Spring 2009

spring 2009

Note from the Editorial BoardThe Dartmouth Undergraduate

Journal of Science aims to increase scientific awareness within the

Dartmouth community by providing an interdisciplinary forum for sharing undergraduate research and enriching

scientific knowledge.

EDITORIAL BOARD

President: Shreoshi Majumdar ’10Editor in Chief: Hannah Payne ’11Managing Editor: Jay Dalton ’12Managing Editor: Shu Pang ’12

Design Managing Editor: Colby Chiang ’10Asst. Managing Editor: Rebecca Lee ’12

Layout Editor: Alex Rivadeneira ’10Online Content Editor: Alison Flanagan ’10

Public Relations Officer: Victoria Yu ’12Secretary: Marietta Smith ’12

DESIGN STAFF

Jocelyn Drexinger ’12Katherine Fitzgerald ’11

STAFF WRITERS

Elizabeth Asher ’09Laura Calvo ’11

Edward Chien ’09Nicole Ilonzo ’10Heewon Kim ’10

Diana Lim ’11Jennifer Liu ’12Sharat Raju ’10Yifei Wang ’12Ian Webster ’11

Aviel Worrede-Mahdi ’12Hee-Sung Yang ’12Sunny Zhang ’10Jingna Zhao ’12Peter Zhao ’10

FACuLTY ADVISORS

Alex Barnett - Mathematicsursula Gibson - Engineering

Marcelo Gleiser - Physics/AstronomyGordon Gribble - ChemistryCarey Heckman - Philosophy

Richard Kremer - HistoryRoger Sloboda - Biology

Leslie Sonder - Earth SciencesMegan Steven - Psychology

SPECIAL THANKS

Dean of FacultyAssociate Dean of Sciences

Thayer School of EngineeringProvost’s Office

Whitman PublicationsPrivate Donations

The Hewlett Presidential Venture FundWomen in Science Project

[email protected] CollegeHinman Box 6225

Hanover, NH 03755(603) 646-9894

dujs.dartmouth.edu

Copyright © 2009The Trustees of Dartmouth College

Evolution is a gradual, almost imperceptible process, but it is responsible for life on earth as we know it.

Ever since the first pre-biotic, self replicating molecules began to form in shallow tidal pools billions of years ago, life has evolved into countless species, almost all of which are now extinct. Still, the remaining diversity is staggering, and we, as humans capable of destroying that diversity, are responsible for maintaining it.

Charles Darwin’s pioneering research in the Galapagos Islands led to his landmark 1859 work, On the Origin of Species that presented the theory of natural selection. Today modern evolutionary synthesis is widely accepted by evolutionary biologists.

Not only is evolution responsible for the remarkable diversity of life but we have also turned its power to our advantage through artificial selection, allowing us to domesticate crops and animals and screen for genetically engineered antibiotic-resistant bacteria in standard molecular biology protocols. However, outside of the laboratory, resistant bacteria pose a constant challenge as they rapidly evolve to escape drugs.

One of the main questions in evolutionary biology concerns the origins of our species. In this issue, Laura Calvo ’11 explores four fascinating aspects of human evolution. Heewon Kim ’12 discusses the bizarre phenomenon of hiccups, and Shu Pang ’12 reveals the surprising health benefits of altruism.

The study of evolution tells us much about our past, but what about the future? It seems that all organisms are destined for extinction eventually. Victoria Yu ’12 explores various ends to the human race, whereas Nicole Ilonzo ’10 ruminates on the coevolution of humans and computers.

The teaching of evolution has historically been a controversial topic, especially in the u.S. Marietta Smith ’12 reveals that Dartmouth deviated from the norm by encouraging the teaching of evolution well before the infamous Scopes trial.

Across interdisciplinary borders, Cynthia Kahlenberg ’10 analyzes the impact of Prince Leopold’s hemophilia, and Shannon Hextrum ’09 explains our innate fear of exceedingly human-like objects.

Finally, exceptional undergraduate research is highlighted in Yiran Gu’s ’09 analysis of the relationship between figs, fig wasps, and fig wasp parasitoids, as well as the observation of pool disinfectant by-products by Dillon Lee ’08, Curtis Hansen ’10, Shahen Huda ’10, and Jie Xu ’10.

