Daily Archives: April 25, 2014

The Drunken Monkey Hypothesis

The topic I chose for my oral presentation recently came back in the news, with the publication of the book The Drunken Monkey: Why We Drink and Abuse Alcohol by Dr. Robert Dudley, a professor of biology at the University of California Berkeley. The book goes into greater detail about the hypothesis I discussed in class about alcoholism stemming from the consumption of fermented fruit. The theory, which Dudley refers to as a the “Drunken monkey hypothesis,” proposes that our tendency to favor alcoholic drinks and become addicted to them stems from the fact that humans have developed a powerful sensory bias towards alcohol that relates it to nutritional reward. As detailed in an article in The Huffington Post by Dudley, titled “How Evolution Explains Why Humans Drink and Abuse Alcohol.” Primates would have eaten fruit living in more tropical climates, which would have exposed them to more rapidly ripening fruit that contains ethanol due to fermentation. The consumption of these fruits by primates and our subsequent evolution from them suggest that we may have developed a genetic adaptation that primes us to want to consume more of it. It makes sense that early primates would have been drawn to this as a food source in the first place – fruit flies were the first ones to figure out that the smell of alcohol indicated a good source of calories, and alcohol stimulates feeding in modern humans through the aperitif effect (apéritifs are alcoholic drinks that are served before meals to stimulate the appetite).

The drunken monkey hypothesis points toward an evolutionary mismatch in humans with our modern consumption of much higher levels and concentrations of alcohol, especially with the evolutionarily recent process of distillation. Animals in the wild do not get drunk, since fruit contain very low levels of alcohol. But it leaves humans with the evolutionary results of being drawn to alcoholic substances.

Synopsis for Setchell

The article’s main question is: “what is the influence of major histocompatibility complex (MHC) on patterns of reproduction in the mandrill? The study also looked into the possibility of whether or not the males had a reproductive advantage via either superior competitive ability or via female choice within-male MHC diversity. This study is innovative because this particular study contained a large dataset, involving reproduction over multiple years for a long-lived species. This study was also the first to demonstrate a reproductive advantage associated with MHC dissimilarity in a polygynous species with high levels of male-male competition. This study supported previous studies showing significantly higher rate of nonsynonymous than synonymous substitutions within the mandrill DRB.

This study was done on a large, semi-free-ranging population of mandrills, at the Centre International de Recherches Médicales, Franceville. Observations of the female reproductive status, births, injuries, and disappearance were made daily. DNA was extracted from blood samples obtained during annual captures of the colony for genetic analysis. MHC-DRB genotyping was also conducted for 155 of the population. The overall genetic similarity between genotypes of two individuals was estimated in order to determine whether reproduction was biased towards unrelated partners. Measures of MHC dissimilarity were also calculated for each potentially reproductive dyad in order to determine whether reproduction was biased towards partners with dissimilar MHC genotypes. Various statistical analyses were done in order to answer questions such as, “does overall genetic dissimilarity influence reproduction?” or “does male genotype influence reproduction?”

After genetic analysis, the results suggest that the MHC sequences are capable of providing resistance to pathogens, and thus might be the foundation of MHC- associated mate choice. The results showed that that pedigree relatedness, overall genetic dissimilarity, MHC dissimilarity and male genotype all influenced reproduction in this mandrill colony. Results also showed that male rank was by far the strongest influence on reproduction in males, with alpha males being 18 times more likely to sire a given offspring than nonalpha males.

The findings show that MHC-associated mate choice may be more widespread than previously thought. The findings also suggest that individual genetic characteristics in mandrills may be linked to male vigour and further studies can be taken on to investigate whether microsatellite heterozygosity or MHC diversity are linked to better condition or reduced susceptibility to disease.

