Caroline Turner

Caroline Turner

Dolby : Freshman Seminar “The Human Animal”

November 18, 2008

Mate Choice/Sexual Selection

A main fear of practically every human being is ending up alone or alienation from a social norm. Sexual selection, which influences mate choice, is based off of the Darwinian theory of the survival of the fittest. A stereotypical preoccupation of many young men and women is finding a lifelong partner, or a monogamous mate. One typically determines the attractiveness of a potential mate, and therefore develops interest, based on physical appearance. Scientific findings suggest that as a species, humans like their prospective partners to be slightly different in physical appearance, but still quite similar (Love’s a Fight Between the Eyes and the Nose, 2005). Biologically, the phrase “beauty is in the eye of the beholder” appears to hold true.

Natural selection forces a competitive interaction between members of the same sex to fight for the mate with the “best” genes. Typically those with genes considered to be superior have particular traits that allow them to receive more resources; this could include being the fastest, the strongest, or the biggest. In most mammalian species, including humans, the male is the one who must compete for the mating rights of the female. For this reason, females have the ability to be more selective in the mating process. Biologically, this can be explained because the availability of female sex cells is a limiting factor in reproduction and once fertilized and the gestation period is significant. Males, however, have the ability to produce millions of sperm cells and can impregnate an almost infinite number of females—therefore passing on his genes to a maximum number of offspring. However, in animals such as birds, it is the female that pursues the male. For this reason, the male is often a bright color or specially ornamented. The female bird is typically bland in appearance. An exception to this can be found in the lazuli bunting, a bird species that displays a rare evolutionary pattern, disruptive selection, in which opposite extremes of a trait are favored (Dull Birds and Bright Ones Beat So-So Guys, 2000).

A biological component to determining attractiveness has been related to the sense of smell. The sweaty tee shirt experiment, a process in which researchers gave a group of women a selection of shirts worn by men and then asked the female participants to rate the attractiveness of the men solely based upon the smell, lead scientists to believe that the MHC gene influences mate selection. MHC, major histocompatibility complex, is the most diverse of all genes and described by Richardson as “differ[ing] so widely that they constitute a molecular John Hancock, one that helps organisms recognize their own healthy cells, identify pathogens, and reject foreign tissue” (Scent of a Man, 1996). A similar experiment was also carried out with mice, which led to the conclusion that individuals are attracted to other mice with variants of MHC genes different from their own. The mice tended to confirm this preference by mating with mice possessing different MHC genes (Love’s a Fight, 2005). An interesting development discovered by the use of mice in MHC experimentation was that the female mice preferred mates with different variants of MHC genes until pregnant, when they begin to prefer the company of mice with similar genetic makeup. The participating scientists theorize that this is because the female mice prefer to nest with relatives to ensure maximus survival of offspring (Scent of a Man, 1996). This theory can be applied to human females, although it invokes question over whether women taking birth control pills, which mimic pregnancy in the body, become sexually attracted to men with similar MHC genes. The currently applied theory regarding the MHC gene’s influence on sexual attraction is that there is an evolutionary advantage to choosing partners with dissimilar genes. Choosing a mate with different MHC genes than oneself serves three purposes: increasing fertility, producing hardier offspring and maximizing their chances of survival, and reducing the rate of genetic disease caused by inbreeding (Scent of a Man, 1996)(Love’s a Fight Between the Eyes and the Nose, 2005).

There are several physical patterns that affect the physical “attractiveness” of an individual. Both genders have been found to prefer mates that have visually symmetrical faces and bodies (Love at First Sight?, 2003). Women typically find different elements of the male face to be attractive based on their stage in their menstrual cycles. During ovulation and briefly afterwards, women have an increased preference for facial configurations that convey dominance, meaning features that are considered masculine, while they prefer more feminine characteristics at other points of their cycle. Experimentation indicates that men’s concepts of attractiveness remain relatively constant (Love at First Sight?, 2003). While women tend to be attracted mainly to facial characteristics, men tend to prefer the bodily characteristics of women, such as hip-to-waist ratio. This can be explained in an evolutionary manner as being an outward sign of fertility.

