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The challenge hypothesis outlines the dynamic relationship between testosterone and aggression in mating contexts. It proposes that testosterone promotes aggression when it would be beneficial for reproduction, such as mate guarding, or strategies designed to prevent the encroachment of intrasexual rivals. [1]
Aggression is a multi-dimensional concept, but it can be generally defined as behavior that inflicts pain or harm on another. [ 2 ] The genetic-developmental theory states that individual differences in a continuous phenotype result from the action of a large number of genes , each exerting an effect that works with environmental factors to ...
Testosterone is the primary male sex hormone and androgen in males. [3] In humans, testosterone plays a key role in the development of male reproductive tissues such as testicles and prostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair.
A 2017 meta-analysis of fetal testosterone levels found that fetal testosterone levels (measured by the 2D:4D digit ratio) had only a small effect size of 0.036 on aggressive or violent behavior. The authors further concluded that "the 2D:4D digit ratio is neither strongly nor reliably related to aggressive or violent behavior".
The hypothesis has been subsequently expanded and modified to predict relationships between testosterone and aggression in other species. For example, chimpanzees, which are continuous breeders, show significantly raised testosterone levels and aggressive male-male interactions when receptive and fertile females are present. [96]
The relationship between testosterone and aggression is highly debated in the scientific community, and evidence for a causal link between the two has resulted in conflicting conclusions. [ 50 ] [ 51 ] [ 52 ] Some studies indicate that testosterone levels may be affected by environmental and social influences.
An enzyme called 5-alpha reductase converts a small percentage of testosterone into DHT on ... of your male secondary sex characteristics, like a deep, masculine voice and your facial and body ...
A common explanation for this phenomenon is the higher testosterone levels in males. Testosterone levels have a direct effect on neurotransmitter functioning contributing to physical aggression. Mutations affecting neurotransmitters, as stated above, are the dominant cause of changes in aggressive behaviour.