Hamiltonian Medicine article review

In this review, the authors explore the idea of Hamiltonian Medicine (HM). The driving force behind this idea is Hamilton’s theory of inclusive fitness, which incorporates the fitness of an individual and the effects said individual has on those that carry genes identical to the individual’s via descent. The authors argue that this is a theory that is widely accepted by the thinkers and practitioners of Darwinian Medicine (“the application of evolutionary concepts and tools to understand health and the causes and treatments of disease”), but is not systematically used as it ought to be in a number of contexts. Thus, the goal of their review is to show how HM can provide insights that have been missed/overlooked in the current Darwinian Medicine mode of thought. First, they describe three domains of social relationships covered in the scope of HM: 1) interactions between cells 2) interactions between genes and 3) interactions between humans. They then go on to describe six principles of HM, which all focus on the impact that interactions within and between the three aforementioned domains can have on human health. One example is the relatedness between microbes and the effect that this can have on virulence and transmission. This type of interaction also is dependent on how their hosts, in this case humans, behave, and thus the two domains of relatedness overlap to have a compounded effect on human health. They also point out how intragenomic conflicts and resource conflicts can have profound effects not just within societies but also within individual families. And lastly, they point out new ways of thinking about diseases such as cancer and mental illness. For example, cancer cells exhibit many similarities to microbes in an HM context, which could offer new perspectives from which alternative treatments might found. As a whole, HM seems to offer a very cohesive and profound insight to understanding human health in an evolutionary context. One of the challenges, which the authors mention, is that pursuing this kind of thought and research is going to be incredibly difficult and involved, because of the complex and interdisciplinary nature of this branch of thought and practice. Thus it will take time and experimentation for HM to effectively put into practice and to become a major branch of research. But, it seems that the knowledge and understanding that could come from pursuing it would be well worth the investment – as long as adequate funding and organization go into it.

A New Take on Why Babies Cry at Night

Babies have a tendency to cry at night, much to the dismay and frustration of many a parent. There are many reasons for why this might be: the baby is hungry, cold, wet, just wants to be held, someone made a noise that woke them up. However, a recent study described in a Science News article provides another reason for why this nighttime crying occurs: it prevents the baby’s mother from getting pregnant again.

Evolutionary biologist David Haig proposes in the past, babies that cried at night had a better chance of survival. This is because the constant interruptions have multiple effects on the mother, many of which act as a kind of birth control. In addition to interrupting potential late-night liaisons and making the mother exhausted, regular nighttime breast-feeding causes hormonal changes in the mother that can delay ovulation (though this is not a foolproof contraception method). Combined, these results of nighttime crying reduce the chances of the mother getting pregnant. How does this relate to the baby’s survival? The answer is simple: if the mother is not devoting resources to another child then the baby will receive more attention and care from the mother during a very vulnerable stage in life. Thus the baby will be more likely to survive its early childhood, and  therefore be more likely to reach reproductive years during which it can pass on its genes to offspring.

While many point out that babies crying at night is caused by a number of other factors, Haig’s proposal provides a new evolutionary significance for the phenomenon. Not only can nighttime crying be seen as sibling rivalry, as the baby is trying to avoid having more siblings for as long as possible, but also shows an example of the battle between sex-linked genes. Male genes tend to cause behaviors that will result in the passing on of genes to the next generation, regardless of the cost to the mother- which explains why male babies have a tendency to cry more at night than females, because there is no guarantee that the mother’s next baby will carry the male’s genes. However, females carry certain genes that tend to make them sleep longer at night as babies, which acts more in the interests of the mother who wants to have more energy to care for her young. Additionally, Haig points out that nighttime feeding is not actually necessary for the baby in our modern day society where most babies have access to adequate nutrients, which supports the idea of nighttime crying being a clever, though unintentional, survival strategy of babies – and also means that moms don’t need to feel too bad if they skip a nighttime feeding session or two.

The Possible Cause of Humans’ Dark Skin

I came across an interesting article called “Odd Cause of Humans’ Dark Skin Proposed”, which states that skin cancer could have directly driven evolution of dark skin in humans. According to the study, people who have albinism, which is an inherited disorder that prevents human from making black or brown pigments, almost die of skin cancer at young ages. The study suggests that the early death of albino people might be the reason why early humans evolved dark skin.

Individuals with white skin are more vulnerable to skin cancer than people with dark skin. For instance, the Skin Cancer Foundation reported that black or brown pigmented skin has a sun protection factor of 13.4, which is relatively higher than that of the white skin (3.4). When hunter-gatherers began to lose their body hair to keep their body temperature cool during their excessive movement for hunting and gathering, they probably had light skin similar to the chimpanzees that has white skin under their fur. However, the article stated that humans evolved to have dark skin about 1.8 million years ago, then evolved light skin again after they migrated to higher latitudes from Africa.

