HSCI 216 Lecture 7: HSCI 216 Lecture 7

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HSCI 216
Day 7
June 29, 17
Human Reproductive Ecology II
Learning Objectives
- To be able to explain and distinguish between the pathology and adaptionist paradigm,
and how they explain the low live births to menstrual cycle ratio
- To explain how energy may be a modulator of reproduction to describe
- To describe the effect of seasons on human reproduction
- To explain how stress can suppress reproduction
What could explain the low rate of live births to menstrual cycles?
2 paradigms have evolved to explain this ratio
- Pathology paradigm
- Adaptionist paradigm
“Pathology” Paradigm
- “Human reproduction entails a fundamental paradox: although it is critical to the survival
of the species, the process is relatively inefficient
- Refer to reproductive losses such as miscarriages and stillbirths are referred to
o Reproductive pathologies
o Reproductive failures
- Suggests female reproductive physiology is broken by design
“Adaptationist” Paradigms
Reproductive losses Reproductive failures
Suppression mechanism
Regulate timing of reproductive events
- Not all conditions are suitable for investment in reproduction
- The ability to interrupt reproduction can provide a selective advantage
What is the purpose of preventing reproduction during inauspicious times?
- By avoiding during this time, it allows females to focus their resources on:
o Their own survival during these inauspicious times
o Helping already existing offspring survive
o Avoids investing in offspring with reduced fitness prospects
o To improve their overall condition to invest in future offspring once conditions
improve
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- What are the mediating mechanisms behind preventing reproduction during inauspicious
times
Hypothesis: Energy is the ultimate modulator reproductive function
- Peter Ellison
The ecological context of human reproduction
- Social Environment
o Cultural norms
o Subsistence activities
o Regional political changes
- Physical Environment
o Climate
o Altitude
o Availability of resources
o Local disease burden
- Constitutional
o Genetic factors
Energy Availability Reproductive function
- All these can influence each other
At which point could reproduction be prevented?
1. Pre-conception Behaviour
a. Avoiding intercourse
2. Anorgasmy Male End
a. No orgasm no sperm delivered to female reproductive tract
3. Anovulation Stress?
a. No ovulation = no egg = no egg to be fertilized
4. Miscarriage
a. No implantation/ implantation in wrong place
b. No viable pregnancy
5. Post-conception behaviour
a. What a mother does during pregnancy
The Menstrual Cycle
- Estrogen and progesterone increase after ovulation
o Needed to thicken endometrium
o Need for successful implantation (appropriate levels)
- Implantation should occur between days 8 to 10 of gustation to have high chance of
success
- Low progesterone degenerative endometrium
- Due to high stress level, therefore stress affects implantation
Proximate explanation for variation in female fecundity
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Some important terms regarding energetics
Energy status:
- Stored energy
Energy balance:
- Energy intake energy expenditure
Energy flux
- Energy turnover (turned what has been stored (fat) into energy)
The effects of seasons in humans
- Grazyna Jasienska
- Looking at a population of Polish farm women
Energetic challenges can affect the chances of successful conception
How do energetic challenges differ between women in industrial vs developing countries?
- Industrial countries (Canada and US)
o Extreme dieting
o Strenuous exercise
- Developing countries
o Low calories diet
o Workload in women
- If energy gains + energy expenditure affect reproduction today, then it should have done
so in past
o Season can be a very good predictor of energy availability + expenditure
This information inspired anthropologists to ponder about the origin of that association
Back to the population of Polish farm women…
Women involved in agricultural work
- Summer haying and harvesting (women)
- Fall and Winter no agricultural work for women
o Pickling, preserving, cooking, sewing etc.
- Energy expenditure in summer exceeds mean energy expenditure in winter by 37%
- Summer lower progesterone levels than winter: indicates ovarian suppression
- Progesterone is being converted to cortisol
Energy expenditure as a modulator of reproductive function
Did variables describing nutritional status and energy balance correlate with progesterone levels?
No
- Body weight, body fat or changes in either = no correlation with progesterone levels
Energy expenditure was the only variable responsible for suppressed progesterone levels during
the summer work-related
What happens when energy balance is positive?
Is it really all about energy?
The evolution of origins of obstetrics:
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Document Summary

To be able to explain and distinguish between the pathology and adaptionist paradigm, and how they explain the low live births to menstrual cycle ratio. To explain how energy may be a modulator of reproduction to describe. To describe the effect of seasons on human reproduction. To explain how stress can suppress reproduction. 2 paradigms have evolved to explain this ratio. Human reproduction entails a fundamental paradox: although it is critical to the survival of the species, the process is relatively inefficient . Refer to reproductive losses such as miscarriages and stillbirths are referred to: reproductive pathologies, reproductive failures. Suggests female reproductive physiology is broken by design. Not all conditions are suitable for investment in reproduction. What are the mediating mechanisms behind preventing reproduction during inauspicious times. Hypothesis: energy is the ultimate modulator reproductive function. Social environment: cultural norms, subsistence activities, regional political changes. Physical environment: climate, altitude, availability of resources, local disease burden.

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