespread interest upon its publication. As Darwin was an eminent scientist, his findings were taken seriously and the evidence he presented generated scientific, philosophical, and religious discussion. The debate over the book contributed to the campaign by T.H. Huxley and his fellow members of the X Club to secularize[5] science by promoting scientific naturalism[6]. Within two decades there was widespread scientific agreement that evolution, with a branching pattern of common descent, had occurred, but scientists were slow to give natural selection the significance that Darwin thought appropriate. During the “eclipse of Darwinism” from the 1880s to the 1930s, various other mechanisms of evolution were given more credit. With the development of the modern evolutionary synthesis in the 1930s and 1940s, Darwin’s concept of evolutionary adaptation through natural selection became central to modern evolutionary theory (MET), now the unifying concept of the life sciences.

Darwin pictured shortly before publication.

Summary of Darwin’s theory

Darwin’s theory of evolution is based on key facts and the inferences drawn from them, which biologist Ernst Mayrsummarized as follows:

  • Every species is fertile enough that, if all offspring survived to reproduce, the population would grow (fact).
  • Despite periodic fluctuations, populations remain roughly the same size (fact).
  • Resources such as food are limited and are relatively stable over time (fact).
  • A struggle for survival ensues (inference).
  • Individuals in a population vary significantly from one another (fact).
  • Much of this variation is inheritable (fact). This was a fairly new idea! This concept made Darwin’s next idea possible.
  • Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which produces the process of natural selection (inference). Modern students may take this for granted, but this is the core concept that Darwin added to the evolution debate that is really important. This was his theory about how evolution worked – and he was not saying that God guided all changes and made them happen.
  • The very slow process of natural selection results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference). This is the process we refer to when we say evolution. Scientific theory now accepts evolution to be true, even if every detail of the process is not explainable.

Work Cited

“On the Origin of Species.” Wikipedia: the free encyclopedia. Wikimedia Foundation, Inc., 23 September 2012. Web. 1 October 2012.

Note that the title is quoted, because that is the name of the article, AND italicized, because the whole article title is the name of a published book. This is an unusual situation. Usually, the article name will only be quoted.

I will freely admit that most of this is Wikipedia’s article, almost word for word, and they deserve all the credit. I did add some material to make ideas more clear, such as the footnotes, and italicized ideas at the end.

INFORMAL WRITING 2. People often argue over evolution. Some people think that natural theology and scientific naturalism are entirelycontradictory – that if one is true, the other is not. Other people feel that it is possible and rational to believe in both ideas. What do you think? Answer this question in a 10 minute timed writing. Use separate paper to write out your response. (Hint: you’ll need to consider the meaning of both “natural theology” and “scientific naturalism.”)

Additional reading for challenge option – students who want to do a bit more

Sparknotes:

Darwin’s theory is based on the notion of variation. It argues that the numerous traits and adaptations that differentiate species from each other also explain how species evolved over time and gradually diverged. Variations in organisms are apparent both within domesticated species and within species throughout the natural world. Variations in colors, structures, organs, and physical traits differentiate a multitude of species from one another. Heredity is the mechanism that perpetuates variations, Darwin argues, as traits are passed from parents to offspring. What is important about these variations to Darwin, though, is the way they allow species to adapt and survive in the natural world. He gives numerous examples of variations that illustrate the wondrous adaptations that allow species to survive in their natural environments: the beak that allows the woodpecker to gather insects, the wings that allow the bat to fly, the paddles that allow the porpoise to swim, and so on. Darwin hypothesizes that the minor variations we see within a single species—such as variations in size, shape, and color of organisms—are related to the more distinct variations seen across different species. His theory of evolution explains how variations cause the origin of species.

Natural selection is the key component of Darwin’s theory, as it explains the relationship between variation and the eventual evolution of a species. Borrowing from Thomas Malthus’s principle of exponential population growth, Darwin argues that the possibility of infinite growth of population sizes is checked by the limits of geography and natural resources, which will not allow an infinite number of beings to survive. As a result of limited food, water, shelter, and so on, species must engage in a “struggle for existence,” creating competition for survival. What decides, then, which species will survive and which will become extinct? Here is where “natural selection”comes in. Darwin argues that organisms exhibiting “advantageous variations”—variations that will allow them to adapt to their environment better than other organisms do—will be more likely to survive. Through heredity, these advantageous variations will be passed on to the organisms’ offspring. Eventually, natural selection will allow those species best adapted to their environments to survive and prosper, while species without these advantageous adaptations will lose the struggle for existence and become extinct.

Natural selection is the mechanism that leads to “descent with modification,” Darwin’s term for the process of evolution. Organisms will continually give birth to offspring that carry variations, some of which are advantageous and some of which are not. As advantageous variations are naturally selected and become perpetuated through successive generations, organisms carrying these advantageous variations will diverge from the original species, eventually becoming a species of their own. Continual modification and divergence, then, create a branching scheme of evolution, in which new species continually branch off from old ones. The “branches” help biologists link later species back to an original parent species, identifying the point at which different species are related to one another. Darwin notes that existing classification systems developed by naturalists already show these relationships between species. Darwin’s theory of descent with modification, then, simply provides an explanation for why many species seem so similar: Either they evolved from one another, or they both evolved from a common parent species.

After laying out the main principles of his theory in the early chapters of Origin of the Species, Darwin devotes much of the rest of the book to defending his theory against criticisms and presenting detailed examples of how natural selection occurs. The geological record is a formidable impediment to Darwin’s theory, as the existing fossil record does not provide the “missing links” in the chains of descent that Darwin proposes. In response, Darwin argues that the geological record is imperfect and that many fossil remains have been destroyed by changes in the earth or have yet to be discovered.

Darwin also attempts to explain how variations occur in species, driving natural selection and the creation of new species. Geographical isolation is a key component of Darwin’s theory. Darwin hypothesizes that because all species originated from one or a few original beings, species needed modes of transportation to migrate between geographical areas throughout the world. Barriers such as oceans and mountain ranges restrict the ability of organisms to migrate, and the few that manage to do so play a large role in shaping the evolution of species on islands and in geographically isolated areas. Geographical isolation accounts for the plethora of unique species on islands, as well as the wider distribution of species across continents.

Darwin’s theory challenged not only the prevailing view of the independent creation of species but also larger claims of religion and science. Darwin explicitly denied the validity of natural theology, which posited that species’ adaptations to their environments was proof of their “intelligent design” by a creator. It was natural selection, not independent creation, that resulted in these adaptations, Darwin argued. Moreover, Darwin’s use of scientific methodology to prove his theory amounted to an explicit critique of naturalists who would attempt to ignore the scientific validity of his theory because of its controversial nature. While the text of The Origin of Species did leave room for religious theology, Darwin’s overall commitment to scientific rationale rather than theological reasoning pitted him against religious doctrine. Darwin’s text was controversial when it was published, and it remains controversial today. However, his theory of natural selection has stood the test of time in scientific circles, and it remains the leading scientific explanation for the origin of species.

[1]Darwin traveled for years on the Beagle; one of the places he visited was the Galapagos Islands.

[2]A dissident challenges common and widely held beliefs; such people usually draw attention and criticism.

[3] Natural theology involves studying God by observing the natural world; notice this still assumes God to be evident everywhere.

[4] Transmutation is the idea that animals of one species could just turn into another species; this predated a modern understanding of how traits can be passed on genetically.

[5] Secular means not of religion. To secularize something is to separate it from religion.

[6] Scientific naturalism is the idea that the laws of nature do not in any way depend on magical or supernatural forces; that is, God does not create or rule the world in any way.