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The Organizational-Activational Hypothesis states that steroid hormones permanently organize the nervous system during early development, which is reflected in adult male or female typical behaviors. [1] In adulthood, the same steroid hormones activate, modulate, and inhibit these behaviors.
The Barker Hypothesis, or Thrifty phenotype, forms the basis for much of the research conducted on fetal programming. This hypothesis states that if the fetus is exposed to low nutrition, it will adapt to that particular environment. Nutrients are diverted towards the development of the heart, brain, and other essential organs of the fetus.
The hypothesis separately proposes that hormonal changes across the cycle cause women, when they are most likely to get pregnant, to be more attracted to traits in potential short-term male sexual partners that indicate high genetic quality, leading to greater reproductive success. [3]
The hormonal theory of sexuality holds that, just as exposure to certain hormones plays a role in fetal sex differentiation, such exposure also influences the sexual orientation that emerges later in the adult. Differences in brain structure that come about from chemical messengers and genes interacting on developing brain cells are believed to ...
For example, testosterone is lower in fathers as compared to non-fathers, [32] and preliminary evidence suggests that men may be able to discern cues of fertility in women. [33] The support for the challenge hypothesis in non-human animals provides a foundation for which to explore the relationship between testosterone and aggression in humans.
The timing hypothesis, gap hypothesis, gap theory, or critical window hypothesis for menopausal hormone therapy is a scientific theory that the benefits and risks of menopausal hormone therapy vary depending on the amount of time a woman has been in menopause upon initiation of treatment.
The concept of sexual selection was introduced by Charles Darwin as an element of his theory of natural selection. [1] Sexual selection is a biological way one sex chooses a mate for the best reproductive success. Most compete with others of the same sex for the best mate to contribute their genome for future generations.
Secondary messenger systems can be synthesized and activated by enzymes, for example, the cyclases that synthesize cyclic nucleotides, or by opening of ion channels to allow influx of metal ions, for example Ca 2+ signaling. These small molecules bind and activate protein kinases, ion channels, and other proteins, thus continuing the signaling ...