Jovo Tosevski (School of Medicine, University of Kragujevac, Serbia and Montenegro),Dusica Lecic Tosevski (Institute of Mental Health, School of Medicine, University of Belgrade, Serbia and Montenegro)Summary (по-русски)
BACKGROUNDIt has been maintained by many authors, based on DNA sequences analyses, that the first Homo sapiens appeared approximately 200,000 years ago directly from the Homo erectus evolutionary line in a single region and a single evolutionary nucleus with a common female ancestor ("mitochondrial Eve"). According to the same hypothesis, man spread "out of Africa" [1-6]; however, the combined genetic and fossil evidence has not yet completely decoded the origin of man [7]. Anatomists long believed that we are closely related to other living anthropoids. Advanced biochemical methods strongly confirm this view at the genetic level [8,9]. An incredible genetic similarity was found, particularly between the man and the chimpanzee, by the DNA-DNA hybridization method [10,11]. Indeed, the improved methods of DNA analysis have also confirmed that human and chimpanzee genomic sequences were virtually identical. Depending on the authors, the estimates range from 95% to 98.8% of base pairs shared between chimpanzee and human DNA [12,13]. However, there are disturbing discrepancies. Humans differ anatomically from chimpanzees much more than one would expect based on the similarities of DNA and many proteins. The differences in the overall shape of humans and chimpanzees are much greater than the differences found in their gene structures, i.e. human and chimpanzee genomes are fully identical at the nucleotide level. However, morphological traits, brain size, and the cognitive abilities of the two species are distinct [13]. In comparison with chimpanzees, for example, the human brain is 250% heavier, while the body is only 20% heavier [14]. Definitely, the human brain is strikingly different in its abilities from the brain of any other species, including the anthropoid apes, despite the extreme similarity of genetic material. Here we will hypothesize the human female's credit for the general course of the evolution of man. This includes the de facto altered morphology of the body, in particular of the female pelvic region, thanks to complete bipedalism. The altered morphology of the female pelvis might have had a morphological-psychological influence on the formation of the emotional-cognitive potential and the overall psychology of our species through the model of concealed external female genitals, i.e. the vulvo-cryptic phenomenon. BIPEDALISM AND THE VULVO-CRYPTIC PHENOMENON OF THE HUMAN FEMALEThe first hominids (Australopithecines) using a habitual upright bipedal gait are believed to have evolved in Africa five to six million years ago [15,16]. However, this was just the beginning of the evolutionary line that has led to present-day human bipedalism. Within the genus Homo it has been widely accepted that Homo erectus might have been the species whose upright posture, more advanced compared with that of earlier hominids, enabled it to walk in a way rather similar to the way we do today [17]. Keeping in mind that the evolutionary history of human bipedalism required highly specific adaptations of the skeletal and muscular apparatus [18,19], a greater diversity of bipedalism can be expected [20]. This probably ranged from an unknown mixture of climbing and bipedal walk to, ultimately, the remarkably enduring bipedal walk of humans [21]. The erect human posture is unique among primates. Complete bipedalism, the origin of which involved complex morphogenetic factors, is characteristic only of man. This unique type of bipedalism is a consequence of dramatic changes in the course of the evolution of man. The changes occurred primarily on the vertebral column, pelvis, and large joints of the lower limbs, above all the hip and the knee. Furthermore, maintenance of trunk balance and improved stability in the upright posture of man are achieved with the help of large muscles of the vertebral column, such as the erector spine group, abdominal (external and internal obliquees), and gluteal group (gluteus medius and minimus) [22]. Novel human anatomical features, such as a broader ilium, broader sacrum, longer femoral neck and pubic rami, shorter ilium and pubic joint [23], transformed the incomplete bipedality of man's ancestors into a highly specialized complete bipedalism. This type of bipedalism implies the creation of new biomechanical principles with a tendency towards vertical alignment of the gravitational centers of the head, thorax, abdominal masses, and lower limbs [24]. The center of gravity in humans lies near the hip joint and the line of gravity falls slightly anterior to the ankle joint [22]. In this regard, changes in the pelvis are of special interest. The anatomical peculiarities of the human pelvis are numerous and unique. The lumbar and sacral angles (both forming the lumbosacral angle) are almost equal in all mammalian species, and the development of the lumbosacral angle appears to be related to the progressive acquisition of erect posture and the ontogeny of bipedal locomotion. From the early australopithecines, the lumbosacral angle increased over that in apes and reached its maximum in H. sapiens [25]. The levator ani muscle, well developed in H. sapiens, also affects the lower part of the sacrum and coccyx and influences its ventral orientation [26]. Due to the fact that the ischial spines in humans are prominent and located more toward the front, the pelvis floor became narrower [27]. In addition, the final shape of the female pelvis seems to