The paper mentioned that skin cancer itself could have driven humans to have dark skin. In addition to the fact that the probability of developing skin cancer is significantly higher for albino people than for people with darker skin, almost all albino people in Africa developed skin cancer at early ages due to high prevalence of outdoor labor. These early cancers in lighter skinned humans lead them to die before reproduction, thus leaving mostly darker skinned individuals to pass on their genes to next generations. Although this idea is still hypothetical, it was interesting to see that cancer can influence human evolution.

Tracing HIV transmission

I think we all understand the idea of how to trace HIV transmission – by sequencing the viral genomes of different strains and looking at differences, we can map the phylogeny of the different strains. In doing so, we can see who infected who. Here’s an article that summarizes this pretty well.

I thought this was pretty cool because when HIV-positive individuals are told about using condoms and how that prevents infection of HIV-negative individuals – but less often do you hear about preventing transmitting another strain to an already HIV-positive individual. The consequence of infecting an already infected individual is introducing, to some extent, a new virus. Depending on viral loads, re-infection might actually change the viral population dynamics and introduce new mutations and phenotypes to the viral landscape in the individual. The primary consequence of this is that re-infection may lead to drug resistance and dramatically affect treatment course.

I didn’t know to what extent this idea of super-infection was known among the population, but this study shows that the possibility is actually very well known. While this all seems pretty logical and understandable,  I can’t help but think about what this means in the realm of public health – How does this affect how health professionals counsel people living with HIV/AIDS (PLWHA)? Should we treat couples together, regardless of HIV status? Should we sequence strains to see where individuals were infected and use that to develop specific prevention strategies?

Hospitals can hurt you?

I remember hearing about something like this before and found it both ironic and slightly disturbing. Some patients who were admitted into hospitals ended up acquiring these infections they did not have when they went in. This happens in about 5% of hospital patients in the U.S. (or around 2 million cases a year). These hospital acquired infections (HAI) kill around 90,000 people a year. This can be quite disturbing since many of us picture hospitals as these clean sanitary places with everyone wearing masks and gloves for protection. These infections are caused by viral, bacterial, and fungal pathogens. The idea here is that hospitals are essentially a gathering place for all of these diseases. There are 3 categories of risk factors for acquiring HAI.

“Iatrogenic risk factors include pathogens that are present on medical personnel hands, invasive procedures (eg, intubation, indwelling vascular lines, urine catheterization), and antibiotic use and prophylaxis. Organizational risk factors include contaminated air-conditioning systems, contaminated water systems, and staffing and physical layout of the facility (eg, nurse-to-patient ratio, open beds close together). Patient risk factors include the severity of illness, underlying immunocompromised state, and length of stay.”

With these people being in so close a proximity to each other, it makes it easier for the pathogens to move around and therefore infect more people quickly. These people will also be exposed to pathogens they may not have gotten if they did not go to the hospital. It’s actually kind of strange really. Hospitals were developed to try to help people as efficiently as possible, but they do have their problems. I’ve helped out at a hospital before and worked on ambulances. They work very hard to make sure everything is as sanitary as possible for both the patients and staff. However, it is still possible for pathogens to get around. I guess it just shows how persistent (and annoying) they can be.


An Evolutionary Perspective: Why Babies Cry

An article I read looked at a study published in Evolution, Medicine and Public Health, proposed an evolutionary reasoning as to why babies cry at night. The research proposed that babies consciously or unconsciously cry to their mother to prevent the birth of a new sibling that would ultimately end up mean competing for resources, and subsequent survival.  Apparently this sort of behavior does have an effect on mothers: nursing a child, especially at night, can stop women for resuming ovulation as essential for reproduction.  In this case, the baby is somehow employing a “survival of the fittest” mentality. Of course, many doctors do not agree, and argue that on the contrary, the nightly breast feeding may be cooperation as both baby and mother may benefit nutritionally and in terms of general health.