In addition to the purely physical indicators of attractiveness of a potential mate, the behaviors of humans during “courtship” can influence the opinions of those an individual wishes to impress. Dating rituals help individuals obtain a mate by either showing their evolutionary fitness to potential mates to evaluate the fitness of a potential mate (Mating Games: Cultural Evolution and Sexual Selection, 2007). Darwin’s sexual selection theory states that most cultural practices and social interactions have a competitive element. Participating or excelling in such activities often is used as tactics to impress members of the opposite sex. One’s status, typically obtained or influenced by participating in cultural and social activities, including resources, longevity, and good genes, increase an individual’s attractiveness and value as a mate (Mating Games: Cultural Evolution and Sexual Selection, 2007). One could easily argue that almost every action is performed in attempts to impress a prospective mate. Many activities are culturally invented as indicators of bodily and psychological fitness. A few such activities include football, chess, bungee jumping, and intensely following a sports team. These activities, respectively, can indicate physical health, intelligence, courage, and loyalty; all socially desirable traits in a mate (Mating Games: Cultural Evolution and Sexual Selection, 2007).

Darwin’s theory involving sexual selection also categorizes the efforts of individuals to obtain a mate as either intersexual or intrasexual selection. Intersexual selection serves as a mean to impress members of the opposite sex in attempts to find a mate, while intrasexual selection helps one obtain a higher position in the hierarchy of one’s own sex. Anderson De Block correlates the two divisions as “intersexual selection and intrasexual selection are conceptually related in that mate preferences exerted by ones sex should influence the resources over which intrasexual competition occurs in the other sex”. Sexual selection is often the element of Darwin’s theory that is argued with. He defends his theory by stating, “The ornaments [of males] and their glands for emitting odors” as “serving only to allure or excite the female”. This is a clear indicator of the validity of his theory because sexual selection was implemented by females because “unornamented or unattractive males would succeed equally well in the battle for life” (Female Song Sparrows Prefer Males That Learn Well, 2002). Sexual selection is a valid theory because individuals choose others to mate with, in many cases, for reasons that do not affect evolutionary success.

Darwin’s theory of sexual selection has been further investigated and experimentation has been performed to supplement validate his findings. Swedish biologist Malte Andersson used African peacocks to confirm that Darwin’s theory was applicable to other animals as well. In his experiment, used differing tail lengths of the male birds and observed the amount of mates each male peacock obtained. In accordance to Darwin’s theory of sexual selection, the peacocks with the longest tails attracted the largest number of mates. Logically, the theory of sexual selection makes sense. Theory indicates that “one sex must evolve some trait, and the other sex must evolve in lockstep a liking for that trait”; which is evident in animals including lions, baboons, and peacocks.

A biological approach to understanding the topic of mate choice would be greatly beneficial to society, as most of human adult life is consumed with developing, maintaining, or discovering a monogamous relationship with another person. Hypothetically, if one had a solid understanding of the biological influences involved in mate choice, one could find a life-long partner more efficiently. This could also help determine one’s “type” from a biological standpoint, as opposed to through trial and error. It would also virtually eliminate the heart break many individuals go through while trying to find a successful mate.

Badyaev, A. V., et. al., Avian Sexual Dichromatism in Relation to Phylogeny and Ecology. Annual Review of Ecology, Evolution, and Systematics v. 34 (2003) p. 27-49

Coghlan, Andy. “Love’s a fight between the eyes and the nose.” New Scientist 187 (2005). Wilson Web. University of Mary Washington, Fredericksburg. 17 Nov. 2008 <http://vnweb.hwwilsonweb.com/hww/results/results_single.jhtml;hwwilsonid=

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De Block, A. “Mating Games: Cultural Evolution and Sexual Selection.” Biology & Philosophy 22 (2007): 475-91.

