1.) What is the “Obstetric Dilemma”? Outline the “problem” and provide details in your description.
The “Obstetric Dilemma” is a hypothesis meant to explain why humans are the only primates who require assistance to avoid complications when giving birth while other primates have an “easier” birth process. The “Obstetric Dilemma” explains that the biological tradeoff of becoming an obligate bipedal hominin lessened the size of the human birth canal while the size of the human skull increased. As humans became obligate bipedal primates the shape of the human pelvis changed dramatically. The pelvis which evolved to allow humans to stand and walk on two feet without waddling, like many of our primate cousins do when walking as a bipedal individual, included repositioning of the pelvis and a more curved basin like pelvis. These changes caused the birth canal to change from an oval shape like most other primates to the more circular shape associated with humans today. The second problem associated with human birth is the size of the infant’s head. Humans have large skulls when compared to our primate cousins and as the birth canal shifted in shape to a circle and became smaller the human head continued to evolve and become larger. As the head became larger there was less and less extra room for a human head to pass through in the birth canal. Primate babies are also born facing forwards while human babies are born facing backwards. When primate babies are born facing forwards this allows for the primate mother to reach down and guide her infant from the birth canal. Human babies are born facing backwards making it difficult for a mother to deliver her child without assistance because of the turning the baby must go through before completely exiting the birth canal.
2.) We’ve discussed how birth can be accomplished alone, but many women choose to give birth with assistance. Discuss why they may need assistance (physically, medically or socially). What properties of birth may necessitate physical or medical assistance?
While our primate cousins give birth alone human women rely on medical and social assistance. Birth is especially heavily medicalized in the western hemisphere. There are many reasons why giving birth has had an increase in medical assistance. As a certified Emergency Medical Technician there are a multitude of situations I was taught to prepare for when faced with a woman in labor. Medical assistance may be needed for premature births, without medical assistance available directly after birth premature infants may not have a chance at life. The human birth canal also presents a challenge for human birth. If a child is presented in a breech position or if a limb presentation occurs the child would not make it out of the birth canal alive. The umbilical cord of human babies and the human birth canal also present issues. If the umbilical cord is wrapped around the infant’s neck or a limb the umbilical cord can cut off oxygen and blood supply resulting in death or amputation of the infant’s limb. Unlike our primate cousins the narrow birth canal of humans also creates problems for the birth of babies with especially wide shoulders. Advanced human medicine and technology allows medical professionals to prepare for high-risk pregnancies or infants with birth defects. Socially women may need assistance because this is a very high stress time. Women may also want social assistance because they are giving birth in front of a room of strangers.
2. Neanderthal & Human Interbreeding:
Several modern human populations have Neanderthal and Denisovan DNA in their genome. This indicates that these species were all interbreeding. Read the PLOSOne article “The date of interbreeding between Neanderthals and Modern Humans” and answer the following questions.
1.) When do the authors think this interbreeding occurred and how did they determine this?
The authors think that interbreeding occurred when modern humans carrying upper Paleolithic technologies encountered Neanderthals as they expanded out of Africa. This was determined by measuring the extent of linkage disequilibrium in genomes of present day Europeans and found that the last gene flow from Neanderthals into Europeans likely occurred 47,000 – 65,000 years ago without including bias from demographic models. With including bias from demographic models the last gene flow may have occurred as recently as 37,000 years ago to as late as 86,000 years ago. To compute this value scientists measured the linkage of disequilibrium after the time of last gene flow between Neanderthals (or their relatives) and human ancestors. Linkage disequilibrium is the sharing of alleles between two or more populations that does not happen due to randomness. In this experiment Neanderthals and European DNA was analyzed for specific patterns and spacing between two linkage disequilibrium, admixture and non-admixture. Two alleles were focused on specifically, one allele that was found on Neanderthal lineage and the other allele that was found in modern human lineage. Allele decay rate was then taken into respect and determined when the allele was introduced into the human lineage and while still remaining in the Neanderthal lineage.
2.) Discuss what they think this means for human evolutionary patterns?