have been determined by culture and environment as well as by genetics [28]. The fact that the sacral promontory moved toward the pubic symphysis is significant. This resulted in a shortening of the anteroposterior diameter and a widening of the transverse diameter of the human pelvis [29]. The shortening of the anteroposterior diameter and widening of the transverse diameter inevitably led to the moving of all the contents of the pelvic floor toward the symphysis, including the external genitals, causing them to become concealed and practically inaccessible in women, both in erect and in supine posture. Indeed, no fact or hypothesis to do with human bipedalism contradicts the fact that, after all the evolutionary bodily transformations, the external sexual organs of women are located at the most inaccessible place of the female body, i.e. in the front part of the pelvic floor below the pubic symphysis. The human great gluteal muscle is placed in the most posterior position in the gluteal region, acting as an extensor of the lower limb [30]. Our opinion is that the great gluteal muscle also has the function of concealing the female genitals from the rear part of the body. As it is more prominent in the female due to her more prominent adipose tissue, its role in concealing the female genitals from the dorsal side and making them inaccessible becomes even more important. Since the same muscle of the chimpanzee has an anterior position [22], it does not conceal the genitals even in the detumescent phase of the chimpanzee female. It seems that the role of this muscle in bipedalism is parallel to its role in concealing the external human female genitals. The unique position of the external human female genitals is clearly visible if compared with that in anthropoid apes, the only living comparable group of higher primates. In fact, a simple comparison of morphology and the position of the genitals of living anthropoids, for example of chimpanzees and of the external sexual organs of human females, shows obvious differences. Morphological differences of the external sexual organs of chimpanzee females and human females are presented in Table 1. Table 1. Comparative morphology of the female external genitals.
The external genitals of the chimpanzee female are most visible and fully accessible to the male during copulation. The situation with the external genitals of all mammalian species is almost equal, because the external female genitals are easily accessible to the male, thus making the consent of the female to copulation during the mating season more or less trivial. The accessible and visible genitals of the female are an easy target for the male and, due to the exposed position of the external female sexual organs, the male's copulation intent can hardly be frustrated. In contrast to other mammalians, the external sexual organs of human females are concealed and not easily accessible to man. Because of this, sexual intercourse requires the woman's consent; consequently, the woman can foil the man's copulative intention or consent to it willingly. The anatomical characteristics of the human female vaginal canal and the position of the uterus are also unique for the same reason: the external genitals are moved forward and toward the pubic symphysis. While in other mammals and apes the uterus axis continues from the axis of the vagina with only a slight deviation, which enables easy delivery, this is not the case with human females. The uterus in humans is inclined forward and covers a sharp angle with the cervix. Furthermore, rather than the cervical axis continuing from the vaginal axis as in all other primates, the human cervix and vaginal axes comprise another sharp forward angle. The vagina is found to be a curved organ with a distinct upper portion that has an axis between the third and fourth sacral vertebrae [31] and with an average vaginal length of about 9 cm [32]. Another indicator that points to the shifted position of the external female genitals forward is the emergence of sacral nerves in the anterior part of the body. Human sacral spinal nerves innervate the posterior part of the lower extremities, while the lumbar nerves innervate their anterior part [33,34]. The emergence of the sensitive nerves (posterior labial nerves) arising from the S2-S3 spinal sacral segments at the anterior-inferior side of the genital region also confirms that the external genitals have been moved forward. The changed position of the sexual organs resulted in a new feature with morpho-psychological implications, i.e. concealed external genitals. Bipedalism is in itself the primary cause of this new characteristic of the human female in which copulation only becomes possible with female consent because the external opening of the vagina, the vulva, has been turned forward and placed downward on the pelvic floor. It is clear that bipedalism was not a solid basis for survival per se. All bipedal hominid forms except modern man have disappeared. It seems that only human bipedalism was successful even though the upright posture of modern man was a direct cause of several inefficient biomechanical solutions and diseases that are entirely human (low back pain, sciatica, varicose veins, etc.). Still, it is a low price that our species has paid compared with the avalanche of evolutionary progress which complete bipedalism brought. PSYCHOLOGICAL CONSEQUENCES OF THE HUMAN FEMALE VULVO-CRYPTIC PHENOMENONBrain expansion and speechThe dramatic evolutionary enlargement of the human brain represents one of the most rapid morphological changes in evolution. The total human brain mass, particularly