Diamond, J. 1992. “The Third Chimpanzee.”

Douglas, K. “Love at First Sight?” American Scientist 91 (2003): 120-21.

Hardling, R., et. al., Male Mating Constraints Affect Mutual Mate Choice: Prudent Male Courting and Sperm-Limited Females. The American Naturalist v. 172 no. 2 (August 2008) p. 259-71

Milius, S. “Dull Birds and Bright Ones Beat So-So Guys.” Science News 227th ser. 158 (2000): 277.

Milius, S. “Souping up the Eggs if the Dad’s Hot Stuff.” Science News 156 (1999): 283.

Richardson, S. “Scent of a Man.” Discover 7 (1996): 26-27.

Yasukawa, K. “Female Song Sparrows Prefer Males that Learn Well.” Bio Science 52 (2002): 1064-065.

Tags: human evolution

Some have expressed concern over UMW’s lack of diversity among its students, faculty, and staff.  What should UMW’s priorities be in increasing its diversity, and by which criteria should our concept of diversity be based?

                The University of Mary Washington was recently given a nickname by the Princeton Review based not on its academic or athletic achievement, but on the apparent lack of diversity throughout its student body.  In 2003, the publication listed the university as the “most homogenous in the nation”.  Based off this standing, the University of Mary Washington was given the nickname, the “University of Mostly White”. (Boorstien, 2005) Statistically, this name is appropriate—as eighty-eight percent of the student body is Caucasian and a mere fourteen of the incoming freshman class were self-labeled as African-American. (Boorstien, 2005)

                Historically, race is perceived as a huge issue in our society.  As most are aware, Americans in the past were very race selective—even forcing individuals into slavery based on skin color. From appearance alone, one can distinguish between the races.  But biologically, race is a non-factor and cannot be distinguished through use of DNA.   Traditional scientific language uses the term race as a synonym for sub-species, when in reality; recent scientific experimentation has shown that distinctive genetic differences do not exist between appearance based “races”.   (Brownlee, 2005)

                In current society, many jobs and schools practice affirmative action, which is the preferential hiring or accepting of people based solely on their minority status.  Recent scientific experimentation regarding race undermines the fairness of this practice.  How fair is affirmative action if there exists no real difference between the races? The University of Mary Washington has been placed under pressure to further diversify their student population.  This has been meant to mean that the school should increase the number of typically under-represented minority groups, including African American, Asian Americans, along with others.   However, diversity is not only dependent on race.  Differences in the student body can also be attributed to the location in which the student was raised, sexual orientation, genders, religion, and interests. 

                In my opinion, instead of race based affirmative action, the University of Mary Washington should try to increase diversity based on geographical location and socioeconomic status.  While it is understandable that many attribute diversity only to race, the lack of genetic difference between races indicates that a broad range of races does not really indicate a diverse student body. 

                A main goal of the admissions process of any college or university is to increase fairness to minorities, because typically this group of people comes from a distinct disadvantage.  However, there are always huge exceptions to this basis of thought.  There are plenty of African Americans with a high level of education and earning power, including Oprah Winfrey and Barack Obama, and Caucasian Americans raising children in poverty.  As an established and successful university, UMW should be focused on granting admission to intelligent students with a high possibility of success in a college setting. 

                I think that the university should be focused on accepting students with a high probability of success, without a quota system based on race.  However, to promote diversity, I believe that university sponsored cultural activities are a good idea.  Acceptance of and learning about cultures other than one’s own is a good way to diversify the student body. 

 

 

 

Boorstein, Michelle. “Community Calls for Diversity.” The Washington Post. 3 Apr. 2005. 16 Oct. 2008 <http://www.washingtonpost.com/wp-dyn/articles/a22069-2005apr2.html>.

Brownlee, Christen. “Code of Many Colors.” Science News (2005).

Stem cells can become a wide variety of different types of specialized cell types.  By saying “do i have to declare a major? Couldn’t I just be a stem cell?”, the student is saying that he would rather be able to switch and choose a major without making a permanent decision.

