Highlights
• A new mechanism for the recent time evolution of human behaviour is proposed
• Non-genetic inheritance (NGI) and accumulation of behaviour is crucial for culture
• The human behaviourome concept is introduced
• Mechanisms of a near-orthogonal and ultra-fast NGI of the behaviourome are suggested
• Behaviourome mutations can be target-directed
• Ex-vivo storage and -accumulation of the behaviourome are pivotal for culture
Abstract: Current human culture is characterized by an increasing rate of accumulating potential and actually performed behaviours. The growth of behavioural complexity as well as the ex-vivo accumulation of human behaviour, here identified as the non-genetically inherited (NGI) behaviourome, cannot be explained by genetic/epigenetic mechanisms of inheritance. As human beings derive their socio-cultural identity predominantly from their behaviourome, mechanisms of heritability should predominantly consider inheritance and accumulation of the NGI behaviourome. Here we propose key mechanisms of a near-orthogonal and ultra-fast evolution of the NGI human behaviourome that provide a foundation not only of unique human culture development, but also of its recent acceleration. Thereby, the evolution of the human NGI behaviourome underlies similar features as genetically based evolution. However, specific mechanisms of mutation and selection work largely independent (orthogonal) from genetic/epigenetic mechanisms. We suggest a mechanism of how adaptive changes (mutations) in the NGI behaviourome work target-directed and how selection works on an ultra-fast time scale. Selection results are mostly not fatal for the individual which allows for a much increased mutation rate. For crucial accumulation of the NGI behaviourome, ex-vivo storage and retrieval systems of virtually unlimited capacity are described. We discuss the great potential of the human NGI behaviourome in respect of speculative human super-reproduction and homosexual reproduction success, as well as a possible unique human way to avoid reproduction failure in childlessness. Altogether, this model of human behavioural reproduction and accumulation of behaviour may provide a base for better understanding and prediction of uniquely human cultural development.
Keywords: behaviouromebehavioural accumulationcultural evolutionex-vivo storagenear-orthogonal evolutionnon-genetic inheritancereplication failure, super-reproductiontargeted mutationultra-fast selection
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9. Childless and homosexual reproduction success
It is speculated that a considerable part of the human population which appears threatened by reproduction failure are childless and homosexual man and women, which were denied a direct genetic reproduction. In non-human animals, the lack of genetically-related offspring and homosexuality leads to a general reproduction failure which may, however, be partly overcome by supporting kin and their offspring [182]. In humans, the individual NGI behaviourome constitutes a large part of the personal identity. This can be passed on in a gradual way, from almost complete to small traces of the individual NGI behaviourome. The individual NGI behaviourome may very well be inherited in small or even large proportions by NGI mechanisms, may it be to foster children or even children not being in any legal care responsibility. By that way, also childless and/or homosexual human individuals may reproduce their individual behavioural phenotype to a considerable extent. The degree of this reproduction may even be so large that genetically unrelated foster children are seen as a fully accepted biological offspring [242]. For example, many cuckoo children are not recognized by their fathers as not-genetically related, especially when the inherited paternal NGI behaviourome is copied to a significant degree [17].
Behavioural teaching in humans is often outsourced from the pedigree, e.g. in the kinder garden, in schools, or universities. There, teachers not only teach the macro social environment shared part of the NGI behaviourome (e.g. common knowledge and social behaviour), but also to some extent their own individual NGI behaviourome. As such, pupils may inherit always some parts of their teacher’s individual NGI behaviourome. And depending on the teacher, this can be quite large and influential for the non-kin recipients. Based on the above described proximal mechanisms of NGI, this may be one reason why teachers often prefer and treat in a more affectionate and supportive way those pupils that show a strong similarity in their individual behaviourome to the own one. When a non-kin relationship between teacher and pupil is likely or known, similarity in the NGI behavioural phenotype is preferred to similarity in the physical phenotype which would otherwise serve as a proxy indicator of genetic overlap. This may go as far as considering non-kin pupils like a “son in mind” (and behaviour), although being well aware that they are non-kin.
Even super-reproduction of the NGI behaviourome appears possible for childless and/or homosexual individuals by whom the behaviourome is transmitted to a very large population of recipients. This may or may not include homosexuality and related behaviours. Famous artists may serve here as outstanding examples for behavioural reproduction, such as e.g. Leonardo da Vinci or Oscar Wilde. Their live records (as behavioural instructions) and achievements as artists (as successful results of their NGI behaviourome) are still serving as blue prints for young artist’s attitudes and working modes. They are often seen as brilliant examples of their profession.