its neocortical part, progressively growing in the course of evolution, settled in modern man at the weight of 1,350–1,450 g approximately 0.2–0.4 million years ago [14,35]. The human brain presents a manifold functional, developmental, and evolutionary mystery. The principal question is what made it expand so much, unlike that of any other species. In other words, “where did the neocortex come from?” All other animal species have a brain smaller than that of man, and this presents no obstacle to their successful survival. Man alone needs a brain of that size, unlike any other species. The attempt to explain the enormous brain expansion and the existence of new cortical areas in man by introducing a specifi c “single, magic molecule” not present in other primates is highly implausible in view of the fact that almost all the receptors, ionic channels, and transmitters have also been found in the brains of all other mammals [36]. There are diverse opinions purporting to explain the manner of expansion of cortical areas of the brain. Some of them, such as, the “protomap and radial unit” hypothesis of cortical parcellation [37], are well founded. Although the genetic basis of brain expansion has not yet been sufficiently explored, according to certain hypotheses there may exist individual underlying genetic components acting through positive selection. An example thereof is the evolution of the human ASPM (abnormal spindle-like microcephaly-associated) gene as a possible determinant of brain size [38–40]. So far, no mechanism has been offered that would provide a satisfactory answer to the question of what led to such rapid enlargement of the human brain. Highly important in this respect are substantial cytoarchitectonic data indicating that there exists a distinct increase in neocortical areas in man (approx. 50–70) compared with primitive mammals (approx. 20–30) [41–43]. This includes the human thalamic mediodorsal complex, which is also larger than would be expected based on the brain weights of the subhuman primates [44]. The central question elicited in this issue is how the shifting forward of the human female genitals and their consequent inaccessibility to the male might have contributed to the creation of a highly organized emotional-cognitive human being. To begin with, the process of humanization, socialization, and transformation of the primitive primate basis of behavior into human forms of behavior implies well-known qualities. These include brain expansion, overall quantitative and qualitative increase in memoric capacities of the human brain, increased emotionality coupled with efficient memorization, as well as articulation of emotional-cognitive content through the emergence of speech. The process of fundamental reorganization of the non-human primate brain into the human brain must have taken place in parallel at all levels, but primarily in the limbic brain, responsible for emotional functions, as well as in the neocortex, containing cognitive characteristics of the species. We believe that the human female genitals, having been moved forward and thus concealed as a new quality and adaptation, might have made the reproductive success of the male dependent on conscious female consent to mating. This is a very strong reason for initiating positive selection aimed at accelerated development of emotional and cognitive systems that would improve motivation, planning, action, and socialization in all spheres of life. The early evolutionary psychological interactions at the time when our species chose the miraculous model of creating an emotional and cognitive matrix for its own expansion are impossible to prove with material data, since those are “unfossilized” phenomena. Emphasizing the difference between natural and sexual selection, Darwin stressed that natural selection depends on both sexes, while sexual selection depends on same-sex individuals, undertaken in order to show their sexual attraction [45]. The process of sexual selection is sufficiently stimulating in increasing sexual attraction within the typical sexuality existing in all mammals, among which mating is based on simple sexuality and the sexual act does not have the prolonged psychological repercussions typical in man. Cortical activity and consciousness are dominant functions in man, while sexual attraction of the human female has been raised to the highest possible level compared with females of all other animals. In addition, apart from the striking natural attractiveness, the human female is in a position to heighten her attraction consciously by using artificial means (clothes, makeup, etc.). Of course, a particularly important question has to do with speech. Current thinking suggests that many areas of the neocortex and subcortical structures support the corticalstriatal-cortical circuits that confer complex syntactic ability, speech production, and a large vocabulary [46]. There are also suggestions that some groups of genes (human FOXP2) might also support such a complex function. Two functional copies of it seem to be required for acquiring normal spoken language [47]. However, the inevitable question repeatedly posed is why the creation of speech and language was necessary, as most high-order mammals survive quite well with primitive sounds and gesture communication. It is generally accepted that an important reason for brain expansion is the evolutionary necessity for human language and other high-order cognitive functions and that it was caused by adaptive selection [48]. The need for language and the presence of high-order cognitive functions would no doubt justify such