Relationship Between The Different Theories Regarding Menopause In Women

Introduction

Over the past centuries, evolutionary biologists have investigated and explored the enigmatic field of evaluating the theory of why menopause occurs in females. Currently, the two-prevailing branch of menopause theories proposed are categorized as adaptive or non-adaptive hypotheses. The former hypothesis concentrates on selective circumstances which may advance and enhance reproductive senescence as well as the individual’s overall fitness. Contrarily, the latter hypothesis focuses on analyzing the specific conditions of final reproduction related to life expectancy. Menopause is commonly presumed by evolutionary biologists and life history theorists to have emerged early in the process of human evolution; however, proposed theories compiled thus far suggest different mechanisms and reasonings as to how menopause may have developed.

As a result, there has not been a specific hypothesis universally declared to be proven correct, which conveys the notion of how much more remains to be known regarding this subject. Menopause is a natural part of woman’s life cycle; it represents the final stage in which women can reproduce and correspondingly improve her fitness. The array of unpleasant symptoms associated with menopause challenges why this condition has arisen in women primitively and embraces the significant relevance in our lives.

This paper will be addressing three specific hypotheses introduced to clarify menopause existence: the Patriarch Hypothesis, the Game Theory Model, and the Reproductive Conflict Hypothesis by comparing and contrasting each argument as well as assessing how plausible or unreasonable each theory appear. The discussion concerning menopause theories has been a dilemma in evolutionary biology with diverse hypotheses being suggested but no consensus emerging; the priority of learning about why women cease to reproduce at later age should be emphasized due to its extensive impact on human population.

Methods

To assemble data on various menopause theories proposed on media, PubMed, a search engine which allows access to database associated with medicinal, pharmaceutical, and life science articles, was used. Furthermore, the SFU library database was utilized, which primarily resulted in approximately 30 articles to briefly scan and select from. To narrow down the relevant article search, key words such as “menopause theory”, “evolutionary theory”, “life history theory”, “menopause”, “fertility”, “kin selection”, were used in combination to retrieve specific peer-reviewed articles. In addition, following the guidelines provided in the grading rubric, required and recommended articles to read from syllabus were selected in accordance; especially with a focus on lecture three material.

Results

The three hypotheses predominantly discussed in this paper are the Patriarch Hypothesis, the Game Theory Model, and the Reproductive Conflict Hypothesis. First, the Patriarch Hypothesis states that selection favored the extension of life expectancy in males once they obtained a superior position in society and were able to productively reproduce. Menopause is described as a by-product of this effect since the genes responsible for the longevity outcome were not on the Y chromosome. In short, due to female life span being extended in addition to males, menopause occurred as females have a depletion in available oocytes for future reproduction (Marlowe, 2000). The article presents reasonable evidence from hunter-gatherer period and indicates three conditions which must be presumed in order for the Patriarch Hypothesis to be plausible: first, oocyte depletion must be a constraint; second, the genes accountable for the longevity effect must not be on the Y chromosome; and third, some old men must reproduce (Marlowe, 2000).

Second, the Game Theory Model (GTM) is the combination of several main adaptive hypotheses proposed regarding the emergence and maintenance of menopause. In particular, this article lists 10 hypotheses suggested to explain menopause occurrence, including both adaptive and non-adaptive branch. The author declares the primary goal of the study is to assemble five adaptive hypotheses and examine the advantageous or non-advantageous interactions between them (Thouzeau & Raymond, 2017). Nevertheless, due to the inadequacy in two of the selected hypotheses, they concluded that the Maternal Mortality Cost Hypothesis, the Grandmother Hypothesis, and the Trade-Off Between Menopause and Migration Hypothesis would in combination, markedly illustrate the development of menopause. Moreover, the author conveys in situations where older women do not reproduce, menopause is favored, whereas during conditions in which older women do reproduce, menopause is disadvantaged (Thouzeau & Raymond, 2017). The central purpose of the article was to possibly explain the evolution and progress of menopause in combination of the hypotheses stated above (Thouzeau & Raymond, 2017).

