Evolution in Everyday Life In its simplest interpretation, the term evolution means changing gene frequencies through time. Whether or not you believe that humans evolved from primates, understanding the concepts of evolution and its significance to our everyday lives is essential. All organisms evolve, and this can happen in more ways than one. Humans have purposefully and accidentally caused organisms to evolve through a variety of mechanisms including artificial selection. Artificial selection is the process whereby desired traits are encouraged and ultimately enhanced through generations of selective breeding by humans. Perhaps the best example of artificial selection is through the large ears of corn that we know and love today. Corn is used today for everything from livestock feed to human food to a sugar substitute in processed foods. Most people do not realize that corn started out as a completely different species known as teosinte, which looked and tasted much different than today s varieties (Kingsley, 2005, University of Utah 2012). Figure 1. Teosinte corn. Teosinte, which still exists today, is a bushier plant with a hard outer shell casing over a much smaller number of individual seeds. Initially, most of the plant s resources seemed to have gone into the vegetative portion of the plant rather than the reproductive stalk (Figure 1). These seed casings are thought to have been a protective covering for the seed to help it last through the digestive tract of animals that ate and ultimately spread the seeds. Page 1 of 6
Through generations of controlled crosses, believed to have been conducted in Mexico, ear size and kernel number drastically increased over time with plant height while the number of leaves and stalks decreased and seed casings disappeared (Kingsley, 2005, University of Utah 2012). Figure 2. Teosinte, Corn and hybrid. Although this information seems obvious today, no records were kept for these initial crosses, and only through scientific experimentation have researchers discovered the evolutionary history of this plant. Modern day maize and teosinte are genetically compatible and modern day hybrids between them have characteristics of both and are fertile (Figure 2). Controlled crosses in over 50,000 plants conducted by George Beadle indicated that the genetic differences between teosinte and maize comprise between 4-5 genes. Additional research through the introduction of mutations into maize genomes give modern maize plants characteristics of teosinte, which confirm Beadle s initial results (Kingsley, 2005, University of Utah 2012). A second example of the power of artificial selection and directed evolution exists today in the form of man s best friend dogs. Fossil records reveal that dogs have been associated with humans for over 130,000 thousand years and recognizable changes and selection for certain traits can be recognized in ancient Egyptian dog fossils. Initial fossils resembled today s wolves, and the Egyptians selected for sleeker and more sophisticated looking traits that look like today s saluki breed. Today s dog breeds vary in size, coat color, number of teeth, leg length, snout size, ear size, and a seemingly infinite number of additional characteristics. In fact, Charles Darwin Page 2 of 6
pointed out that the skeletons of modern dogs are so different that if they were found in the fossil record today, they would likely be considered a different species (Figure 3) (Kingsley, 2005, University of Utah 2012). In the 1920 s and 30 s, Charles Stockard purchased a farm (Cornell Anatomy Farm) and conducted breeding experiments, using some of the modern breeds that had differential traits. Stockard found that the genetics of individual traits seems to be relatively simple. He also concluded that different genes seemed to control the growth of different bones, as well as the fact that artificial selection seems to be able to Figure 3. Popular Dog breeds of 1912. drastically change phenotypes in relatively few generations (Kingsley, 2005, University of Utah 2012). In addition to artificial selection, which is a deliberate selective force that humans have introduced, we as a species have unintentionally caused many other organisms to evolve through the use of antibiotics. Antibiotics include a variety of medications prescribed to combat bacterial infection and are often prescribed liberally by doctors for patients who are exhibiting signs of a bacterial infection. Today, you may see antibacterial products such as soaps, towelettes, and hand washes. What many do not Page 3 of 6
realize is that this liberal use of antibiotics is driving bacteria to evolve a resistance to these products, and the end result could be deadly. Antibiotics were first discovered in the 1929 by Alexander Fleming. Fleming noticed that bacteria failed to grow in a Petri plate, which had been taken over by a species of bread mold called Penicillium (Figure 4). This led Fleming to conclude that the mold created some substance that could kill certain strains of bacteria. By the 1940s, subsequent research led to the wide use of this compound (called penicillin) by the general public to combat bacterial infection and sickness (Fisher 2012). The success of penicillin is impressive, and after its initial discovery, it was hailed as a miracle drug. However, the discovery of penicillin was only the beginning, and today there are Figure 4. Penicillium over 100 types of antibiotics and over 150 million antibiotic prescriptions are written each year (Stephens 2012). Despite this great success, recent discovery of new antibiotics has slowed greatly, and recent research only seems to improve existing antibiotics (BBC News 1999). Figure 5. Staphylococcus aureus In addition to the lack of antibiotic breakthroughs, a disturbing trend of antibiotic resistant bacteria is on the rise. As early as the 1940s, certain strains of bacteria such as Staphylococcus aureus (which causes skin infections) were found to be resistant to penicillin (Fisher 2012) (Figure 5). Over time, doctors are noticing more and more infections that Page 4 of 6
are becoming increasingly difficult to treat. For example Klebsiella pneumoniae, which had infected a patient in an intensive care unit, was found to be resistant to every type of antibiotic that the hospital had (Groopman 2008). For the most part, these outbreaks seem to be confined to the places where antibiotics are used most often including hospitals and nursing homes. However, deaths from drug resistant bacterial infections are being reported in community settings including football teams and Hurricane Katrina evacuees (Groopman 2008). At this point, the only resistance against these bacterial infections has been our own immune system, which evolved long ago as a response to such infections. Perhaps it is not too surprising that the best defense against evolving strains of bacteria is a system that has been perfected over millions of years of evolution. Works Cited BBC News. 1999. A brief history of antibiotics. Retrieved from: http://news.bbc.co.uk/2/hi/health/background_briefings/antibiotics/ 163997.stm Fisher, M.C. The History of Antibiotics. Retrieved from: http://www.healthychildren.org/english/healthissues/conditions/treatments/pages/the- History-of- Antibiotics.aspx?nfstatus=401&nftoken=00000000-0000-0000-0000- 000000000000&nfstatusdescription=ERROR%3a+No+local+toke n Groopman, J. 2008. Superbugs. The New Yorker, Retrieved from: http://www.newyorker.com/reporting/2008/08/11/080811fa_fact_g Page 5 of 6
roopman. Kingsley, 2005. HMMI Holiday Lecture Series, Evolution: Retrieved from: http://www.hhmi.org/biointeractive/evolution/lectures.html Stephens, E. 2012. WebMD. Retrieved from: http://www.emedicinehealth.com/antibiotics/article_em.htm University of Utah, 2012. Learn Genetics. Retrieved from: http://learn.genetics.utah.edu/ Page 6 of 6