Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.

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 Library of Excerpts

Female Centered Proto-Culture and Promiscuous Social Structures - Matrifocal Studies: Part 1


"Although this is a preliminary study, the evidence for synchrony and suppression of the menstrual cycle is quite strong, indicating that in humans there is some interpersonal physiological process which affects the menstrual cycle." (McClintock, M.K. (1971) Menstrual synchrony and suppression. Nature 229: pp. 245)

“All combinations of male tactics from rape (Shields and Shields 1983, Thornhill and Thornhill 1983) to high investment (Trivers 1972) and the environmental and social circumstances that occasion their expression have received analysis in the literature. As Hrdy (1981) observed: “The sociobiological literature stresses the travails of males--their quest for different females, the burdens of intrasexual competition, the entire biological infrastructure for the double standard. No doubt this perspective has led to insights concerning male sexuality. But it has also effectively blocked progress toward understanding female sexuality--defined here as the readiness of a female to engage in sexual activity.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 602)

“This context for human sperm competition almost certainly exceeds all others in importance. Female extramarital sex occurs in 73.2% of indexed societies and is common in 57.1% (Fig 1I). The cross-cultural occurrence of male and female extra-marital sex is surprisingly similar (Fig 1J). Gaulin and Schlegel (1980) found low levels of paternity assurance in nearly half (N=61) of the 135 societies they examined. Presumably, sperm competition is especially intense in these societies. Kinsey et al. (1953) found ca. 26% of U.S. adult females had engaged in extra-marital intercourse, and over 50% of respondents in the Cosmopolitan survey (Wolfe 1981) indicated that they had had extramarital liaisons. Although similar data are not available for other cultures, it seems safe to assume that female extra-bond sex occurs in all but the most restrictive societies, and that it is common.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 609)

“In many cultures, however, choice of the first primary mate for a girl is made entirely by the parents and often exclusively by the daughter’s male parent (Levi-Strauss 1969), Daly and Wilson 1978, Symons 1979). The parents’ interests may, but probably will not be coincident with the daughter’s. Thus a parent-offspring conflict (see Trivers 1974) is created that may result in extramarital adventures by dissatisfied daughters.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 611)

“Chimpanzees are reproductively extraordinary among the great apes. They are not strikingly dimorphic for size as are the other two species (Fig 2), but male chimpanzees have enormous scrotal testes, proportionately about 5 and 10 times larger than Pongo and Gorilla, respectively, and a specialized penis more than twice as long as that on the much larger gorilla. Short (1981) has calculated that the testes of an average chimpanzee can sustain sperm production at a level that will produce at least four full-strength ejaculates/day, each containing several times the number of sperm in an average gorilla or orangutan ejaculate.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 619)

“Masturbation seems a bizarre, maladaptive behavior because it wastes sperm, but the practice is almost universal among U.S. males and is particularly common in adolescents (Kinsey et al. 1948, Sorensen 1973). Masturbation is also commonly observed in some captive primates. It has been said that “primates masturbate, because they can,” but if autoeroticism were maladaptive, the tendency should have been repressed by natural selection. A clue to a possible function is found in the fact that males who do not ejaculate by coitus or masturbation for some period of time experience nocturnal emissions, i.e. spontaneous seminal discharge during sleep. This suggests that stored sperm and/or accessory gland products may have definite “shelf life” after which they are best discarded and replaced with new in order to stay competitive. Another possibility that has not been properly investigated is that frequent ejaculation may activate some feedback machanism (e.g. testosterone/inhibit) to stimulate higher levels of spermatogenesis and accessory gland secretion.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 633)

“Homo sapiens sapiens appeared sometime between 50,000 and 100,000 years BP, and was characterized by loss of robustness and changes in the female pelvis. The female skeletal changes are indicative of some change in pregnancy and births. These alternations may have included reduction in the gestation period from 11 months to the present 9 months and a concomitant increase in dependency of infants on parental care. The prediction is made on the basis of morphometric comparisons with the great apes and other mammal (Pilbeam 1984).” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 633)

