[Fis] Emergence of Human Sexual Behaviour

[Steve Watson]

Dear Rainer

Thank you for initiating this stimulating discussion. Your narrative on the emergence of human sexual behaviour is ambitious in scope and admirable in its integrative intent. By placing ritualisation at the centre of symbolic emergence and embedding human sexuality within a biosemiotic framework, you invite precisely the kind of cross-disciplinary dialogue that Foundations of Information Science aims to foster.

I would like to offer several reflections, structured around (1) the conceptual strength of your approach, (2) empirical considerations, and (3) theoretical implications concerning information and symbol formation.

First, regarding ritualisation as a mechanism of symbol emergence: your use of ritualisation—following Julian Huxley’s ethological work—as a transition from use-activity to signal-activity is theoretically compelling. This move situates symbolic forms not as sudden inventions, but as emergent transformations of already functional behaviours. Symbols, in this view, crystallise from repeated behavioural coordinations under selective pressures. That conceptual continuity between biological function and informational form is one of the strongest elements of your argument.

Applying this mechanism to human courtship behaviour—especially the proposal that inspection behaviours could have undergone ritualisation—represents an interesting and creative extension of ethological theory into anthropogenesis.

However, several elements of the specific evolutionary narrative raise questions concerning evidentiary robustness.

One issue concerns the adaptationist chain structure of the argument. The scenario is constructed as a sequential causal series: bipedalism leads to earlier weaning; earlier weaning increases infant risk; this selects for suppression of fertility swelling; persistent male interest follows; coercion dynamics emerge; permanent adipose breasts function as deceptive lactation signals; inspection behaviours are ritualised; contraception produces futile ovulation and menstruation; ovarian depletion lowers menopause age; grandmothering increases reproductive success; demographic expansion follows.

Each link may be plausible in isolation. Yet when combined into a single linear chain, the explanatory burden becomes very high. If one step is weakened, the dependent steps become unstable. Evolutionary history is often more reticulate and multi-causal than such linear reconstructions suggest. Clarifying which steps are essential to the thesis and which are heuristic would strengthen the model.

A particularly delicate component is the hypothesis that permanent adipose breasts evolved primarily as anti-coercion deceptive signals. Signalling theory suggests that deceptive signals are often evolutionarily unstable unless constrained by costs or enforcement mechanisms. Alternative hypotheses—fat storage byproduct, honest signal of reproductive value, sexual selection, pair-bond reinforcement—remain active and empirically viable. At present, the evidence does not decisively privilege the anti-coercion account. The proposal would benefit from explicit, discriminating predictions that could in principle falsify it.

Similarly, the suggestion that successful contraception led to futile ovulation and regular menstruation is innovative but currently lacks strong mechanistic support. Evolutionary explanations of menstruation remain contested and diverse. A clearer account of physiological pathways would be necessary to substantiate this connection.

With respect to menopause and the grandmother effect, while there is meaningful support for grandmothering hypotheses, the topic remains debated. Moreover, recent primate research complicates sharp contrasts between humans and chimpanzees regarding post-reproductive lifespan. Thus, integrating menopause into the scenario is conceptually elegant but empirically provisional.

>From an information-scientific perspective, further clarification may also be helpful. When describing breasts or swellings as “sex symbols” or “information tools,” it is important to specify what is meant by information. Is it conceived in a Shannon-type transmission sense, a functional selection sense, or a relational coordination sense? The narrative occasionally risks reifying symbols as objects that carry information, rather than describing them as stabilised patterns of interaction within coupled organisms. Emphasising the relational dimension of signalling may strengthen theoretical coherence within the Foundations of Information Science context.

Finally, the text connects deep evolutionary dynamics to contemporary phenomena such as sexual harassment, divorce rates, and declining birth numbers. While exploring long-term behavioural legacies is legitimate, caution is warranted. Contemporary sexual behaviour is deeply shaped by cultural, economic, institutional, and technological factors. Any evolutionary inheritance operates within these higher-order symbolic systems. Distinguishing between speculative evolutionary predispositions and modern socio-cultural dynamics would enhance explanatory precision and avoid unintended normative implications.

In conclusion, your scenario is bold, integrative, and intellectually generative. Its strength lies in provoking dialogue and in foregrounding ritualisation as a mechanism for the emergence of symbolic coordination. At present, however, the evidentiary scaffolding appears insufficient to support the full sequential model as more than a plausible reconstruction. Clarifying empirical commitments, alternative hypotheses, and falsifiable predictions would significantly strengthen the contribution.

I look forward to further discussion.

With collegial regards,

Steve Watson


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From: Fis <fis-bounces at listas.unizar.es> on behalf of Rainer Feistel (IOW) <rainer.feistel at iow.de>
Date: Thursday, 12 February 2026 at 10:11
To: fis at listas.unizar.es <fis at listas.unizar.es>
Subject: [Fis] Emergence of Human Sexual Behaviour


FIS: Foundations of Information Science (https://urldefense.com/v3/__https://fis.sciforum.net/__;!!D9dNQwwGXtA!SWArXTJgrFqaKxuGdtza52kAuOW2jKH-JIrAx79sHQp1QfshqFkKIWMw9Kf6vzSoS_yIUpqKVp_VpwKxkJh1$ <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!SWArXTJgrFqaKxuGdtza52kAuOW2jKH-JIrAx79sHQp1QfshqFkKIWMw9Kf6vzSoS_yIUpqKVp_Vp2UXzLmU$ <https://urldefense.com/v3/__https://doi.org/10.1016/j.biosystems.2025.105598__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541eOyxoBfw$>
Feistel, R. (2023): On the Evolution of Symbols and Prediction Models. Biosemiotics 16, 311–371. https://urldefense.com/v3/__https://doi.org/10.1007/s12304-023-09528-9__;!!D9dNQwwGXtA!SWArXTJgrFqaKxuGdtza52kAuOW2jKH-JIrAx79sHQp1QfshqFkKIWMw9Kf6vzSoS_yIUpqKVp_Vp75Y47Ox$ <https://urldefense.com/v3/__https://doi.org/10.1007/s12304-023-09528-9__;!!D9dNQwwGXtA!TC2CF1FSxOwksszfRibYo-j0C5j9X5Cs5vqGu7HETa00ZgkgNYYHGXR8xptIeqtIIXPKzi_jI3a9XLFc541eNp-bGc4$>



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Note: New Email Address: rainer.feistel at iow.de<mailto: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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