We hope that you enjoy this issue of the DuJS, discovering where we come from and perhaps where we are going.

Dartmouth unDergraDuate Journal of science6

meDicine

A Twist to TumorsHow Overzealous Cancer Screening May Hurt Us

Jingna Zhao ‘12, duJs staff

Among all the battles we fight with cancer, one has gained the most public attention is breast cancer.

Yet, after years of research and millions of dollars in funding, one in eight wom-en will still be diagnosed with breast cancer in her lifetime (1). The best de-fense we have so far against this mal-ady is early detection through regular mammogram screenings. However, the treatment of breast tumors may be rev-olutionized by a recent study published in the Archives of Internal Medicine, where H. G. Welch claims that tumors may disappear without treatment (2).

Today, there are about 34 mil-lion mammogram procedures per-formed in the u.S. each year (3) and the FDA recommends that all women over the age of 40 get regular screen-ings once every year (4). Once a woman is suspected of having cancer due to a positive mammogram result, she un-dergoes various tests, biopsies, and sometimes surgeries to follow up. Five to fifteen percent of mammogram stud-

ies require additional mammograms or ultrasound tests because of abnor-mal results, and if follow-up studies still result in suspicious findings, the next step is to perform a biopsy (5).

Biopsies are usually performed by using a needle to take out a sample of tissue for a pathologist to analyze for malignancy. This is the only sure way to diagnose cancer. Four out of five biopsies are noncancerous (6), but many patients are subjected to much unnecessary stress throughout the testing process. Studies have shown that women experience long-term as well as short-term anxieties after re-ceiving a false-positive diagnosis (7).

Researchers are trying to find ways to ameliorate and perhaps eventually circumvent this imperfect method of treating breast cancers. As seven to eight percent of women aged 40-49 who have annual mammograms undergo breast biopsies, the majority of which are be-nign, Welch’s recent study could have potential benefits for many women.

MethodsIn Welch’s study, entitled

“The Natural History of Invasive Breast Cancers Detected by Screen-ing Mammography,” two groups of women aged 55-69 were observed, a screened group and a control group of about 100,000 women each.

The screened group under-went three rounds of mammogram screenings throughout the years 1996-2001. Once an invasive cancer was diagnosed, the patient imme-diately received treatment and the case was counted towards the total number of cancerous findings in the group. The control group was ob-served through the years 1992-1997 and was administered a one-time prevalence screen at the end of those six years. The total number of inva-sive tumors of the screened group collected through the three rounds was compared to the one-time prev-alence screen of the control group.

Image courtesy of the National Institutes of Health.

A woman receiving a mammogram at a clinic. DMS prof. H. Gilbert Welch argues that mammogram screenings might do less good for women than we believe.


In 1871, English naturalist Charles Darwin published The Descent of Man, and Selection in Relation

to Sex as a follow up to his renowned 1859 work on evolutionary theory, The Origin of Species. In the introduction of The Descent of Man, Darwin states that “the homological structure, em-bryological development, and rudi-mentary organs of a species, whether it be man or any other animal, to which our attention may be directed, re-main to be considered; but these great classes of facts afford, as it appears to me, ample and conclusive evidence in favor of the principle of gradual evolution” (1). Although at the time Darwin’s reinforcement of the idea of human evolution from a primate lin-eage was a controversial stance, over the past century the model of natural selection and gradual evolutionary theory has been solidified as a basis for evolutionary biology and physical anthropology. Recently, important as-pects of human-specific evolution have been revealed. Here, four interesting landmarks in the descent of Homo sapiens are outlined and their origins investigated. These include Homo sa-piens sapiens speciation, the FOXP2 gene, lactose tolerance, and childhood. Although these topics are still being explored, these recent research break-throughs have provided further insight into the topic of human uniqueness.