An as yet unanswered question in human evolution has been why do homosexuals not die out when their genome is not inherited [182]? A potential new answer to this question may be provided by NGI of the behaviourome. Homosexual partner preference and associated behavioural patterns may readily be assumed to be part of the NGI behaviourome, which is not inherited from genetic parents. At least, no genetic source for this behaviour has been discovered; neither as a preserved genetic base, nor in the shape of de novo genetic mutations [207]. Nevertheless, homosexual behaviour can be copied from non-kin and from ex-vivo sources (e.g. written records), or may be established as a de novo behaviour. Likewise, it may be passed on effectively to next generation non-kin, and become ex-vivo stored. But how is it providing any fitness benefit for those who copy and express it? The advantage may be in saving on resources that heterosexual individuals have to spend on genetic reproduction. This may set capacity free to innovate new NGI behaviours and to develop more sophisticated NGI behaviouromes that can contribute more than average to the general population NGI behaviourome pool and, thus, to culture. And as long as cultural advancement, i.e. the qualitative or quantitative expansion of the NGI behaviourome, is rewarded in a human society and enhances chances of survival for the individual, this behavioural trait may remain in the NGI behavioural pool. Nonetheless, it should be noted that certain societies do actively punish the behavioural trait of homosexuality and its in-vivo and ex-vivo inheritance and replication. Gay people are threatened by death penalty and books/movies about this behavioural phenotype are prohibited and prosecuted. The relative persistence of this behaviour may arise from the delayed nature of the cultural benefit. While the perceived threat of genetic replication failure is immediately perceived by a group, the potential benefits in cultural advancement are delayed. As such, the behavioural trait of homosexuality is submitted to a reward discounting in a group/society, which can yield opposite outcomes depending on how immediate vs. delayed reward are valued. If the immediate risk of replication failure is valued higher, the behavioural trait may become supressed, i.e. actively punished by society. If the delayed reward is valued higher, homosexuality may become accepted and even actively rewarded.
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11. Empirical testing of the proposed mechanisms of a near-orthogonal ultra-fast evolution of human behaviour in culture development
Here, we described a mechanism of human NGI behaviourome evolution that was characterized as near-orthogonal and ultra-fast acting compared to genetic/epigenetic based evolution and claimed it to be a major source of present day human culture. As this is currently only a speculative account, all components of this claim would need empirical testing and the opportunity of falsification. This may be done by addressing each feature separately.
The “near-orthogonal” claim can be falsified when evidence shows that the human NGI behaviourome has a predominant genetic/epigenetic base that essentially displays the same temporal dynamic change as the human behavioural phenotype. For that, it would be an important research goal to empirically classify the full human NGI behaviourome in all its current complexity and to empirically monitor its changes closely from now on. From the starting point of a categorized present day human NGI behaviourome, one should estimate backwards its dynamic change over the last five thousand years. This may be paralleled by measurements of the human genome/epigenome development backward and forward. Behavioural and genetic/epigenetic data may then allow testing of whether and to what extent the dynamic development of the human behaviourome over that time is best described by a process near-orthogonal and, thus, largely independent from genetic/epigenetic evolution. Likewise the “ultra-fast” nature can be tested by comparing time scales and the degree of behaviourome change. Time scales for alterations of the human genome/epigenome that are known to have changed human behaviour and the dynamic of behavioural changes for which no genetic base can be identified, may be compared in the relevant 5000 years.
A proposed unique characteristic of the evolution of the human NGI behaviourome is its capability for targeted mutations of behaviour, e.g. during puberty. Thereby, the proposed Lamarckian mechanism may be experimentally tested in longitudinal studies where single parental behaviours may be artificially introduced that would be mildly maladaptive for the offspring, and trans-generational mutation rate is measured together with rate and quality of newly invented behaviours that can replace the abandoned/non-replicated ones. However, when ethical concerns should limit this experimental approach, also quasi-experimental post hoc analysis of behavioural mutations during puberty would provide some clues.
If the claim that the presented mechanism is a major driving force for human culture, it would be critical to test for an accumulation of the NGI behaviourome, i.e. the sheer number of human behaviours should increase in the relevant time span, which should not be paralleled by an increase in behaviourally relevant genes or epigenetic modifications.
12. Summary and outlook
If a biological, psychological or cultural theory of evolution wishes to explain development and current diversity of life, it also has to capture the present appearance of human beings. It has to provide a reasonable account of its radical transformation in the last few thousand years. Here we tried to identify and characterize mechanisms of a near-orthogonal and ultra-fast evolution of human behaviour which serve as an essential prerequisite for human cultural development in the last 5.000 years of human history. In that they are not meant to replace a genetic/epigenetic based evolution, but to largely expand them by mechanisms which allow to better explain many features of human culture that cannot be readily captured by genetic evolution. The Darwinian account of evolution comprises all living beings on earth, may they express behaviour or not. Human behavioural evolution theory, in contrast, captures only a relatively small aspect of biology, the NGI component of the human behaviourome. Nevertheless, this is the one that has submitted the surface of earth to probably the most profound changes induced by living species ever recorded in the history of life on earth, with significant effects on virtually all other species and on inanimate nature. Among those changes is what we consider as human culture, a vast array of NGI behaviours that are no longer genetically coded, but inherited, externally stored, spread and accumulated. In that the present account attempts to provide an explanatory scheme of how distinct genetically inherited features gave rise to human culture.
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