I remember in one of our class discussions, lactose intolerance came up and I thought that a change in the lactase (the enzyme that breaks down lactose or milk sugar) gene made it possible for expression after weaning. This meant that individuals could digest milk and other dairy products and supplement their diet with other sources of calcium and vitamin D. To me, that seemed a completely sufficient explanation for why the new allele for lactase was selected as advantageous. After all, we’re all told to drink milk to build strong bones, so why wouldn’t the same apply to early shepherds. This explanation is known as the “Calcium Assimilation Hypothesis.”

We need vitamin D to absorb calcium. That vitamin D can come from one’s diet or come from sunlight. So in geographic regions of less sunlight, there is a greater need for a diet containing vitamin D than say in equatorial regions. In other words, the Calcium Assimilation Hypothesis really only holds for northern European populations. 

From here on out, I think it’s important to consider lactose intolerance as more than the digestion of milk, or more specifically lactose, but as an evolutionary culmination of culture, geography, and sunlight. 

This article in the New York Times talks about how dust mites are proof that evolution does not always move forward but can actually regress. A study in the University of Michigan found that  the phylogenetic tree of dust mites shows that dust mites themselves are free-living organisms, and they evolved from parasites, and parasites evolved from free-living organisms. This article stood out to me because it reminded me of our discussion in class that covered how no one organism is the “most advanced,” but rather all organisms have evolved to be best fit to their particular environments. Understanding that concept,  I would suppose that a long time ago free living organisms were no longer a good fit for a certain environment and so after a long period, parasitic organisms evolved by natural selection. Then, in another environment, being a parasitic organism was no longer favorable and being free-living was a better fit, and so natural selection created the free-living dust mite.  Natural selection selects for organisms to fit their environments, there is no goal of creating the ultimate, perfect organism. If becoming a better fit for the environment means the return of a trait of an ancestral organism, the fact that the trait was previously discarded is irrelevant; that trait is now a good fit again.

To tie this in with medicine, the article concludes by saying that discovering the free-living nature of dust mites gives a new genetic insight into these organisms that will help scientists to understand how people with dust allergies react to dust mites, possibly leading to the production of a better allergy medication. If only there could also be some medical advancement in spring allergies too; it’s almost that time of year. Makes you wonder why evolution has not eliminated allergies in general: dust or pollen based.

The article’s link is below:

Many found it interesting that the prevalence of H. pylori infections did not correlate with cancer incidence. In a study of two Colombian populations, a coastal population of African ancestry had a low incidence of gastric cancer compared to a population of largely Amerindian descent in the Andes Mountains. By studying the tissue samples of patients from these populations, molecular biologists and researchers found out that the H. pylori strain affecting those in the coastal region were of African descent, while the H. pylori strain affecting the Amerindian human population were of south European descent. The results demonstrated that a “shared evolutionary history of humans and bacteria resulted in a less virulent host-pathogen relationship.”

“[It’s] fascinating,” said El-Omar. “If you have African strains affecting African-ancestry hosts, it doesn’t cause too much damage, whereas if you’ve got African-origins strains infecting Amerindians up in the mountains, that’s when you get most precancerous changes. So it looks like if you’ve coevolved with your strains, you get less and less virulence.”

This article didn’t go into too much detail about the evolutionary mechanisms so I did some more research on this host-pathogen coevolution. I found out that one explanation for why one population is more affected by diseases is tolerance evolution. The evolution of tolerance results in a changed selection on parasite populations, which can lead to parasite evolution despite the fact that tolerance is not directly antagonistic to parasite fitness. The evolution of tolerance is like our attempts of vaccination in order to decrease the prevalence of disease, without reducing parasite densities or eradicating the infection. These vaccinations can select for more pathogenic viruses, creating a greater risk for those unvaccinated who come into contact with these pathogens. Tolerant individuals also select for parasites with greater virulence, causing a more devastating effect on those intolerant who become exposed to the disease.