Scientists talked about how the date of 37,000-86,000 years ago was too close to modern humans to be consistent with the “ancient African population scenario”. Instead the results indicate Neanderthals being more closely related to non-Africans than to Africans is due to recent gene flow. The date of gene flow along with archaeological evidence suggests the two populations met somewhere in Western Eurasia, possibly the Middle East. The calculated genetic estimates are too recent to be consistent with the appearance of fossils of modern humans outside of Africa and instead point to gene flow in a more recent period, the modern humans expanded out of Africa carrying modern Paleolithic technologies. The authors also mention the possibility of humans interbreeding with other species, which were genetically similar to Neanderthals.
3.) What do you think about this issue? If interbreeding was possible, are we all the same species (Homo sapiens)?
I do not think that if interbreeding were possible we are all the same species. For example lions and tigers while they can create offspring such as ligers and tigons do not breed or interact in the wild because they are not the same species. Offspring such as ligers and tigons are usually the result of humans forcing breeding upon two felines to create a “designer” feline of sorts. Ligers and tigons produced by this mating are fertile and have the ability to breed with lions and tigers. The reason however ligers and tigons do not become their own hybrid species is because being a hybrid often comes with many health complications. Even though these animals are fertile and have the ability to reproduce they may be outcompeted by their purebred species for this opportunity. The breeding of humans and Neanderthals may have once been similar in nature to the breeding of lions and tigers. Humans and Neanderthals may not have bred unless their population was under extreme circumstances such as death or lack of available mates. The offspring that were produced form Neanderthal and human mating may have like ligers and tigons been able to reproduce but were out competed by their purebred competitors eliminating the possibility of a Neanderthal and Homo sapiens hybrid species. Some of these Homo sapiens and Neanderthal mix offspring did reproduce however it was a very small amount thus only certain humans having 3-4% of Neanderthal DNA. Based on the reasoning provided above I do not think Homo sapiens and Neanderthals are all the same species even though some humans do have some Neanderthal DNA.
Article link http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002947
3. Modern Eugenics:
Although the term “Eugenics” has a negative connotation in the western vernacular, the idea still exists and is visible through programs of genetic and prenatal screening. Check out this piece on PLOSone’s DNA science blog “Genetic Testing for all: Is it Eugenics?” and provide you thoughts to the questions below.
1.) How is Eugenics defined?
Eugenics is defined as the science of improving a human population by controlled breeding in an effort to increase desirable traits and characteristics within the population.
2.) Do you think modern genetic screening tests are related to eugenics? Consider how genetic screenings may help eliminate deadly diseases and how testing may it effect choice if a “non-life threatening” genetic disorder is detected. (For ex. Down syndrome is a genetic variance that may not affect a person’s ability to live a full life.)
I do not think modern genetic screening tests are related to eugenics. As Lewis states at the end of the paper modern genetic screenings are optional. Eugenics is by definition controlled breeding, controlled breeding would mean having only the healthiest humans with few to no genetic markers for disease reproduce. Genetic screenings inform the potential parents of possible genetic problems their child may have but in no way dictate their ability and opportunity to reproduce. BRCA testing looks for mutation in the genes of BRCA 1 and BRCA 2. Mutations raised by these genes can leave someone at a higher susceptibility for some cancers. Being tested for a higher than normal rate of possible cancers does not mean radical surgeries or lifestyles changes are occurring, instead preventative healthcare measures such as sunscreen, exercise, and diet may occur. Cancers are late on-set, treatable and is no reason for a person not to have a child. Fetal DNA testing also known as NIPT is not eugenic because NIPT is not a test for inherited mutations. NIPT tests for trisomies in human chromosomes, which occur by random mutation. This test allows for women of high maternal age or with genetic markers to receive more information and time about possible problems without enduring higher risk procedures such as amniocentesis tests. Therefore the controlled breeding of eugenics would have no effect on this test or influence the people using this genetic markers test because these are random mutations, which happen by chance. The carrier-screening test is a choice that parents can make; it is not forced such as eugenics. Even if the parents are both carriers of a recessive gene and choose not to proceed with in vitro fertilization their freedom to have a child is maintained and not taken away from them was would happen in eugenics.
3.) What about “designer” babies? How may this be affecting evolution, if at all?
