Charles Darwin was an English naturalist born February 12, 1809. Darwin was interested in how both man and plants came to be the way they are currently. After a great deal of research he wrote a book titled On the Origin of Species by Means of Natural Selection, which was published in 1859. Through this book, Darwin created the term “descent with modification”, or what we now call “evolution”. According to Simon, Reece, & Dickey, the process of natural selection is one in which “the environment “selects” only certain heritable traits from those already existing” (Simon, Reece, & Dickey, 2013).
This process is commonly called adaptation. It is through this process that many species survives generation from generation. Darwin came about this theory through two primary observations, those of “overproduction and competition” and “individual variation” (Simon, Reece, & Dickey, 2013). The observation of overproduction and competition showed Darwin that all species have the potential of reproducing an overabundance of offspring that the environment cannot hope to be able to support.
This overabundance of a life form causes a certain amount of competition among the life forms that are occupying said area. As a species, humans see individual variation on a daily basis. All one need do is to look at another human to see that no two people are exactly alike. Even identical twins are not exactly the same in that each one has unique fingerprints. This serves as support for Darwin’s observation of individual variation. These two observations led Darwin to the inevitable conclusion of “unequal reproductive success” (Simon, Reece, & Dickey, 2013).
Simon, Reece, & Dickey explain this unequal success as “those individuals with heritable traits best suited to the local environment are more likely to have the greatest reproductive success: They will survive and leave the greatest number of surviving, fertile offspring” (Simon, Reece, & Dickey, 2013). These theories were a vast change from the thoughts held prior to Darwin. Aristotle believed all species to be fixed in nature. According to Simon, Reece, & Dickey, Aristotle based his theory on the Judeo-Christian writings of the book of Genesis (Simon, Reece, & Dickey, 2013).
One of the first naturalists to claim that living things did, in fact, change through time was George Louis Leclerc, Comte de Buffon. Comte de Buffon believed that chance or even the environment possibly played a role in these changes. However, Buffon’s ideas were speculation and he actually hid his views in his publication, Histoire Naturelle, according to O’Neil (O’Neil, 2012). The discovery of fossils opened a new world in the field of evolution. However, the acceptance of the possibility of extinction was not immediate. In fact, extinctions were not accepted as scientific fact until the mid-1800’s.
This discovery and subsequent acceptance, allowed the comparison of existing creatures with those that ceased to exist long ago. The ability to compare and contrast these animals revealed a great number of similarities, but it also revealed a great number of differences. The first naturalist to publicly present his ideas regarding the reasons for these changes in the life forms was Jean-Baptiste de Lamarck. Simon, Reece, & Dickey report that “Lamarck explained evolution as the refinement of traits that equip organisms to perform successfully in their environments” (Simon, Reece, & Dickey, 2013).
Lamarck based his theory on the suggestion that evolution was based on the inheritance of acquired traits. That is to say, he felt that one generation acquired a trait and then passed that acquired trait onto the next generation (O’Neil, 2012). While an easy theory to disprove, it was a starting point for Darwin’s research and later publication of his theory. Simon, Reece, & Dickey lay out five types of evidence that are in favor of evolution. These types are: “fossils, biogeography, comparative anatomy, comparative embryology, and molecular biology” (Simon, Reece, & Dickey, 2013).
Fossils are a visible record of life, an indelible mark that evolution that has left on the planet. Researchers and students alike can get and idea of what the organism looked like previously. Also, the viewing the fossil record can be some indication of the number of years that have passed since the creation of the fossil based on the location in which it was found as well. According to Simon, Reece, & Dickey, a fossil record is “the ordered sequence of fossils as they appear in the rock layers, marking the passage of geologic time” (Simon, Reece, & Dickey, 2013).
The definition of biogeography is “the geographic distribution of species” (Simon, Reece, & Dickey, 2013). Biogeography was the original basis for the formation of Darwin’s theory that the organisms living today are descendants of other life forms. Darwin believed that the species that are located in certain places, like the blue-footed booby, are there because they have evolved from ancestors were in that area previously. He felt that this explained why these animals are not found in any other place in the world.
This is the same reasoning behind the theory regarding the great number marsupials in Australia. The current league of thought is that these creatures evolved in this manner due to their isolation from placental mammals located in other parts of the world. Comparative anatomy is the “comparison of body structures in different species” (Simon, Reece, & Dickey, 2013). Scientists believe that because humans, cats, bats, and whales have a skeletal structure that is similar in nature in regards to the forelimbs, there is possibly a common ancestry the four species.
Darwin’s theory of descent with modification was referring to this very same thought. In fact, even dolphins share this same skeletal structure. Perhaps, dolphins and whales at some point had a greater use for the phalange-like bones that are in their forelimbs and are centuries (eons? ) of non-use, they became webbed and turned into flippers. While these four species obviously do not use the forelimb for the same function, there is still an undeniable similarity among them. Comparative embryology compares the early stages of development of life between different life forms and species of animals.
At one point during development, all vertebrates, humans, apes, snakes, birds, and fish, all look alike. Once each species passes this stage though, they each start to take on the characteristics inherent to its own species. But one has to admit that it is uncanny that even for that split moment in time, it is very difficult to tell one from the other based solely on what the embryo looks like. Molecular biology has been, what many would claim, the biggest argument in favor of Darwin’s theory. An organism’s DNA contains all of its hereditary information.
If or when two species contain DNA sequences that are close matches or very similar, then one can make the claim that they must have had a “relatively recent common ancestor” (Simon, Reece, & Dickey, 2013). This is the idea on which paternity tests are based. The opposite is true as well. When there are a great deal of differences between the DNA sequences, then the probability of the two beings having a common ancestor are slim to none. Using molecular biology, scientists now have the ability to create new hypotheses attempting to pinpoint where the splits in the tree of life have happened.
Darwin believed that all life came from a common life source, even the earliest prokaryotic organisms. Molecular biology now has the ability to provide some limited information that has the ability to potentially support this idea, but there is no way of proving it at this time. For example, through molecular biology, science has discovered that all forms of life use DNA and RNA. Scientists have also found that the genetic code is more or less the same for all life forms. Darwin’s theory was definitely advanced for his time. The idea of all life evolving from a single source is one that is difficult to believe.
It is also one that we may or may not have the complete answer to some day. Certainly, it is a hot topic among both the evolutions and the creationists. The evolutions theory, in and of itself, is an enigma. There is a great deal of information that supports it, but who can say that there will ever be a thorough enough answer to satisfy all. It does not matter which side of the coin one favors, at the end of the day, we are faced with the fact that even in the last century or two, there has been enough changes in some animals that one cannot deny that there is some evolution at work.
