Lecture 8 Flashcards
Pathology Paradigm
Views reproductive issues primarily through the lens of disease and dysfunction.
Focuses on what goes wrong in the reproductive process rather than considering the inherent inefficiencies and complexities of human reproduction as a natural phenomenon.
An alternative view to the pathology paradigm - adaptationist paradigm
Adaptationists paradigm:
- reproductive losses DOES NOT equal to reproductive failures
- suppressions mechanisms –> regulate timing of reproductive events
The ability to interrupt reproduction can provide a selective advantage
Preventing reproduction during inauspicious times is hypothesised to allow females to focus resources on:
- surviving the inauspicious times
- helping already existing offspring to survive
- avoid investing in offspring with reduced fitness prospects
- improving overall condition to invest in future offspring
So what could the mediating mechanisms be for reproductive function?
Energy as the ultimate modulator of reproductive function
In this context, it implies that energy levels can affect various reproductive processes, such as the timing of reproduction, fertility rates, and overall reproductive success. Therefore, the answer to the question about mediating mechanisms is indeed pointing towards energy as a fundamental factor that modulates reproductive function. This highlights the importance of energy in determining how and when reproductive activities occur, especially in response to environmental and physiological conditions.
“mediating mechanisms” refer to the processes or factors that influence the relationship between underlying conditions (such as energy availability, social support, or health status) and reproductive outcomes (like fertility, timing of reproduction, and success of offspring).
The ecological context of human reproduction (social and physical environment)
Social environment:
- cultural norms
- subsistence activities
- regional political changes
Physical environment:
- climate
- altitude
- availability of resources
- local disease burden
Both physical and social factors related to one another, and relate to constitutional genetic factors which then lead to: energy availability leading to reproductive function
the probability of conceiving, delivering and raising a child can be reduced at different stages
- pre-conception behaviour (coitus avoidance)
- anovulation (absence of ovulation, ovaries are not releasing eggs regularly or at all - irregular or no period)
- miscarriage
- post-conception behaviour (neglect, abandonment and infanticide)
Reproduction can be avoided at different stages
- anovulation
- miscarriage
Understand the menstrual cycle!!
Proximate explanation for variations in female fecundity: what does fat storage, energy balance, ovarian function, cortisol, and insulin independently influence?
FAT STORAGE:
This refers to the amount of body fat that is stored in adipose tissue. Body fat is essential for energy storage and plays a role in hormone production
ENERGY BALANCE:
Energy balance is the equilibrium between the calories consumed through food and beverages and the calories expended through physical activity and metabolic processes. A positive energy balance (more intake than expenditure) can lead to weight gain, while a negative balance can lead to weight loss.
OVARIAN FUNCTION:
Ovarian function encompasses the processes involved in the development and release of eggs (ovulation) and the production of hormones such as estrogen and progesterone. Proper ovarian function is crucial for regular menstrual cycles and fertility.
CORTISOL:
Cortisol is a steroid hormone released by the adrenal glands in response to stress. It has various effects on metabolism and can influence reproductive hormones. Elevated cortisol levels can disrupt normal ovarian function.
INSULIN:
Insulin is a hormone that regulates blood sugar levels and plays a significant role in energy metabolism. It is produced by the pancreas and helps cells absorb glucose for energy. Insulin also has implications for fat storage and can affect ovarian function, particularly in conditions like insulin resistance.
Proximate explanation for variations in female fecundity: How does fat storage, energy balance, ovarian function, cortisol, and insulin relate to one another?
Cortisol and Insulin: High levels of cortisol can lead to insulin resistance, which can affect energy balance and fat storage.
Fat Storage and Energy Balance: The amount of fat stored in the body can influence energy balance. Excess body fat can lead to hormonal imbalances that affect ovarian function.
Ovarian Function and Hormonal Regulation: Proper ovarian function is dependent on a balanced energy status and appropriate levels of hormones like insulin and cortisol. Disruptions in any of these areas can lead to reproductive issues.
Imbalances in any of these factors can lead to complications such as anovulation or infertility.
Energetics
Energy status (stored energy)
Energy balance (intake - expenditure)
Energy flux (energy turnover)
energetic challenges can affect the chances of conceiving a pregnancy
Extreme dietary restrictions and strenuous exercise are often associated with ovarian suppression in women from industrial countries and developing countries
- what could be the ultimate explanation of that association?
- how would you test your hypotheses?
What factor is a good predictor of energy availability and expenditures?