“Consortship would have gradually given way to long-term pairbonding with progressively higher levels of male investment in mates and offspring. Increased male investment coincided with the increased levels of paternity assurance that resulted from improved male efficiencies in controlling their mates’ reproductive activities. Selection strongly favored sexually jealous males who maintained tight control over their mates, and this progressively and substantially reduced the levels of sperm competition. Females evolved cryptic ovulation, perennial pendulous breasts, and behavioral deceptions to militate against male control efficiencies, and to achieve reproductive and other advantages from faculative polyandry. Paradoxically, female opportunity to secure advantages by faculative polyandry was created and propagated by the ability of males to mix high and low investment strategies.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 651)

“An excessively large penis produced by epigamic selection would be no less effective in delivering sperm than one of optimal length, but a substantially shorter (than optimal) penis would obviously place its owner’s ejaculates at a disadvantage in competition with those deposited by a longer organ. Therefore it may be possible to test some predictions of the ejaculate delivery/sperm competition hypothesis for human penis length and distinguish this function from one of display.” (Robert L. Smith (1984) Human Sperm Competition. in Sperm Competition and the Evolution of Animal Mating Systems pp. 631)

“Testes Size Although we were unable to predict the magnitude of testes size increase, our predictions were qualitively correct. Testes size increased with body size and the relationship was negatively allometric. For their body size, “genera” in which females are likely to mate with more than one male during estrus have larger testes than those where only one male usually gains access. The hypothesis that sperm competition is important in the correlation between breeding system and testes size requires that multi-male primates, as well as having larger testes, have higher rates of sperm production than single-male or monogamous species. In other words, we need to show that the larger RTS is not merely due to an increase in non-spermatogenic tissue. If the value of the seminiferous tubules is applied as a measure of potential sperm production, our hypothesis is supported. Chimpanzees, baboons, and macaques (Macaca spp.), all with multimale breeding systems, have ratios of tubules to connective tissue in their testes that range from 2.2:1 to 2.8:1; while man, gibbons (Hylobates spp.), and langurs (Presbytis spp.), which are not multi-male have ratios of 0.9:1 to 1.3:1. In addition, the sperm production rate of the rhesus macaque (Maccaca mulatta) is about 23 x 106, while the corresponding value for man in only 4.4 x 106 (Amann et al., 1976, Amann and Howards 1980). These data suggest that multi-male species not only have larger testes but also have a higher sperm production capacity per unit weight of testis tissue. Our measure of RTS may, therefore, underestimate the effects of sperm competition as a selective force increasing sperm production rates. Nevertheless, sperm production is unlikely to be the only reason for differences in RTS among primates. For example, seasonality of breeding could be an important factor; species with a short breeding season and hence periods of intense copulatory activity may need larger testes. Certainly, the multi-male genus Macaca which contains predominantly seasonal breeders has the largest RTS. In this connection, it is interesting to note that the single-male “genera” do not have larger RTS than monogamous primates (on average it is rather less), and sperm production does not, therefore, seem to relate to the number to females that a male serves during the year. As with all comparative studies, aberrant taxa are revealed. Saguinus oedipus has rather larger testes for its body size and a monogamous breeding system; likewise for the Hamadryas baboon with its single-male breeding system. Nevertheless, this study reveals a consistent trend and emphasizes the need for similar studies on other mammalian groups. Among primates, further progress will require studies on the fine structure of primate testes, on sperm production rates and on copulation frequencies and timing in natural populations. Even then, controlled experiments using genetic markers will be necessary to validate correlative evidence. Intrasexual Selection and Sperm Competition Recent surveys of sexual selection (e.g. Halliday 1978) restrict themselves to the traditional distinction made between intra sexual and epigamic selection for access to mates. This chapter has so far considered one component of post copulatory intrasexual selection, sperm competition (Short 1977). Epigamic selection concerning active female choice on the male phenotype develop sexual swellings when they are in estrus. It is generally accepted that these serve to attract males. These species, with one exception, live in multi-male troops and whether sexual swellings are associated with active choice in male (epigamic selection) or passive “choice” (provoking inter-male conflict so that the dominant male achieves access to the female or where males from neighboring troops are enticed to compete with resident males for access) is not known. However, recent comparative studies on primates have indicated a strong influence of intrasexual selection on both sexual dimorphism in body size (Harvey et al. 1978).” (Harvery PH & Harcourt AH (1984) Sperm Competition, Testes Size, and Breeding Systems in Primates. in Sperm Competition and the Evolution of Animal Mating Systems pp. 595-6)

