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While cell autonomous sex identity emphasizes the intrinsic sex-specific properties of individual cells, the interplay between CASI and hormonal influences plays a critical role in shaping an organism's overall sexual phenotype. CASI and hormones are not mutually exclusive but instead represent complementary mechanisms of sexual differentiation.
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. [2]
The acid-growth hypothesis is a theory that explains the expansion dynamics of cells and organs in plants. It was originally proposed by Achim Hager and Robert Cleland in 1971. [1] [2] They hypothesized that the naturally occurring plant hormone, auxin (indole-3-acetic acid, IAA), induces H + proton extrusion into the apoplast.
Afterwards, the hypothesis was formulated in terms of population genetics by Fisher (1930) [12] and Muller (1932) [13] and with greater mathematical formalism, by Muller (1958, 1964) [14] [15] and Crow and Kimura (1965). [16] The doubts about the validity of the Vicar of Bray hypothesis caused the upcoming of alternative hypotheses such as:
However, the dual-hormone hypothesis also has its own flaws, and current evidence appears to only partially support the hypothesis, according to a meta-analytical evaluation in 2019 by Dekkers et al. [36] A proposed reasoning for the occasional weak evidence is that cortisol and testosterone, further interact with social context and individual ...
In humans, barring intersex conditions causing aneuploidy and other unusual states, it is the male that is heterogametic, with XY sex chromosomes.. Haldane's rule is an observation about the early stage of speciation, formulated in 1922 by the British evolutionary biologist J. B. S. Haldane, that states that if — in a species hybrid — only one sex is inviable or sterile, that sex is more ...
This led scientists to look for somatic markers for prenatal hormonal exposure that could be easily, and non-invasively, explored in otherwise endocrinologically normal populations. Various somatic markers (including 2D:4D finger ratios , auditory evoked potentials , fingerprint patterns and eye-blink patterns) have since been found to show ...
The reproductive-cell cycle theory posits that the hormones that regulate reproduction act in an antagonistic pleiotrophic manner to control aging via cell cycle signaling; promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence. [1]