Models for H. sapiens sapiens Speciation

For many years, it was assumed that extinct hominid species H. sapi-ens neanderthalensis, or “Neander-thal man,” had traveled a separate evolutionary path from anatomically modern humans. The extinction of Neanderthals was attributed to simple natural selection, an idea supporting the replacement evolutionary model

evolution

Retracing the Descent of ManMajor Landmarks in Human-Specific Evolution

Laura CaLvo ‘11, duJs staff

of H. sapiens speciation, which states that modern humans originated in Africa and dispersed, replacing any other hominid species that existed in the world. The multiregional evo-lutionary model of H. sapiens spe-ciation supports the hypothesis that the ancestral species H. erectus first dispersed out of Africa to different areas of the world, so that differ-ent regional populations developed down their own evolutionary path.

Yet, a more prudent model has since been developed in light of ge-netic evidence in the modern human population. The assimilation model provides a middle ground between the multiregional and replacement models, explaining that there may have been several dispersions out of Africa, and that regional populations most likely interbred with other existing hominid species. This hypothesis is supported by several pieces of morphological evi-dence, such as the discovery of a skel-eton displaying both Neanderthal and anatomically modern human physical traits, the existence of the ancestral shove-shaped incisors trait in some modern Asian populations, and the overall pattern of gradual reduction in Neanderthal anatomical traits in an-cestral European human populations. The most parsimonious explanation is that Neanderthals, as well as early H. sapiens known as Cro-Magnon Man, shared the same territory as anatomi-cally modern humans, and that there was considerable interbreeding be-tween these early human populations. This would lead to a large amount gene flow, and eventually these morpholog-ically distinct groups would become one species sharing the same gene pool. Genetic evidence, such as a high degree of regional DNA markers in the human genome, and the shared FOXP2 gene in Neanderthals and H. sapiens sapiens, also paint a picture of as-similation, rather than abrupt distinc-tion of our Neanderthal relatives (3).

Language and the FOXP2 Gene

Animal communication systems, such as signaling or sonar, are used by many non-human social animals. Yet, only humans have the ability to think abstractly, thus transforming signals into symbols. Grammar and syntax, which allows for the creation of an infinite array of new thoughts in the form of sentences composed of a finite vocabulary, is unique only in human language. The human capacity for lan-guage is still a major area of unknowns for evolutionary biologists. In 1996, a study of a language developmental disorder in a uK family lead to the dis-covery of a highly conserved human version of the gene called forkhead box P2 or FOXP2 (5). In this family and in others who suffered from the same rare disorder, scientists found that a genetic mutation in the FOXP2 gene caused se-

Image courtesy of Bacon Cph. Source: Cro-Magnons Conquered Europe, but Left Neanderthals Alone, PLoS Biology Vol. 2, No. 12, e449 doi:10.1371/journal.pbio.0020449

(Accessed 28 April 2009).

Recent archeological evidence has shown that Neanderthals and humans share the same form of the FOXP2 gene.

13spring 2009

vere language disabilities, both in the production and the comprehension of sentences. With comparative genetic analysis, it is known that the FOXP2 human genotype is a trait unique to humans. Although there is only a dis-crepancy of two amino acids in the hu-man FOXP2 gene and the chimpanzee FOXP2 gene, this amino acid sequence has been highly conserved. It is evident that this trait developed fairly recent-ly, within the last 200,000 years (5). However, recent archeological DNA analysis has shown that Neanderthals also possessed the human form of the FOXP2 gene. The FOXP2 gene is also associated with human morphology, mainly the lowering of the larynx and directing fine muscle development in the tongue and palate, two biological features necessary for producing the broad range of sounds associated with human speech (4). This could be key evidence for uncovering the selective pressures that lead to the conservation of the human-specific FOXP2 gene.

It is postulated that this genetic change was driven by morphological adaptation. As humans stood upright, the descent of the larynx was crucial to avoid choking during food consump-tion. Although the direct correlation be-tween FOXP2 and the development of human language is still unclear, many have postulated that the genetic histo-ry of this gene is key to determining a

timeline for the use of spoken language among humans. The most intriguing aspect is that this small genetic change may be associated with the large hu-man population growth about 50,000 years ago. Agriculture and subsequent urbanization may have only been pos-sible after the development of human language. Since our Neanderthal an-cestors also possessed the same FOXP2 genotype as modern humans, this could mean that this subspecies also had the capacity for human language.