Seasons!
If energy gains and engird expenditure are today affecting reproductive function, then they should have done so in the past
Energy flow in women involved in agricultural work
- no energetic (food) restrictions across the year
- fall and winter months characterised by low physical (energetic) demands (no agricultural work)
- harvest and haying performed during summer
- energy expenditure was 37% higher during the summer than during winter
energy expenditure and ovarian function (argicultural women study)
- progesterone levels were lower during summer than in winter, suggesting ovarian suppression in the summer (found that this is due to work related energy expenditure)
Progesterone is a hormone produced by the ovaries after ovulation and is essential for preparing the uterine lining for potential implantation of a fertilized egg. It plays a critical role in maintaining pregnancy.
energy expenditure as a modulator of reproductive function (progesterone levels)
- nutritional status and energy balance (evaluated via body weight, body fat) did not correlate significantly with progesterone levels
- energy expenditure (work-related) did. It was the only variable linked to the lower progesterone levels observed during summer
How easy is it for women to give birth by themselves, like most other mammalian females do?
- positive selection for bipedalism ultimately led to changes in the way females gave birth
- Bipedalism refers to the ability to walk on two legs
- Positive selection refers to the evolutionary process where certain traits become more common in a population because they confer some advantage for survival or reproduction.
- The transition to bipedalism had significant implications for the anatomy of the pelvis. As hominids adapted to walking upright, the shape of the pelvis changed to accommodate bipedal locomotion. This change affected the birth canal, making it narrower and altering the mechanics of childbirth.
- Consequently, the process of giving birth became more complex. The evolution of bipedalism may have led to a situation where human infants are born at a relatively earlier stage of development compared to other primates.
- This is often referred to as “neoteny,” where offspring are born in a more immature state, requiring extended care and nurturing.
- Evolutionary Trade-offs: The changes in pelvic structure due to bipedalism represent an evolutionary trade-off. While bipedalism provided various advantages, it also made childbirth more challenging, leading to increased risks for both mothers and infants during delivery.
Birthing process in quadrupeds (animals that walk on 4 limbs)
In quadrupeds entrance and exit of birth canals are oriented front-to-back (sagittaly)
- The birth canal is the passage through which offspring are delivered during birth. In quadrupeds, the entrance (the part of the canal where the fetus enters) and the exit (the part where the fetus exits) of the birth canal are oriented in a front-to-back direction, also known as sagittal orientation.
- This sagittal orientation means that the canal runs parallel to the body’s midline, allowing for a more straightforward passage for the fetus during delivery. The alignment facilitates the birthing process, as the fetus can move through the canal in a linear fashion. (humans don’t have it linear because of evolution, humans have a more twisted and angled birth canal)
Implications:
Ease of Birth: The sagittal orientation in quadrupeds generally allows for easier and less complicated births compared to the challenges faced by bipedal species, where the shape of the pelvis and birth canal can complicate the delivery process.
Birthing process in primates
The process is similar in primates (similar with humans)
- Primates are a diverse order of mammals that share certain anatomical and behavioral traits. This group includes lemurs, tarsiers, monkeys, apes, and humans
- In non-human primates, the birthing process may also involve challenges related to the size and shape of the birth canal, although the specific adaptations can vary among different primate species.
Birthing process in humans
- birth canal is twisted in the middle (refers to the shape of the pelvic cavity, which is not a straight passage but rather has curves and angles that can complicate the birthing process)
- the inlet (the entrance of the birth canal) is broadest in the transverse dimension (meaning it is wider from side to side), and the outlet (the exit of the birth canal) in the sagittal (front-to-back)
- This difference in dimensions means that the maximum widths of the entrance and exit of the birth canal are perpendicular to each other. This anatomical feature can create challenges during childbirth, as the baby must navigate through these varying dimensions.
- human infant’s large heads are largest in the sagittal dimension (meaning that the measurement from front to back (sagittal plane) is greater than the measurement across the width (coronal plane)), but shoulders are broader in the coronal dimension (side-to-side width)
- the pelvic’s inlet and outlet planes are also perpendicular: this means that the widest part of the inlet is oriented differently than the widest part of the outlet.
Because of this shape, during birth, head and shoulder rotations (of the baby) are required!
What would be the risks for human babies if their mothers adhere to a standard primate birthing process?
