EC Gynaecology

The evolution of the human brain was critical in the expression of basic reproductive strategies and permitted the transition of reflexive estrous cycles to our present social-sexual menstrual cycle. An inventory of the reproductive strategies of our progenitor female mammals provides clues to help explain the causal pathway of menopausal symptoms of today. Such an inventory of progressive adaptations reveals the conservation of key endocrine mechanisms that were modified and seldom abandoned. Evolving to fill emerging environmental niches, ancient mammals adapted hormones they inherited from fish and reptiles to construct increasingly complex breeding systems which led to reproductive isolation resulting in new species. Each new species retained similar basic endocrine foundation but profoundly different controls for breeding. The neural peptide, gonadotropin hormone releasing hormone (GnRH), is the most fundamental hormone in the control of reproduction and changed little in control, composition and structure from fish to mammals. This neural signal acts directly on the limbic system to invoke autonomic reflexes through episodic pulses of secretion. Progesterone is also a consistent and critical control factor across mammalian evolution and acts through feedback loops to modulating GnRH. The evolution of a larger more complex brain aided by the development of placental hormones and more complex adrenals, gradually converted a reflexive estrous mating strategy to a strategy with social-sexual contexts. Environmental cues were incorporated into the neural control of breeding seasons and more complex social systems limited fecundity. Primates replaced most of the reflexive physiology and behavior using progesterone to modulate the neural control centers. Cyclic, prolong hiatuses in progesterone production in higher primates led to the acquisition of mate choice in females and a social-sexual reproductive strategy. Progesterone domination can act to dampen the pulse frequency/amplitude of GnRH secretion and suppresses the reflexes of early reproductive strategies. Lower progesterone may lead to conflicts between higher control and relic reflexes leading to unnecessary and unwanted autonomic responses.

 Keywords: Evolution; Reproductive Strategies; Gonadotropin Hormone Releasing Hormone; Progesterone; Estrus

1. Shideler SE., et al. “Ovarian-pituitary hormone interactions during the perimenopause”. Maturitas4 (1989): 331-339.
2. Lasley BL., et al. “The effects of estrogen and progesterone on the functional capacity of the gonadotrophs”. The Journal of Clinical Endocrinology and Metabolism 5 (1975): 820-826.
3. Gilardi KV., et al. “Characterization of the onset of menopause in the rhesus macaque”. Biology of Reproduction 2 (1997): 335-340.
4. Wise PM., et al. “Menopause: the aging of multiple pacemakers”. Science5271 (1996): 67-70.
5. Lederman MA., et al. “Age-related LH surge dysfunction correlates with reduced responsiveness of hypothalamic anteroventral periventricular nucleus kisspeptin neurons to estradiol positive feedback in middle-aged rats”. Neuropharmacology 1 (2010): 314-320.
6. McConnell DS., et al. “Lowered progesterone metabolite excretion and a variable LH excretion pattern are associated with vasomotor symptoms but not negative mood in the early perimenopausal transition: Study of Women's Health Across the Nation”. Maturitas 147 (2021): 26-33.
7. Padilla SL., et al. “A Neural Circuit Underlying the Generation of Hot Flushes”. Cell Reports2 (2018): 271-277.
8. Szeliga A., et al. “The role of kisspeptin/neurokinin B/dynorphin neurons in pathomechanism of vasomotor symptoms in postmenopausal women: from physiology to potential therapeutic applications”. Gynecological Endocrinology11 (2018): 913-919.
9. Wade N. “Guillemin and schally: the three-lap race to Stockholm”. Science 4340 (1978): 411-415.
10. Phillips JA., et al. “Exogenous GnRH overrides the endogenous annual reproductive rhythm in green iguanas, Iguana iguana”. Journal of Experimental Zoology 2 (1985): 227-236.
11. Yen SS., et al. “The operating characteristics of the hypothalamic-pituitary system during the menstrual cycle and observations of biological action of somatostatin”. Recent Progress in Hormone Research 31 (1975): 321-363.
12. Richards JS. “Hormonal control of ovarian follicular development: a 1978 perspective”. Recent Progress in Hormone Research 35 (1979): 343-373.
13. Liu Y., et al. “Factors affecting menstrual cycle characteristics”. American Journal of Epidemiology 2 (2004): 131-140.
14. Westwood FR. “The female rat reproductive cycle: a practical histological guide to staging”. Toxicologic Pathology 3 (2008): 375-384.
15. Beach FA. “Cerebral and hormonal control of reflexive mechanisms involved in copulatory behavior”. Physiological Reviews 2 (1967): 289-316.
16. Lasley BL. “Methods for evaluating reproductive function in exotic species”. Advances in Veterinary Science and Comparative Medicine 30 (1985): 209-228.
17. Wallen K. “Sex and context: hormones and primate sexual motivation”. Hormones and Behavior 2 (2001): 339-357.
18. Collins PM., et al. “Influence of stress on adrenocortical function in the male tree shrew (Tupaia belangeri)”. General and Comparative Endocrinology 3 (1984): 450-457.
19. Liu Y., et al. “Factors affecting menstrual cycle characteristics”. American Journal of Epidemiology 2 (2004): 131-140.
20. de Waal FB. “Bonobo sex and society”. Scientific American 3 (1995): 82-88.
21. Ratto MH., et al. “New insights of the role of β-NGF in the ovulation mechanism of induced ovulating species”. Reproduction 5 (2019): R199-R207.