Link to article: http://www.the-scientist.com/?articles.view/articleNo/38845/title/Human-Pathogen-Coevolution/

Cancer is more common in older people than the young, and there is by no means agreement on why this is true. Antagonistic pleiotropy has been proposed as the genetic mechanism underlying life-history trade-offs. Dr. Sharpless studies the process of aging and its relationship to cancer and degenerative diseases. This is a video of an interview in which I think he does a good job to  explaining his research – both in mice and in humans. It’s long, but gives a good example of both scientific hypothesis testing and a bit of the history of this field.   

http://s3.amazonaws.com/thesciencenetwork/videos%2FGlenn2011%2FNorman+Sharpless.mov

This article contains a possible, evolutionary answer as to why all animals with a backbone and jaw develop with four limbs (based on the scholarly publication published by Laura Nuno de la Rosa). The hypothesis is that limbs develop in areas where the layers of tissue (during early development) are separated enough for an appendage to form-it just so happens that the location of the separations and their favorable interactions with other tissues allow those limbs to form. What struck me the most about the article was not its content but instead a line that reads,  “As with any long-standing question in evolutionary biology, numerous ideas have been proposed to explain different aspects of the origin of paired appendages in vertebrates” (Science Daily). This reminded me of our discussion in class about the importance of thinking through all possible hypotheses to these evolutionary or distal questions. Also noteworthy is a line in the article that reads, “…the focus of the hypothesis on global embryonic patterning and tissue interactions emphasizes the importance of accounting for factors other than genes (epigenetics) to understand development and evolution” (Science Daily). With that, the author emphasizes the importance of viewing evolutionary issues at a macroscopic level instead of only focusing on the microscopic, DNA level. That is certainly another interesting idea to keep in mind when considering our upcoming assignment…Here’s the link to the article. At the end of the text, there is a citation of the the scholarly publication the article is based on as well.

http://www.sciencedaily.com/releases/2014/01/140127112729.htm

Interestingly enough, this article entitled, Does Evolution Evolve Under Pressure?, in Wired Science magazine discusses a slight departure in the topics discussed Tuesday in class regarding understanding the concept of evolution and natural selection.  According to the article, Susan Rosenberg theorized that bacteria can self- mutate in the sense that they can, under pressure, induce increased rates of mutations in the hopes of finding an “escape route”.  This sort of theory straddles the lines between Darwinian and Lamarckian realms of thought: the grey area between self-mutation and trial and error. Some may argue that this is a form of artificial selection because the general course of evolution is not occurring – it is being tampered with by the organism itself. This then also begs the question that if this theory holds to be true, then what does this indicate for certain realms of study such as antibiotic resistance and the evolution of cancer? If scientists or researchers could somehow try to control for stressors that induce mutations in the first place, could that somehow impede the process of evolving antibiotic resistance and further change the practice of medicine and oncology? Ideally, if this theory holds to be true and applicable, evolution could not only be important to understand in medical education as an important framework and understanding why, but now could have direct implications to preventative medicine in terms of determining how. Doctors could advise against certain stressors that induce certain mutations in some bacterial infections or certain tumors (that can also develop antibiotic resistance).  The article also goes into further detail describing studies that were able to create conditions that induce organisms to mutate at higher frequencies. This theory largely remains controversial, and it would be interesting to look into how critics explain a reasoning behind the successes of these mentioned experiments. A link is provided to the article below: http://www.wired.com/wiredscience/2014/01/evolution-evolves-under-pressure/

Move over evolutionary medicine and make room for evolutionary veterinary medicine. Actually, it seems vets have had a handle on using evolutionary reasoning for quite some time. For example, fecal transplants to restore micobiome health after C. diff infection is an established technique for cattle! Perhaps this explains why my terrier looks at week old dog poop on the sidewalk like he just found buried treasure. The website has loads of great resources and articles: www.zoobiquity.com

There are more courses in evolutionary medicine now than ever. Here is a link to a list of undergraduate and graduate course syllabi on the topic. Our course syllabus in posted on blackboard. How does it stack up? What topics from similar courses would you like to see covered? In general, this is also a great resource for finding presentation topics and ‘poaching’ papers to post and discuss on our blog.

Welcome to the course blog for biol285: Evolutionary Medicine. This is a space for students and others to discuss topics relating to the interface of evolutionary biology, human health, and disease.

Course details, including the syllabus and required for class discussions will be posted on blackboard.