Lactose ToleranceThe ability for certain human

populations to digest lactose, the sugar found in milk, is one example of the interaction between cultural and bio-logical evolution in human genetics. Although the consumption of dairy products is an accepted norm in West-ern societies, there are many individu-als in the world who are lactose in-tolerant, because they do not possess the genetic trait that triggers cells in the small intestine to produce a high level of the enzyme lactase. The earli-est humans, however, did not have the genetic makeup for lactose tolerance.

With the intensification of agricul-ture came a spread in the domestication of animals. In ancient Europe, livestock rearing became a staple of settled civi-lizations, and so dairy-farming prac-

tices took hold (4). In a response to the heightened level of lactose introduced to the diets of these populations, selec-tion favored a higher production of the lactase enzyme. Today, regional distri-bution for lactose tolerance in different genetic populations is correlated with the presence or absence of ancestral dairy farming. For example, individu-als descendent from peoples of Britain, Germany, and Scandinavia have high lactose tolerance, possibly linked to a cultural history of drinking unpro-cessed milk, whereas those of south-ern Europe, such as in Rome, where lactose-free dairy products such as cheese were more often consumed, lac-tose intolerance is more prevalent (2).

The Human ChildhoodThe developmental cycle of an or-

ganism is a fundamental determinant in natural selection in a species. The important differences between the hu-man life cycle and the developmental pattern of other mammals and primates serve as a template for understand-ing how human evolution is unique. For example, the childhood stage is an aspect uniquely present in the human life cycle. The juvenile stage, the time between infancy and sexual maturity, is longer in primates than in any other social species. However, humans also possess an additional three to four years of relatively slow physical growth that extends the juvenile period even longer (3). Human childhood, which typically lasts from ages three to seven, is a period of stagnant morphological development, but provides humans a unique opportunity for rapid men-tal growth. The extension of this pre-pubescent period may have allowed for greater intellectual growth during the elastic stage of development. The childhood stage gives humans a lon-ger learning period before autonomy is reached, so that cognitive abilities such as language, reasoning, and problem-solving skills can be expanded while simple biological needs, such as food, are still being provided by parents.

ConclusionHumans share 99.6 percent of

their DNA sequence with their closest

Image courtesy of the United States Department of Agriculture.

The diet changes associated with dairy-farming drove the evolution of lactose tolerance in adult humans.


living species, the chimpanzee. Yet, it is obvious that since the speciation of H. sapiens, humans have traveled down a distinct evolutionary path. Outlined here are just several key aspects that define human uniqueness. However, it is important to note that pure genetics cannot solely account for these evolu-tionary landmarks. Rather, analyzing the bio-cultural forces in the course of human pre-history is the best way to understand human evolution and continue the investigation Charles Darwin began over a century ago. References 1. C. Darwin, The Descent of Man and Selection in Relation to Sex (D. Appleton and Company, New York, 1871), vol. 1, pp. 1-8.2. J. H. Relethford, The Human Species (McGraw-Hill, Boston, MA, ed. 7, 2008), pp. 434-435.3. S. Stinson et al., Human Biology: an evolutionary and biocultural perspective (Wiley, New York, 2000), pp. 310-312.4. W. Haviland et al., Evolution and Prehistory: the human challenge (Wadsworth/Thomson Learning, Belmon, CA, ed. 8, 2008), pp. 134-136.5. J. Itzhaki, The FOXP2 story: A tale of genes, language, and human origins (The Human Genome Project, 2003; http://genome.wellcome.ac.uk/doc_wtd020797.html).

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issue of The Lancet, there is an almost full-page article on hemophilia, with no mention of Prince Leopold (17). It is unlikely that doctors were unaware of Leopold’s condition (many of Leopold’s doctors, including Jenner and Legg, were leaders in the field of hemophilia research and would have clearly been able to identify Leopold’s symptoms as those of a hemophiliac over the course of treating him). It is more probable that the editors of The Lancet were re-spectful of the Royal Family’s privacy.