In primates, particularly non-human primates, birthing typically involves behaviors that are adapted to their physical abilities. These behaviors include using gravity to aid in the delivery, as well as relying on the mother’s ability to reach and handle her baby immediately after birth. Human babies, however, have larger heads relative to their body size, which can make delivery more complex and risky if it were to follow the standard primate birthing process.
Potential risks include obstructed labor, increased pressure on both the mother and the baby, and a higher likelihood of injury.
Additionally, human neonates (newborns) are born with less immediate physical self-sufficiency compared to many other primates. This means that they require immediate and careful handling after birth, often involving skilled medical assistance to ensure proper breathing and other vital functions. Given these differences, adhering to a birthing process like that of non-human primates could exacerbate these challenges, increasing the chances of complications such as prolonged labor, birth trauma, or respiratory issues in human babies.
Human babies tend to be born facing “backwards”
- this has been argued to increase to risk of harming the baby when mothers, giving birth alone, reach to grab them in helping the process, particularly in the case of a complicated birth
- it also affects her ability to clear the breathing passageway for the infant and, if necessary remove the cord from around the neck
Unattended births are usually associated with higher mortality than attended ones
Can women give birth by themselves?
YES but it is riskier than in other mammals
Trevathan and others argue that said risk led to human birth becoming a social enterprise (this means that childbirth is not just a biological event but also a social one that involves the support of family, community, and healthcare systems)
From midwives to institutionalised birth: In clinical settings there is an increased risk for?
- use of drugs to speed up process
- use of metal monitoring
- posture for labor and delivery
- concern with contamination
- episiotomy (surgical procedure that cuts the perineum, which is the area between the vaginal opening and the anus, during childbirth)
- C-section
AND, critically important: change in the social environment surrounding birth (This implies a transformation from a more personal and intimate setting to one that is more controlled and procedural. Such shifts can have profound implications for the birthing experience, affecting both the mother and the baby’s immediate and long-term health outcomes such as: increased pain, longer recovery times, and a higher risk of infections for the mother, use of instruments (like forceps or vacuum extraction) can increase the risk of physical trauma to the baby & Babies born by C-section may have higher risk of respiratory problems, as they do not experience the same compression of the chest that occurs during vaginal delivery, which helps clear fluid from the lungs)
Evolutionary obstetrics - what is it? Interventions?
Examines how the evolved needs of women during labor may not align perfectly with modern medical practices.
Evolutionary medicine suggests that human childbirth evolved under specific conditions that are different from today’s hospital settings. For example, labor and delivery traditionally involved more community support and natural birthing positions, which may not always be the focus in contemporary clinical environments.
Interventions (to better align with our evolutionary adaptations):
Work with a midwife: primary care during pregnancy, labour, birth, and immediate postpartum period
Add a doula: emotional and practical support and reassurance, natural birthing positions, help with bonding between mother, father, and baby
Effects of social and emotional support in childbirth by midwives and doulas
Midwives and doulas provide emotional and social support through:
- more positive feelings: higher self-esteem and lower postpartum depression scores
- better obstetric outcomes (reduced c-section rates, use of forceps, length of labor)
- increased breastfeeding rates
what is required for successful reproduction?
- energy
- social support
- logistic support
- appropriate health status
- economic resources
what happens when the requirements for successful reproduction is not met?
Health complications:
- maternal: Insufficient energy and poor health status can lead to complications during pregnancy and childbirth, such as gestational diabetes, or increased risk of cesarean delivery.
- Fetal: Lack of proper nutrition and health care can result in fetal growth restrictions, low birth weight, and developmental delays.
Increased stress:
- A lack of social support can lead to increased stress and anxiety for the mother, which can negatively affect both maternal and fetal health. Chronic stress is associated with adverse pregnancy outcomes, including preterm birth.
- Isolation: leading to postpartum depression
Economic strain:
- financial burden
- inability to provide
The ability to interrupt reproduction can provide a selective advantage, how?
Resource Allocation:
- Focus on Survival: When environmental conditions are harsh or resources are scarce, interrupting reproduction allows one to conserve energy and focus on their own survival. This is crucial for maintaining health and well-being during challenging times.
- Investment in Existing Offspring: By delaying or interrupting reproduction, parents can allocate more resources to the care and survival of existing offspring. This increases the likelihood that those offspring will survive to maturity and reproduce themselves.
Improved Offspring Quality:
- Timing for Optimal Conditions: Interrupting reproduction allows individuals to time their reproductive events for more favorable conditions. For example, waiting for better food availability or more stable environmental conditions can lead to healthier offspring with better survival prospects.