“Designer” babies may be affecting the phenotypic traits in evolution. If parents think that tall, thin, blond haired, blue-eyed people are the most physically attractive appearance then less variations of human appearance may occur. If along with phenotypic traits parents and geneticists are designing children who have genetic advantages over non-designer babies this may affect evolution. Children who are healthier, stronger, have better immunity, and are smarter may also create “super mutations” or extreme diseases that are in a sense similar to those we have seen from overuse of antibiotics. With overuse of antibiotics “superbugs” have been created and do not respond to antibiotic treatment. If children are created to have better immune systems we may see “super diseases” such as mumps or chicken pox which could be deadly for non-genetically designed people.
4. Modern Human Variation:
Racial categories are NOT supported by genetics, but the effects of bias and discrimination can have biological consequences. Stress from racial discrimination has been linked to early birth in African American women, higher rates of several diseases and mental disorders, and overall lower life expectancies.
1.) Read the article “More than Skin Deep” and provide a brief synopsis.
The article “More than skin deep” describes the negative mental and physical health effects of racism and racial discrimination in minorities. This leads to perpetual health problems in minorities and health inequalities between minority groups. The experience of discrimination and social exclusion due to racial discrimination thus provokes a stress response in humans and detrimental health effects. Ethnic minority groups suffer from lower life expectancy, a lower access to health services and a higher burden of disease. There is an increasing negative effect on physical and general well being from adolescence to adulthood indicating the detrimental health effects increases over time. Even after controlling for health problems such as exercise, no smoking, and diet ethnic groups had higher chronic cardiovascular, inflammatory and metabolic risk factors. Various minority groups also seem to have higher rates of mental illness including schizophrenia, mood and anxiety disorders and psychological stress. There have been many analyses identifying strong associations between racial discriminations and poor mental health in adults. The risk of health problems seems more prevalent in adults due to minority status and discrimination increasing with age and the risk appears higher in post-migratory environments compared to the country of origin suggesting environmental contribution to health inequalities. When discrimination is perceived as stressful many negative emotional and psychological responses may occur. A physiological response involves the release of cortisol, the main systemic hormonal stress response, which includes numerous metabolic changes and behavioral alterations. Stress also activates the sympathetic-adrenal-medullary axis leading to increased heart rate, blood pressure, vasoconstriction, and overall chronic stress. Studies have proven discrimination has chronic negative effects for health in minorities everywhere, leading to a cycle of lower rates of accessible healthcare, higher perpetual health problems, and higher rates of mortality.
2.) What are the main hormones effecting mental/physical health and how are they operating?
The main hormones, which effect physical health, are cortisol and hormones effecting mental health are dopamine. Cortisol effect studies have shown inconsistent results and depend on many compounding factors but it is known that cortisol is a potential hormone when associated with racial discrimination affects overall health. Cortisol is a hormone that helps the body return to normal following a trauma. Cortisol is the main systemic hormonal endpoint of the stress response and has numerous effects on the body and the brain including metabolic changes, the immune system, and behavioral alterations. Stress indicated by lower cortisol levels in salivary and serum samples increased heart rate, vasoconstriction, and blood pressure. There is evidence that people who experience chronic social exclusion leads to a greater release of dopamine similar to the levels of dopamine release found in individuals with schizophrenia. This release of greater then normal dopamine neurons projected into the prefrontal cortex and the anterior cingulate cortex could be contributing to abnormal activation and connectivity and the presence of schizophrenia, mood and anxiety disorders in minorities.
3.) What effect can this have on human population genetics? Consider how epigenetic studies have shown that trauma (physical and mental) can have effects through multiple generations.
The effect this could have on the human population genetics means that minorities may be more susceptible to disease and illnesses. Minorities are currently caught in a perpetual cycle of increased health risks even when diet, exercise and smoking were controlled, lack of available and affordable health care, and early death. In an article published online Holocaust survivors passed on altered stress hormone production of cortisol onto their offspring possibly leaving them more susceptible to anxiety disorders. In people with Post-Traumatic Stress Disorder their offspring also had lower than normal cortisol levels present. This could mean the offspring of minorities may chemically resemble the offspring of Holocaust survivors and PTSD individuals leaving their children more susceptible to the risks of chronic stress such as habitual medical problems as well as possible mental illnesses. Minorities are already lacking access to quality healthcare in uptick in diseases as the result of chronic stress and low cortisol levels may have grave consequences on the overall health and reproduction of minority populations.