The British Medical Journal, another leading medical journal, also published two articles in its April 5, 1884 issue relating to Prince Leopold and hemophilia. One is a simple an-nouncement of his death, which states that right before his death, he was “breathing very stertorously” and had a “convulsion, with his face drawn to one side and his hands clenched.” This article contains no other medical infor-mation and no direct mention of he-mophilia, but does end by stating, “The constitutional malady from which he suffered is the subject of a leader in the present member of the Journal” (18). The article to which this refers is titled “The Haemorrhagic Diathesis.” The terms haemorrhagic diathesis and he-mophilia were synonymous in the late nineteenth century and the two terms are used interchangeably throughout the article. This article begins by stat-ing, “The recent bereavement in the Royal Family will naturally turn the attention of the medical public to-wards the constitutional affection to which the illustrious deceased was subject.” The article goes on to give a final word on Leopold’s death as a re-sult of a fall due to a weakness in his knee that was probably caused by he-mophilia and an intracranial compli-cation that arose from this fall (19).

From these articles, it is clear that the medical public knew of Leopold’s hemophilia. The editors of these jour-nals probably assumed that doctors would be particularly curious about a disease that had recently killed such a high-profile member of society.

1880s peak in journal articles on hemophilia

In the 1880s, the decade of Leo-pold’s death, there was a huge spike

in the volume of literature published about hemophilia in the united King-dom (Figure 1). Of the articles pub-lished in the 1880s, the vast majority were case studies rather than reviews of the current literature (20, 21). Nineteen of the articles published in the 1880s mentioned the hereditary nature of he-mophilia and sixteen did not. This in-dicates a widespread knowledge of he-mophilia, but as previously mentioned, during this period medical information was not well disseminated, so many physicians may not have known about the hereditary nature of the disease.

During the 1880s, doctors started to speculate on the causes of hemo-philia on a more scientific level. In the British Medical Journal in 1882, C. Francis theorized that the excessive hemorrhaging could arise due to a lack of fibrin in the blood, which would in-hibit the blood’s ability to clot. In The Lancet in 1886, T. Oliver put forth a hy-pothesis about the mechanism that led to hemophilia. He wrote, “So far as the pathology of the disease is concerned, I believe the state of the blood and blood vessels and a defective control-action on the part of the vaso-motor centres are the important factors in its causa-tion.” Similarly, Legg theorized that the disease arose from poorly devel-oped blood vessels (8). Although twen-tieth-century doctors discovered that the latter two ideas were far from true, the fact that doctors were attempting

to come up with scientific explanations marked progress in the field of hemo-philia. Still, they were far from having a complete understanding of hemophilia.

Breakthroughs in hemophilia research after Leopold’s death

In the decade following Leopold’s death, significant breakthroughs in the treatment of hemophilia occurred. Sir Almoth Wright, an English medical scientist, made a great contribution to hemophilia treatment through his research on the coagulation of blood. Wright demonstrated in 1891 that the blood of hemophiliacs had a longer coagulation time than normal blood because of a deficiency of calcium in the blood. He recommended calcium salts as a possible treatment. Later research showed that calcium in fact had nothing to do with blood clotting; instead a deficiency of certain blood proteins causes hemophiliac blood to coagulate more slowly, but Wright can still be noted for his experiments in measuring coagulation times (22).

Following Wright’s work, in 1910, Scottish physician and scientist Thomas Addis reported that hemo-philia arose because of an “abnormality in the nature of the coagulation [that] arises as the direct result of the great prolongation of the time required for coagulation to complete itself” (23). Over the course of the next year, Ad-

Image by Cynthia Kahlenberg ’10.

Figure 1: In the 1880s, the decade of Leopold’s death, there was a peak in the number of articles published about hemophilia in Great Britain.

47spring 2009

of chloroform (5-6). EPA regulations in general aim to keep the number of excess cancer incidences to between 10-4 and 10-6 to provide a reasonable safeguard against cancer (7).