a dramatic brain expansion, including the already posed but unexplained principal questions as to what was the purpose of these unusual and unprecedented tools in the evolution of primates, such as speech and cognitive capacity. In our view, the answer might be simpler than we imagine: they might be instruments of entirely new functions, i.e. increased inter-sexual communication and increased female influence on the male in every sphere of life and interpersonal relations. Speech is of paramount cognitive importance in overall human communication. However, little attention is given to another extraordinary characteristic of speech, namely to the fact that speech is the best means of creating fallacy and misunderstanding. Indeed, among the many means to such end in living nature, human speech is the most powerful. However, who needs fallacy and misunderstanding, and for what reason? It seems that it is the inevitable companion of psychosexual manipulation, which is, in our opinion, a positive evolutionary characteristic. The new human female morphology caused a number of psychological consequences due to the possibility of propellant female psychosexual manipulation, that is, conditioning of the man during copulation. The ability of the female to consciously decide on whether copulation will take place might be related to some new psychological traits of the male. The wellknown “inconstancy” of the female nature, unduly considered by males to be an ego-syntonic trait, could be a deeply rooted evolutionary imperative. On the other hand, because of the position of the female sexual organs, male access became roundabout, via the visible sexual characteristics that the female body offers instead of the concealed genitals, the chief target of the male. Even though the concealment of the female sexual organs probably existed in some form in all late hominids, the first effect of that unique evolutionary venture is clearly visible only in the human female. The concealed external sexual organs of the female became attractive in a special way when the female acquired “general” attributes of beauty, i.e. she lost body hair and drew attention to the secondary sexual characteristics, e.g. breasts, lips, skin, figure, and voice. There is evidence that physiological and anatomical adaptations are not primitive remnants from a primate ancestor, but recently acquired characteristics of our genus [49]. Paradoxical as it may seem, misunderstanding between the sexes in our species is useful because it causes a positive increase in tension between them, thus generating new interactions. As the phylogenetic basis of the curiosity of primates is ensured, each misunderstanding will generate some reaction. The emotional-cognitive ability of each individual is responsible for whether a misunderstanding will turn into a harmful type of conflict or take a stimulating direction. For instance, an important source of gender misunderstanding are the evident sex differences in jealousy-evoking behavior towards a rival to whom one’s partner might feel attracted. Men are more jealous when a rival is high in physical dominance and social status, whereas women are more jealous when a rival is high in physical attractiveness [50]. In the hypothetical evolutionary period when the female morpho-psychological capacity was functionally established, its effects emerged, especially on the male surroundings. As sexual union was not guaranteed in advance, men and women expanded their activities in non-sexual social contacts, which became a major part of their daily activities, motivation, imagination, and working zeal. However, most of the time the woman was aware of her superiority in the male-female relationship, and “complicated” it with new demands, resulting in her increased participation in love games and her overall influence. The woman held all the key elements of sexual communication in her hands. The male’s physical strength and skill in the external environment were restrained by the female's morphological and psychological offer that the male could never resist. The female, continuously sexually receptive, was "offered" to the male, thus presenting a permanent challenge to him. Emotionality, memory, behavioral sex dimorphism, and intersexual relationsThe socioemotional behavior and neurobiological position of humans in the living world are quite complex and represent particularly thorny problems. Humans have the greatest cognitive abilities in the living world, but they are also the most emotional creatures of all other primates. The limbic system is a functional whole, essential for emotional processing and behavior, and composed of groups of nuclei and parts of cortex of diverse topological, cytoarchitectonic, and phylogenetic characteristics. As we know, neocortical expansion in humans made possible the creation of the high-order cognitive functions and the appearance of the developed prefrontal cortex and posterior parietal cortex, making humans in turn capable of the functions of cognition, planning, and purposeful actions. Numerous data confirm the strong functional and very specific interaction between the limbic nuclear structures, such as the amygdala, hypothalamus, bed nucleus of the striae terminalis, and ventral periaqueductal gray, and cortical structures, such as the archicortex of the hippocampal formation, prefrontal limbic cortices, fronto-parietal cortex, and temporal cortex [51,52]. The amygdala as an emotional processor and the prefrontal cortex as a cognitive processor [53] have the leading role in the functional links between nuclear and cortical structures. There is clear