Modern Human Female’s Ovarian Function Continues to Conceptualize on Natural Selection, Adaptation and Variation as Earlier Primates (2013)

The concepts of variation, adaptation, mutation and natural selection are encompassing or intersecting throughout the historical study of human origins and evolutionary structures.  Bipedal adaptations by Australopithecus assisted in the morphological flexibility of the pelvis, as well as, in the efficiencies of acquiring different foods.  Differentiating the morphology and behavior between Homo Erectus, anatomically modern humans or Eurasia’s Neanderthal factors into the complexities of genetic variations and environmental constraints.  The reliance on clines to detail one’s physical and genetic traits per environment as opposed to superficial constructs such as “biological race” accounts for  the intricacies of the many variable traits that doesn’t falls into neat classifications.  In the context of genetic and environmental variation and reproduction ecology, modern human may have different dynamics with regards to their availability of resources, ecological settings, physiological function or behavior than from earlier primates in the Old World; however, the historical narrative of continuous variation still applies.  In this respect, I suggest that the modern, human, female ovarian function continues to conceptualize on natural selection, adaptation and variation within the negotiation of available resources and local environments as earlier primates.  Internal negotiations of reproductive function are a continuous evolutionary success from earlier primates.  In the rest of this analysis, I will present two different and/or complementing theoretical models of human ovarian adaptation: Flexible Stress Response Model (FRM) and Developmental Energetics Model.  Reviewing these particular models of human reproductive ecology would assist me in thinking in parallel terms of the ecological, physiological and behavioral conditions of earlier reproduction by primates. 

One bio-anthropologist that I consider in this review is Virginia J. Vitzthum (2013), who negated her original hypothesis that women living in the high-altitude, low-oxygen settings of the Andes, Bolivia suffered from low fecundity due to hypoxia.  On the contrary, her data reflected that Bolivian women born in the high regions were actually physically acclimated to the environmental conditions compared to the women living in the lowland areas.  While the ovarian function still appears to be a very complex study with many remaining questions, Vitzthun (2013) postulates that the difference between the women in both highlands and lowlands has less to do with low or high fecundity but more to do with the genetic or environmental adaptations and multiplex responses from the endocrinology system.  In this regards, every female – within and between populations – has an internal system that responds differently due to genetic attributes and/or along with the confluence of environment factors (Harris and Vitzthun: 2013:213-234, Vitzthun: 2009:95-106).  Using supporting data from her study, Vitzthun (2013: 208-218; 2009:101-124) theorizes on a Flexible Response Model (FRM) that suggests women’s reproductive fitness is based on an assessment of their existing conditions (i.e. accessibility to resources, environmental stressors or physiological behavior, etc.) compared to prior conditions or a baseline mark of their history; likely prior to maturity. If her current status is equal or greater than her baseline, then natural selection would likely find it as her most optimal solution for reproductive investment.  However, if a female’s reproductive fitness status is assumed to be in worse conditions than her baseline or that she’s likely experiencing temporary, arduous circumstances, then her reproductive fitness is likely to be low or unresponsive until things improve or she becomes acclimated to these conditions.  In brief, Vitzthum’s reproductive model underlies how variation of a woman’s life history experience, endocrinology and ecological constraints negotiates with one another to seek the most optimal solution in reproductive ecology for fitness. 

Anthropologist Peter Ellison (2008) also considers that women’s fecundity, ovarian variability and adaptation is too variable to be measured by a particular standard within and between populations.   His Developmental Energetics model is based on energy availability and demand.  Ovarian function is also impacted by a woman’s energy intake versus the demands required to maintain or accrue reproductive investment.  Should a woman endure energy-depleting conditions, then trigger responses are sent to her steroid levels for regulation.  Her body undergoes a reproductive adaptation strategy to determine the best possible solution for reproductive fitness.  Ellison’s work has been criticized particularly by Vitzthun (1997:242-258, 2009:115-123) given that his model has not accounted for the variances of reproductive fitness between populations.  The data that showed women in low-resource areas had higher fertility rates than women in industrialized areas was unexplainable in the energetics model.  Ellison (2008:183-184) reconciled the criticism by suggesting that women in industrialized nations have better access to artificial birth control methods than women in low-resourced areas.  In the most updated article, “Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning” (2013) Harris and Vitzthum has since implemented energetics into her theory.

In this analysis, I reviewed how primate evolutionary concepts of variation, adaptation and natural selection are relative to the ovarian function of modern human females by utilizing two different anthropology models that factors reproductive fitness on the basis of reproductive negotiations and strategies of available resources.   In conclusion, modern humans continue to seek the most efficient solutions for survival and reproductive fitness, just as their earlier ancestors.

References

Ellison, Peter
2008 Energetics, Reproductive Ecology, and Human Evolution. Paleo Anthropology: 172- 200

Harris, Amy L., and Virginia J. Vitzthum
2013 Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning. Journal of Sex Research 50(3-4):207-246.

Vitzthum, Virginia J.
1997 Flexibility and Paradox: The Nature of Adaptation in Human Reproduction. The Evolving Female: A Life History Perspective:242-258.

Vitzthum, Virginia J.
2008 Evolutionary Models of Women's Reproductive Functioning. Annual Review of Anthropology 37(1):53-73

Vitzthum, Virginia J.
2009 The Ecology and Evolutionary Endocrinology of Reproduction in the Human Female. American Journal of Physical Anthropology 140(S49):95-136. 

Vitzthum, Virginia J.
2013 Fifty Fertile Years: Anthropologists' Studies of Reproduction in High Altitude Natives. American Journal of Human Biology 25:179–189