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The science of masturbation: New study traces origins of self-pleasuring
in primates
Masturbation in primates was linked to STD prevention and reproductive
success.
Sejal Sharma
Sejal Sharma
Created: Jun 07, 2023 07:48 AM EST
SCIENCE
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The science of masturbation
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A new study found that primates masturbated to safeguard themselves
against Sexually Transmitted Diseases (STDs) and to better their chances
of successful impregnation.
Researchers from University College London (UCL) were tracing the
origins of masturbation in primates when they found self-pleasuring to
be an ancient trait among the order and serves an evolutionary purpose.
Primates include lemurs, lorises, tarsiers, monkeys, apes, and humans.
Autosexual behavior, or masturbation, is a common practice across the
animal kingdom but appears to be significantly prevalent in primates.
Its evolutionary history remains elusive, given that there is little
research done to support the behavior.
The study notes that genital stimulation, on a superficial level,
doesn’t exactly serve a higher purpose in evolutionary theory. It
doesn’t increase the survival rate in primates and takes up additional
time, energy, and attention. As a consequence, masturbation became
taboo. Historically, it’s been associated with people who need a sexual
outlet necessitated by a high libido.
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But then the research team thought that since self-pleasuring is so
common throughout the animal kingdom, there has to be a bigger and
clearer explanation.
The team collated information from over 400 sources, including 246
published academic papers, 150 questionnaires, and personal
communications from primatologists and zookeepers, as per a press
release by UCL. From this data set, the researchers tracked the
distribution of self-pleasuring behavior across primates to understand
when and why it evolved in both females and males.
The team tested two theses: Postcopulatory Selection and Pathogen
Avoidance Hypotheses.
The Postcopulatory Selection hypothesis was further divided into two
constituents – the Sexual Arousal hypothesis and the Sperm Quality
hypothesis. The Sexual Arousal hypothesis revealed that non-ejaculatory
masturbation in males speeds up subsequent ejaculation or increases
ejaculate quantity which could help in fertilization. In females,
masturbation increases vaginal pH, thus creating a more hospitable
environment for the sperm. Vaginal excretions have also been known to
filter out inferior sperm and facilitate the movement of high-quality
sperm toward the uterus.
The Sperm Quality hypothesis states masturbation in males before a
sexual encounter improves sperm quality by expelling inferior sperm.
The other thesis, Pathogen Avoidance, predicted that masturbation after
a sexual encounter, in both males and females, helps prevent sexually
transmitted infections (STIs). These postcopulatory genital grooming
strategies include oral self-cleaning, urination, and masturbation to
clean the reproductive tract with ejaculation.
The significance of female masturbation remains less clear, noted the
researchers. The team says that more data on female masturbation and
sexual behavior needs to be done.
Lead researcher Dr. Matilda Brindle said, “Our findings help shed light
on a very common, but little understood, sexual behavior and represent a
significant advance in our understanding of the functions of
masturbation. The fact that autosexual behavior may serve an adaptive
function, is ubiquitous throughout the primate order, and is practiced
by captive and wild-living members of both sexes, demonstrates that
masturbation is part of a repertoire of healthy sexual behaviors.”
The study was published in The Royal Society Publishing.
Study abstract:
Masturbation occurs throughout the animal kingdom. At first glance,
however, the fitness benefits of this self-directed behaviour are
unclear. Regardless, several drivers have been proposed. Non-functional
hypotheses posit that masturbation is either a pathology, or a byproduct
of high underlying sexual arousal, whereas functional hypotheses argue
an adaptive benefit. The Postcopulatory Selection Hypothesis states that
masturbation aids the chances of fertilization, while the Pathogen
Avoidance Hypothesis states that masturbation helps reduce host
infection by flushing pathogens from the genital tract. Here, we present
comprehensive new data documenting masturbation across the primate order
and use these, in conjunction with phylogenetic comparative methods, to
reconstruct the evolutionary pathways and correlates of masturbation. We
find that masturbation is an ancient trait within the primate order,
becoming a more common aspect of the haplorrhine behavioural repertoire
after the split from tarsiers. Our analyses provide support for both the
Postcopulatory Selection and Pathogen Avoidance Hypotheses in male
primates, suggesting that masturbation may be an adaptive trait,
functioning at a macroevolutionary scale.
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