[Fis] Emergence of Human Sexual Behaviour

[Rainer Feistel (IOW)]

*FIS: Foundations of Information Science*(https://urldefense.com/v3/__https://fis.sciforum.net/__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541ei259VdY$ )

Discussion kickoff narrative by Rainer Feistel, 11 Feb 2026

*Emergence of Human Sexual Behaviour*

Natural evolution invented symbols as information carriers, universally 
exploited by any living being in various forms. As a rule, 
self-organised symbols appear by ritualisation, a qualitative transition 
from behavioural use-activities to related signal-activities, as 
discovered by Julian Huxley in 1914. Numerous novel and unparalleled 
symbols emerged in the course of anthropogenesis. Sex symbols, or 
courtship habits, are typically unambiguous intra-species information 
tools, governing the species’ reproduction behaviour by starting and 
terminating the mating season.

Permanent adipose mammary glands recognised as sex symbols are unique to 
humans only. If those emerged by a ritualisation transition, what may 
have been the use activity they had originated from? Anatomically, the 
most likely such activity is breastfeeding. However, lactating female 
mammals are generally infertile and typically avoid any mating 
activities in favour of their childcare. “The verdict is still out on 
why the permanent breast evolved in humans” wrote Deena Emera yet in 2024.

Fossil and genetic evidence is consistent with the plausible hypothesis 
that the last common ancestor (LCA) of humans and great apes lived about 
7 million years ago and was similar to recent chimpanzees. The sexual 
behaviour of the latter, however, is very distinct from that of humans. 
Female chimps breastfeed their offspring, carried on their back, for 
about five years. Premature weaning poses a high lethal risk to the 
helpless infant. After weaning, females develop a prominent anogenital 
swelling as a sex symbol that invites males to mate. It is exclusively 
then that males show relevant sexual interest, and preferably in old 
“ugly” females. How may human sex life have evolved from such foreign 
roots during a relatively short period of history? Likely, the radical 
change was enforced by violent selective pressure.

When the LCA gradually turned to bipedalism, carrying older, heavier 
infants on the back became impractical and weaning occurred earlier, 
with increasing risks for the offspring and generally reduced 
reproduction rates. Females suppressing the fertility swelling protected 
the toddler by preventing early pregnancy. Males responded with 
permanent sexual interest also in non-swollen females. Females reacted 
with repulsive frigidity, males in turn with coercive mating. Already 
from a distance, ostentatious adipose breasts, perfectly imitating 
lactating ones, prevented coercive male approaches, who in return 
started closer visual, manual or oral inspection of the nipples in order 
to check fertility and reveal the possible fake. Successful 
contraception by fertile females caused periodic futile ovulation and 
subsequent regular menstruation. The resulting ovary depletion lowered 
the menopause age into the lifespan, so that old females became 
infertile and could take care of their grandchildren when the mother 
became pregnant too soon. This grandmother effect raised the 
reproduction rate substantially, supporting enhanced migration pressure 
on the younger generation. The previous inspection of female nipples and 
genitals was no longer a necessary use-activity and turned into a 
courtship habit of humans by a ritualisation transition, similar to that 
of waterfowls originally discovered by Huxley.

This is a speculative narrative of how the ritualisation of human sexual 
behaviour was possibly caused by the transition to bipedal gait. The 
genetic heritage of those old days may still influence the social 
behaviour of modern humans and may be part of contemporary sexual 
conflicts, such as sexual harassment, high divorce rates or declining 
birth numbers in liberal societies. Causal mental models are key for 
understanding the origin of such problems rather than just lamenting and 
deprecating their symptoms. Finding suitable compromises between 
mutually inconsistent sexual interests may provide a challenging but 
promising future solution, rather than implementing restrictive, 
one-sided patriarchal or matriarchal social suppression systems.

*Further reading*:

Feistel, R. (2025): Bipedalism, childhood, and ritualisation of human 
sexual behaviour: A hominin model scenario of ontogenetic selection. 
BioSystems 257, 105598. 
_https://urldefense.com/v3/__https://doi.org/10.1016/j.biosystems.2025.105598__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541eOyxoBfw$  
<https://urldefense.com/v3/__https://doi.org/10.1016/j.biosystems.2025.105598__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541eOyxoBfw$ >_

Feistel, R. (2023): On the Evolution of Symbols and Prediction Models. 
Biosemiotics 16, 311–371. https://urldefense.com/v3/__https://doi.org/10.1007/s12304-023-09528-9__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541eNp-bGc4$ 


-- 
Note: New Email Address:rainer.feistel at iow.de
Dr. rer. nat. habil. Rainer Feistel
Physicist (emeritus)
PS Gustav Hertz Prize, Berlin 1981
CITAC Best Paper Award, Paris 2011
IAPWS Honorary Fellow, London 2013
BIPM Metrologia Highlight Articles, Paris 2016
EGU Fridtjof Nansen Medal, Vienna 2018
LS Daniel Ernst Jablonski Medal, Berlin 2021
IAPWS Gibbs Award, Boulder, Co., 2024
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