[Fis] Emergence of Human Sexual Behaviour

[Pedro C. Marijuán]

Dear Rainer,

Thanks for the intriguing --and exciting-- text. In order to make more 
complete a sense of your hypothesis, the paper in BioSystems (your first 
ref. below) is highly recommended. We have had quite recently a 
discussion on the Origins of Art ("Arts and the Cognitive": 
https://listas.unizar.es/pipermail/fis/2026-January/004667.html ), and 
one of the arguments raised was about aesthetic preference for visuaL & 
sound forms related to the neotenic process of our species. I referred 
to Manfred Clynes' sentic forms, and in my opinion they also appear in 
the design of female breast and in the general more rounded forms of 
feminine bodies. The panorama of human evolution involves so many 
physical, cognitive, and behavioral processes of change, than one is 
tempted to ask how was it possible at all with so few generations 
involved --around 200.000?? If one contemplates in a rough count the 
brain, hand, feet, knee, hip, tongue, larynx, spine, skin, face... with 
most of the changes densely interrelated, the result appears as an 
admirable almost impossible algorithmic economy. Could overall processes 
of general change of timing (neoteny) facilitate the whole genetic 
search? Concerning sex, the obscurity about one of the most conspicuous 
traits of our species --the bust-- and the tug of war female/male in 
reproductive terms has been substituted by ideological narratives that 
contribute little to understand the underlying 
processes/conflicts/complementarity between the sexes. Your paper is a 
brave attempt in that regard. Hope it will achieve the attention & 
recognition it deserves.

Best --Pedro

El 11/02/2026 a las 11:08, Rainer Feistel (IOW) escribió:
>
> *FIS: Foundations of Information Science*(https://urldefense.com/v3/__https://fis.sciforum.net/__;!!D9dNQwwGXtA!XQgZuz6gFfWibHF8hXbHYIpsjvNlrHim3TYER9fqGvoQ85jyX-2ZY8Yee6-YRbgHAq9Vqi2H5hcZV-OSMEvDtwkz1EW6$ )
>
> 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!XQgZuz6gFfWibHF8hXbHYIpsjvNlrHim3TYER9fqGvoQ85jyX-2ZY8Yee6-YRbgHAq9Vqi2H5hcZV-OSMEvDtxSi9j_N$  
> <https://urldefense.com/v3/__https://doi.org/10.1016/j.biosystems.2025.105598__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541eOyxoBfw$>_
>
> Feistel, R. (2023): On the Evolution of Symbols and Prediction Models. 
> Biosemiotics 16, 311–371. https://urldefense.com/v3/__https://doi.org/10.1007/s12304-023-09528-9__;!!D9dNQwwGXtA!XQgZuz6gFfWibHF8hXbHYIpsjvNlrHim3TYER9fqGvoQ85jyX-2ZY8Yee6-YRbgHAq9Vqi2H5hcZV-OSMEvDt-MtNEmo$ 
>
>
> -- 
> 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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