evidence pointing to the linkage between neocortical and amygdaloid evolution, and especially basolateral and lateral amygdaloid nuclei correlate strongly with the neocortical sensory, temporal, and prefrontal area. [54,55]. In anthropoid brain, the neocortex and the amygdala are unusually profusely connected compared with other mammals [56]. There are abundant data indicating that the role of the amygdala is of paramount significance in creating emotions and forming emotional memory as well as fear memories [57,58], while the hippocampus and entorhinal cortex are of utmost importance for declarative memory [59]. There are also data pointing to a reciprocal dependence between the amygdala and hippocampus during the encoding of emotional memories [60]. The amygdala is undoubtedly the neuroanatomical center of fear memory [58], with enormous influence on emotional learning and remembering of fearful events [61,62], and it has a role in memory processes that involve an emotional component [63]. The morphological complexity of the human basolateral amygdala, with the presence of numerous neuronal types, intranuclear dendritic bundles, and dendrodendritic contacts, implies its functional complexity [64]. The amygdala is the critical spot linked with Pavlovian fear response, i.e. unpleasant conditional response. This learned response is, in fact, more often than not an unpleasant sensation ranging from anxiety to expressed fear, while the neurobiological cause lies in the synaptic plasticity of amygdala neurons. It has been shown that excitatory memories of fear are formed in the amygdala, but that inhibitory extinction memories are formed simultaneously, capable of suppressing the expression of fear [65]. A balanced status of both is necessary for the normal functioning of individuals, but the aversive memories in the amygdala remain as a lasting but quiescent emotional trace [66]. Consequently, it is quite certain that the amygdala is the seat of aversive emotions. However, contrary to what was previously believed, the amygdala is not only the center of aversive emotions, but itself creates appetitive stimuli; moreover, the latter flow into it also from a variety of sources (anterior cingulate cortex, high-order sensory stimuli, thalamus, accumbens). Appetitive information of the amygdala is processed into the so-called Pavlovian approach behavior and there is evidence that the functionally dissociable amygdala subsystems are involved in associative processes underlying both appetitive and aversive emotional behavior [67,68]. All the above said should be taken to mean that there is hardly more fertile ground for the full influence of emotions and unconscious fears than behavior in intersexual relations. One of the possible reasons for the evolutionary enlargement and ever more complex emotional capacities of man might be sought in the morpho-psychological effects of concealed female genitals. Of course, besides being related with reproductive success, complex human emotionality has become the mediator of success or failure not only in relation to the opposite sex. Indeed, there are serious indications that the amygdala is an essential component of social cognition [69], this being important for successful interaction between the individual and the overall social environment. In general, emotions and memories are unbreakably linked, and the reason for that is simple: emotions are only purposeful if they are memorized. In the complex and tortuous male-female interactions, both influences, that of pleasant emotions or, contrariwise, that of unpleasant sensations (for example anxiety), are almost equally important. When recalled, fear memories mobilize an unpleasant and impressive, but eminently adaptive response [58]. Therefore, memorizing fear is a phylogenetic imperative. Fear must be committed to memory because it is one of the most effective methods for man to protect himself from the environment, and the amygdala is the place of remembering fear and the implicit emotional memory [61]. The emotional memory is the most complex, unpredictable, and almost impossible to control [57]. Why is this important for the matter being addressed? Because it is impossible to imagine intersexual relations without the presence of emotional contents, i.e. fear, anxiety, or uncertainty, which practically means without the amygdala, as well as the hippocampal formation and prefrontal cortex, since it has been shown that the hippocampus regulates activity in the prefrontal-amygdaloid fear circuit [58]. Of particular importance in male-female relations is the recognition of details and words encoded in aversive emotive context. More recent research into human behavior using functional magnetic resonance imaging (fMRI) indicated the location of these neural systems. It has been found that the location of memorizing aversive and neutral verbal stimuli encoded in an emotive context shows asymmetry and lateralization [70], thus indirectly confirming the presence of additional evolutionary instruments in this matter. On the other hand, appetitive sensations and pleasant feelings have a key role in intersexual relations, especially in the initial phase of the formation of a couple and in the maintenance of existing emotional relations between partners. The complex cognitive-emotional matrix of man contains a possibility for creating pleasant feelings, i.e. emotions, and, of course, for their memorizing. But it is in fact a double-edged sword of man’s psychology because precisely the conscious pursuit of events likely to create pleasant sensations in him and his favoring thereof is often conducive to