I personally jumped to Bonita’s presentation today about possible evolutionary theories behind anxiety, and I think the basis of attachment theory – the attachment a child has for his or her mother – causes anxiety may be the only basis of the child’s crying. It may be an anxiety of an inset fear of being separated from the mother, even if she is nearby that could cause crying fits, and as a child matures that anxiety is quelled with logic and understanding. Otherwise, looking at the theory proposed by the study, I do not see why a baby would EVER stop crying even after it matures into a child or older, at least until 15 or 16. Up to that point, it would still have a certain concern of competing for resources or attention and would not stop crying at night until it no longer was dependent on the mother for resources or survival. Of course, I am not an evolutionary biologist, so the theory might not be as ridiculous as it sounds to me, but I would personally need to see a LOT more research before I believed this one.



The Surprising Reason Babies Cry at Night. (n.d.). Care2. Retrieved April 24, 2014, from http://www.care2.com/greenliving/the-surprising-reason-babies-cry-at-night.htmlcry

How is Darwinian medicine useful?

The article, “How is Darwinian medicine useful?”, written by Randolph M Nesse caught my attention, because it emphasized the usefulness of evolutionary principles in medicine. I think it is appropriate to post a blog about this article, since it is very relevant to our course in understanding evolution in sickness and in human health.

Evolutionary medicine uses an evolutionary perspective to learn why our body is not perfect and why diseases exist in human population. The article lists main principles of Darwinian medicine for explanations to these questions. One of the examples that the paper mentioned is that the obesity and its associated problems arise because our body is not designed to live in the modern environment. Natural selection shaped human appetite regulation mechanism in order to survive the periods of famine based on the environment in the ancient times. Another example the author mentioned is the usefulness of human defense systems. Pain, nausea, cough, fever, vomiting, diarrhea, fatigue, and anxiety are all common defense mechanisms. These are not problems of themselves but it is an attempt to cure a problem. In addition, the paper explores the reason why humans are vulnerable to certain diseases.  One main reason stated is that natural selection is a random process with no direction. Moreover, the purpose for the natural selection is not to make an organism either perfect or healthy, but to maximize reproduction.

The paper emphasizes that the evolutionary view offers a richer view of the human body as a product of natural selection. I agree with this statement, and I believe evolutionary medicine will advance our understanding of the pathogenesis of various diseases. In addition, health professionals will be able to find more effective treatments by understanding why people get the disease rather than by simply considering how they get the disease.

Evolution of Psychology

I posted something about psychology before, but never got into too much detail about it. I did my presentation today about anxiety disorders and we also talked a little bit about personality disorders. During class we talked about the new DSM-V for mental disorders. The development of this book is particularly interesting to me because it shows how time, people, and society changes our views on mental disorders. It was not long ago that homosexuality was diagnosed as a mental disorder and has now been removed. The reason I find this manual so fascinating is because it looks into the cognitive side of medicine and not focussing on biology alone. I know this is a biology class, but mental disorders and psychotherapy fit into medicine as well.

With the new book out, there has been some new changes that have sparked controversy among the field. One of them is the constantly changing criteria for illnesses, new illnesses added or removed, and just things being reorganized. However, this manual does have to evolve has new information is found and societal views change. Like I stated before, homosexuality was classified as an illness and is now removed. Medicine and medical practices have been updated regularly as new information is found so it stands to reason that the DSM change as well.

I suppose one of the biggest issues with mental disorders are they are hard to define and people have different ideas on causes and who has it and who doesn’t. I believe this statement from NIMH director Thomas Insel said it best:

“The weakness is its lack of validity. Unlike our definitions of ischemic heart disease, lymphoma, or AIDS, the DSM diagnoses are based on a consensus about clusters of clinical symptoms, not any objective laboratory measure. In the rest of medicine, this would be equivalent to creating diagnostic systems based on the nature of chest pain or the quality of fever.”

The proposed definitions for psychiatric disorders in the new manual were too broad and ignore smaller disorders that were lumped in with a larger diagnosis. Although one could argue that pinning down a disorder is hard on it’s own. One person may say you have this, but when you go to someone else, then you get a completely different diagnosis. There are few clear cut lines in mental illness, which is why I believe more research needs to be done. While some may think mental illness like depression are just something you can get over, this is not true and to fully understand it means we must learn more about illnesses and maybe improve the DSM to help with diagnosis.