The target molecules of this project, bromoform and chlo-roform, are easily absorbed by both the body and the environ-ment. They typically enter the environment through disposal of the disinfected water, or as vapor because of their volatility. Va-pors can remain in the air with a half-life of one to two months. At the surface of the water, the haloforms decompose slowly due to the greater availability of oxygen. under anaerobic con-ditions, commonly found in underground water sources, degra-dation of these molecules occurs more rapidly. Although these compounds are mobile in soil and seep into ground water, there is no evidence of their bioaccumulation in fish. Likewise, they easily enter the human system through inhalation, absorption, and ingestion, but 50-90% is removed within eight hours (8).

A summary of notable health effects and other physi-cal constants of these two substances are provided in Table 1.

MethodsLaboratory methods

Experimental methods were primarily adapted and taken from Hardee et al. (10). First, a calibration curve was made for chloroform concentrations ranging from 15 to 40 ppm via se-rial dilutions with deionized water. The chloroform was origi-nally 200 µg/L in methanol (Supelco, Bellefonte, PA). A mass of 1.75 g of sodium chloride (NaCl) was introduced to each amber vial of chloroform solution along with a magnetic stir-ring bar. The addition of salt enhances the partitioning of an

organic compound to favor the organic phase on the fiber (10).After conditioning a solid-phase microextraction (SPME)

syringe (75-µm Carboxen/polydimethylsiloxane fiber, Supel-co) for one hour at 250°C, the vapor in the headspace above the chloroform solution was extracted for a time period of 30 minutes at ambient temperature. Samples were sealed us-ing a screw cap containing a PTFE-faced rubber septum. The vials were clamped onto a magnetic stirring plate and the SPME assembly was secured in place above the vial cap (10).

Following a 30 minute extraction period, the fiber was im-mediately retracted and transferred to the injection port of the gas chromatograph. Chromatographic analysis was performed using a Hewlett-Packard GCD Plus GC–MS system. The initial oven temperature was set at 40°C for 5 minutes, ramped at 7°C/minute to 150°C, and held for 2 minutes. The analytical column was an HP-5, dimethylsiloxane (30 m x 0.10 mm i.d. x 0.2 µm film thickness). Predrilled septa (Supelco) were used and samples were desorbed under splitless conditions with helium as the carrier gas. Quantification of analytes was per-formed by measuring the peak areas of the analyte in pool wa-ter samples with respect to the calibration experiments (10).

Field methodsSamples were collected in triplicate in amber 15 mL vi-

als, with minimal air inclusion (See Table 2 for sample loca-tions). At all locations except Storrs Pond, Storrs Pool, Ci-ambra’s pool, and Dartmouth pool, samples were collected at the surface of the water, and at a depth of approximately five feet (1.5 m). At the aforementioned locations, samples were collected only at the surface. upon collection of the samples, air temperature and surface water temperature were measured, and current weather conditions recorded.

Samples were analyzed as soon as possible after col-lection, from a couple of hours to a few days. When not in transit or being analyzed, chloroform standards and pool samples were stored with NaCl in 5 mL quantities at 4°C. While in transit, samples were kept in a cooler at a temper-ature near 0°C for a time period not exceeding 90 minutes.

Results To quantify the amount of chloroform found in

pool water, a calibration curve was established relating ab-solute concentrations of chloroform to area under the GC peak. The calibration curve constructed from the stan-dards for chloroform in deionized water is presented below.

Seven of the eight pools sampled tested positive for ha-loforms (six contained chloroform, and one contained bro-moform). No pool contained measurable amounts of both haloforms. The concentration of chloroform found in the pool water varied from none detected to as high as 1.28 ppm. Neither of the two natural bodies of water contained any haloforms.

In all cases where data for haloform concentra-tion at deeper water is available, average haloform con-centration was greater in deeper water, compared to the surface. Only in Gribble’s pool, however, was this differ-ence statistically significant (t

calc = 6.95, n = 4, CL = 95).

Identification of the compounds was performed using a combination of data from the gas chromatogram as well as the mass spectra. Overall, both chloroform and bromoform exhibited a characteristic mass spectrum, and chloroform was detected at approximately 4.1 minutes by gas chromatog-raphy while bromoform was detected around 13.5 minutes.

Figure 2: Formation of toxic gases and vapors from chloroform.

Figure 3: Calibration curve for chloroform.

Spring 2009

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