- Avoiding Low Fitness Offspring: Reproducing during inauspicious (unfavourable) times may result in offspring with lower fitness prospects. By delaying reproduction, parents can ensure that they invest in offspring that are more likely to thrive.
How does the body identify inauspicious times for reproduction?
Through a physiologic alarm triggered by the effect of those inauspicious times or the anxiety generated by future inauspicious times
STRESS!!!
What is real life stress?
The combination of all daily stressors faced by individuals in the course of their lives
Stress and female reproduction (what + what = what?)
experimental stress + specific stressors = real life stress
What kind of stressors lead to increased levels of cortisol (high stress)
energetic stressors
psychosocial stressors
health stressors
All lead to high levels of cortisol but also high levels of one stress, lead to high levels of other stressors
Increased cortisol during the placentation period (first 3 gestational weeks) is associated with pregnancy loss
True, this period involves placentation, which is when the placenta begins to form and establish a connection between the mother and the developing embryo. The concept highlights that maternal stress during this early stage can significantly impact fetal development, making it a crucial time for ensuring both physical and emotional well-being.
A theory proposed by David Haig, known as the “Maternal–Fetal conflict hypothesis,” which suggests that there is an evolutionary tension between the needs of the mother and the demands of the fetus during the critical time of placentation
Placentation
- before placentation, ovarian steroids produced by the corpus luteum (CL - maternal origin) are crucial for the maintenance of pregnancy
- 3 weeks after conception, the placenta matures and embryonic tissue begins to replace the CL as the main source of steroids
Thus, maternal stress-triggered abortive mechanisms (loss of baby naturally like imbalance of hormones due to increased stress) might be most effective before the placenta matures (gestational week 3)
- maternal energetic investment and the risks associated with pregnancy increase dramatically after placentation
- in other words, the first 3 weeks of gestation might be the last window of opportunity in which a woman’s body can interrupt a pregnancy relatively easily and “cheaply”
Increased cortisol impacts what?
It reduces the mid-luteal progesterone (hormone needed for pregnancy) which in turn impacts implantation and pregnancy maintenance (negatively)
Menstrual Cycle: Findings and Significance
Findings:
- increased cortisol levels predicted untimely increases in progesterone during the follicular phase
- increased cortisol levels predicted untimely increases in the gonadotrophin (LH and FSH) both during the follicular and luteal phases
Significance:
- high follicular progesterone levels have been associated with reduced chances of conception
- untimely increases in gonadotrophin (LH and FSH) negatively affect the ovulatory and luteinisation processes
- reduced levels of ovarian progesterone at midluteal reduce the chances of successful implantation
Understanding when progesterone is high and low for reproduction
Role of Progesterone in Pregnancy
- Essential for Maintenance: Progesterone is crucial for maintaining pregnancy once conception has occurred. It helps prepare the uterine lining for implantation, prevents uterine contractions, and promotes a suitable environment for the developing embryo.
Timing of Progesterone Levels:
- Follicular Phase: (before ovulation), progesterone is low and, estrogen levels are high. If progesterone levels are abnormally high during this phase, it can indicate hormonal imbalances that may disrupt normal ovulation and reduce the chances of conception.
- Luteal Phase: After ovulation, progesterone levels rise significantly to support a potential pregnancy. If conception occurs, these levels need to remain elevated to sustain the pregnancy.
Summary
- increase in cortisol levels were associated with “deleterious” (harmful/negative impact) changes in the profiles of FSH, LH, estrogen and progesterone
- within the first 21 days after conception, high cortisol levels were associated with a higher risk of spontaneous abortion
- real-life stressors associated with reproductive suppression in women
- HPA (hypothalamic-pituitary-adrenal) activation, often in response to stress, can interfere with critical reproductive processes such as follicular development, luteinization, and maintaining a pregnancy. This suggests that the body’s stress-response system can negatively influence reproductive functions.
What is plasticity?
Plasticity refers to the ability of an organism to change its phenotype in response to environmental conditions
What is phenotype plasticity?
This is the capacity of a single genotype to produce different phenotypes in response to varying environmental conditions.
For example, a plant may grow taller in response to increased sunlight or develop thicker leaves in response to drought conditions.
What is developmental plasticity
This refers to changes that occur during the development of an organism, often as a result of environmental factors experienced during critical periods of growth.
For instance, certain animals may develop different physical traits based on the presence of predators or the availability of resources during their early life stages.