Evolution theory dictates that humans and chimpanzees both evolved from a common ancestor hundreds of thousands of years ago. A common misconception is that humans evolved in a linear fashion. Hallman states that evolution is traditionally, although incorrectly, “illustrated as a parade of fossil hominids, with the specimens in the parade becoming more modern as they march across the page”.  Instead, humans evolved in a branching manner.  Several species of hominid coexisted at the same period of time, although only Homo sapien sapien, modern humans, exist in current day.  There were at least four separate species that eventually led to the modern human, including Homo ergaster, erectus, heidelbergenis, and neanderthalensis.  

Because of the transition from hominids being quadrupeds to gaining the ability to walk upright on two legs, muscle location and size has changed during evolution.  Two muscles in particular that differ from early hominid to modern human are the gastrocnemius (calf muscle) and the gluteus maximus (posterior muscle).  Evolutionary theory proposes that bone length and muscle position slowly changed to allow for ease in movement; particularly running (Bramble and Lieberman 2004).  

The currently trusted evolutionary theory indicates that brain size, therefore head size, has increased drastically.  Hominid head size exponentially increased with an increase in physical size.  According to Rose (2006), the braincase volume of modern humans has increased from 400-500 cc, in early upright hominids, to 1000-2000 cc.

            Still in reference to size, early hominids were significantly smaller than their modern predecessor.  Homo habilis, an early hominid, grew to be only about 1.0 meters tall, while a modern human (Homo sapien sapien) have height ranges of 1.1-1.9 meters.   Similarly, the average mass of a Homo habilis fell in the range of 30-55 kg and a Homo sapien sapien typically ranges from 55-80 kg (Foley 2004).  However, this is not reflected in the drawing, as the only obvious body size change is from the third drawing to the modern human (Foley 2004). 

Foley, Jim. “Homonid Species.” Talk Origins. 31 Oct. 2004. 20 Sept. 2008             <http://www.talkorigins.org/faqs/homs/species.html>.

Rose, M.R. and Mueller, L.D. 2006. Evolution and Ecology of the Organism. Pp. 601-623.            Pearson Prentice Hall, New Jersey.

 

 

Disease can be caused by either environmental or genetic factors; but typically the development of disease arises from a combination of the two.   A genetic disorder is caused by abnormalities in genetic material.  There are four subcategories of genetic disorder including: single gene, multifactorial, chromosomal, and mitochondrial. 

                There are 6,000 single gene disorders, examples including cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington’s disease, and hereditary hemochromatosis.  Such a disorder occurs in about one out of every two-hundred births.  A single gene disorder is caused by changes in the DNA sequence of one specific gene.  When a gene is changed, or mutated, a genetic disorder typically results. 

                A multifactorial genetic disorder is caused by a combination of environmental factors and changes in multiple genes.  Because a mutation occurs on many individual gene strands, a multifactorial disorder is much more complex to analyze and diagnose than a single gene disorder.  Examples of multifactorial genetic disorders include heart disease, high blood pressure, Alzheimer’s disease, diabetes, cancer, and arthritis. 

                Chromosomal changes usually result in genetic disease.  Chromosomes are carriers of DNA, genetic material, and mutations including change in chromosome number can be devastating for the body. An example of chromosomal genetic diseases includes Down Syndrome.

                The least common type of genetic disorder is due to mitochondrial mutation.  Mitochondria are considered to be the “power-house” of the cell, and when changed, can cause disaster to the functioning mechanisms of the cell.

                Cystic fibrosis is the most common genetic disorder currently.  Roughly five percent of the United States population carries a copy of the damaged gene. 

Tags: biol12108sec3

The birds are examples of the biological principle of adaption.  Their beaks are curved so that they can crack nuts and shells–a large element of their diet. 

http://www.littlerockzoo.com/edzoocation/adapt.html

Tags: biol12108sec3