trouble. This is not the case with animals, in which aversive reactions to unpleasant experience are more important, leading to restrictive and more cautious behavior. In contrast, man is often looking for events that will provoke agreeable sensations in him. The majority of people will opt for a behavior favoring pleasant sensations, whenever there is an opportunity, often consciously ignoring possible dangerous consequences. Of course, most sources of pleasant sensations are situated within the framework of intersexual relations, no matter whether it is the emotional state, sex act, actions preceding and following it, or those that may result from the success achieved in any other field. With respect to this, there is evidence of the role of endogenous opiates in emotional processes and belief regulation [71]. The quality of visual perception in intersexual relations is also very important, especially the emotional dimension. Bearing that in mind, a prominent amygdala activity in facial expressions and in the processing of body movement has been shown [72]. In recent years, numerous data have become available, supported by numerous fMRI experiments, leaving no reasonable doubt as to the existence of sex-related behavioral differences in the human brain. Sex differences in cognitive and emotional processes have thus been well documented. Women perform better in verbal and memory tasks, whereas men excel in spatial tasks [73–76]. Other evidence regards the important sex differences observed in affection and emotion processing [77]. Women perform better in speeded emotion-recognition tasks [78] and are more expressive [79]. There is a number of studies demonstrating gender specific changes in limbic energy utilization following emotional challenges [80] and gender differences in amygdala response following mood induction [81] and emotionally influenced memory. These results demonstrate a clear gender related lateralization of amygdala involvement in emotionally influenced memory, indicating that theories of the neurobiology of emotionally influenced memory must begin to account for the influence of gender [82]. Importantly, recent research has confirmed gender as being a critical variable in assessing biological responsiveness. Men and women can activate different limbic structures despite sharing a similar subjective experience [83]. The existence of these differences represents a contribution to the hypothesis on a morpho-psychological clue to the emotional and cognitive evolutionary matrix of man, because different psychological female and male reactions to the same or similar phenomena create conditions for increased intersexual tension, used by nature for reproduction in the first place, but also for the creation of material culture. Finally, comparing the basic differences between man and other mammals, an attempt to throw more light on the evolutionary reduction or “sacrificing” of the sense of smell, dominant in all other animals, seems inevitable. However, that reduction was followed by a pars pro toto important evolutionary compensation: important emotional structures developed near the primordial traces of the rhinencephalon, such as the basolateral amygdala, which, according to volumetric data, is enlarged in man more than in other primates [84, 85]. The human amygdala is enlarged compared with non-human amygdala, even when the general enlargement of the human brain is taken into account [86], along with the ability to process the complex emotions necessary for the strange survival model of man. In the complex cognitive-emotional and speech relations between woman and man, emotional memory is of special significance in the formation and preservation of a couple, since it represents the basis for positive feelings and affection for the partner, on the one hand, and the hostility and alienation of the couple, on the other. Darwin regarded emotions as a predisposition for adaptation. From Darwin’s prototypical evolutionary perspective, communication between individuals is the most important function of emotions [87]. Moreover, the central significance of communication lies in the existence of the sex-dimorphous emotional-cognitive and behavioral characteristics specific to woman and man, with the consequence of both understanding and misunderstanding between the sexes. Although opportune, both specific characteristics are crucial because they provide the neurobiological basis for intersexual tension, i.e. a guarantee of continual psycho-sexual interaction. In order for the propellant psycho-sexual manipulation to take place, a certain amount of misunderstanding between the sexes is necessary. As we know, there is no doubt that misunderstanding between the sexes is common experience. Regarding the issues of socialization and the sexual division of labor during human evolution, they have been treated from several aspects. One of the leading misconceptions is placing the woman in the context of subordination to the Paleolithic “Man the Hunter”, which has even served as the basis for certain modern attitudes about supposed gender inequalities. On the contrary, the absence of women hunters in these societies is taken as evidence that the sexual division of labor was an important precipitating factor in evolution, with the frequent superiority of women [88]. Importantly, there are anthropological data which point to the fact that the role of the human male was as crucial, and that it involved the decisive mechanisms aimed at optimizing tradeoffs between survivorship and reproductive effort [89]. Figure 1. Possible morpho-psychological cascade of human bipedalism. |