Lastly, the Reproductive Conflict Hypothesis (RCH) suggests that the cost of reproductive competition between younger and older generation of females in same community is absent from the calculations of overall fitness equation which may have resulted in menopause (Skjærvø & Røskaft, 2013). The article performs an experiment on Norwegian women and the corresponding results illustrate that both generations appear to encounter forms of fitness benefits amidst co-breeding. More importantly, the author claims that the result of study did not uphold the RCH; there was no evidence to imply that co-breeding had a negative impact on the fitness of younger or older generation of women (Skjærvø & Røskaft, 2013). The article’s most crucial limitation was the lack of data due to exclusively studying two communities and its family structure.

Discussion

The menopause riddle has resulted in numerous scientific articles debating and hypothesizing which designed theory qualifies with justifiable background evidence. The hypotheses mentioned in this paper all suggest different processes as to how menopause has emerged in human evolution. The Patriarch Hypothesis emphasizes the high-status population in male hierarchy and interpret menopause as a by-product of this event as an adaptation. The evidence that the author provides to establish the male-male competition are principally based on ancient Australian society named Hadza, specifically from hunter-gatherer period (Marlowe, 2000). In comparison, the Reproductive Conflict Hypothesis (RCH) also allude to the idea that menopause may be understood in consideration of both aging progress in general as well as our increased lifespan over the years. However, in opposition to the Patriarch Hypothesis, RCH assert that menopause has evolved as an outcome from reproductive competition between generations of women.

As the article disproves this theory by conducting a research which discovered that fitness expense is not apparent in younger nor older generation of women while they co-breed, RCH is not an appropriate theory suggested to prove menopause occurrence (Skjærvø & Røskaft, 2013). The Game Theory Model (GTM) is a combination of three adaptive hypotheses proposed with the fundamental ground that any fitness advantage should be counterbalanced with the palpable disadvantage of ceased reproductive function in women. Examining each hypothesis in detail, the Maternal Mortality Cost Hypothesis suggests that because young offspring are profoundly reliant on care from mother and maternal mortality increases with age, menopause occurs as it can establish maternal care of child by preventing maternal mortality (Thouzeau & Raymond, 2017).

Contrarily, the Grandmother Hypothesis refers to extended post-menopausal life span in female being explained by kin selection (Hawkes & Jones, 2007). In short, grandmothers who contribute to alloparental care to their grandchildren increase their fitness which dismisses the necessity to reproduce. Lastly, the Trade-Off Hypothesis suggests that in female-biased migration society, a gene may be selected for that trades menopause with higher likelihood of marriage (Thouzeau & Raymond, 2017).

All the hypotheses included complement each other as part of adaptative theories; this signifies that the proposed theories should demonstrate why direct reproduction will generate lower overall fitness than investing in substitute options (Kaplan, Gurven, Winking, Hooper, & Stieglitz, 2010). The adaptive hypotheses should formulate the question of: “Why should women cease to reproduce and help descendants, instead of continuing to reproduce with the help of descendants?” (Kaplan et al., p.31). The three hypotheses mentioned frame its theory based on this statement and build up evidence around how the theory answers the question. The various articles explain how each theory could impact human population in the modern world. For instance, one is how insufficient facts are known about maternal reduction and how the process of aging influences costs associated with reproducing which should be inspected in future studies by incorporating these menopause hypotheses (Kaplan et al., 2010).

The practical ramification and significance of menopause theories are extensive as it describes the evolution of menopause and probable treatment response by identifying the route of why it was established. The three adaptive hypotheses stated in this paper have the constitutional idea of figuring out why menopause occurs in relation to how overall fitness of women could be benefitted in compensation. Despite an agreement not being achieved yet and life theorists not knowing for certain the precise reason of menopause, evolutionary biology could be a guide to explaining the importance and its implications for future researches.