"Roger Short...had predicted that in {primate} species where females mate with more than one male during a reproductive cycle, the males would have larger testes for their body size than in species whose females had only a single mate per cycle. When the females were promiscuous, the sperm of each male would have to compete with those of other males, and the male producing the most sperm was most likely to generate offspring. [quote from] (Harvey and Clutton-Brock 1983, p. 315" (Cronin, Helena (1992) The Ant and the Peacock: Cambridge Univ. Press, Cambridge p. 97)

"Most often, female primates have several males to interact with and choose from, and they most often take advantage of the situation. In groups with multiple males, such as baboons, macaques, and many other primates, females most often copulate with more than one male, and sometimes several in rapid succession. This situation is most apparent in species with breeding seasons, so that several females are in estrus at the same time and no single male can sequester even one female all for himself. Promiscuity, or mating with every possible male, occurs most often when females cycle synchronously. Contrary to what theory suggests, these female primates are not selective and mate with more than one male even when ovulation is imminent." (Small, Meredith F. (1993) Female choices: Sexual behavior of female primates. Cornell Univ. Press, Ithaca, 1993 pp. 135)

"In so far as there is differential expression of the gene in the two sexes it will be subject to sexual selection, i.e., the effects of different criteria, or timing, of mate choice in the two sexes. Such selective influences will determine the range of variation maintained separately in the populations of males and females. These in turn will exert their effects through actions on the rate and degree of lateralization. Thus the sex difference in the rate of maturation may be secondary to the fact that mate choice (for optimal features of the species characteristic of language) occurs at a later age in males than females (males are one to two years older than females at the time of marriage a difference that is consistent across cultures." (Crow TJ, Crow LR, Done DJ, Leask S (1998) Relative hand skill predicts academic ability: global deficits at the point of hemispheric indecision. Neuropsychologia : )

"Edward Westermarck in his early classic A Short History of Marriage (1968: 126-155) discussed consent as a condition for marriage. Females, he noted, most often were married off at the will of some male-father, family elders, uncle. It is to be noted that the male partner in such marriages, also, had little personal choice. However, Westermarck pointed out that females in the simplest hunting and gathering societies could - and did - refuse the assigned mate. Sometimes she could do this directly and in other societies by subtle, indirect action. She lost much of this freedom in technologically more advanced societies. Some of the strongest arguments against male dominant choice of females as sex partners can be found in the statistical, cross-cultural work of George Murdock (1949: 20-21). Out of 241 societies where his criteria could be applied, 163 involved some consideration: bride-price, bride service, or exchange of women. In other words, families made the decisions rather than the individuals involved. Regarding divorce, Murdock (1969: 175-76) found, somewhat surprisingly, that in thirty of forty societies there were no substantial differences in the rights of men and women to terminate a marriage. Only 15 percent actually had the stereotyped view where men controlled the action. If divorce involved equal female choice, isn't it likely that she would have had much to say about the original marriage? Further analysis of mating practices in primitive society raises more questions as to male choice selecting for specific traits. Murdock's worldwide sample of 25o societies (1949:263) showed that only three had a generalized sex taboo. Most of the others allowed premarital sex, extra-marital sex, wife-lending, etc., all of which could be involved in pregnancy with someone other than the social father." (Smith, James M. (1976) Sexual selection in recent human populations. California Anthropologist 6 (1): pp. 20)

"Overall, females apparently were choosing males who were sociable, cooperative, willing to share, and protective. In general, then, sexual intercourse would not be disruptive of either ongoing group interaction or organizational flexibility. Mothers obtained plant food from their own efforts, protein from a variety of sources (insects, plant protein, and some meat form their own efforts, and additional meat from males); had their own tools for protection; and had durable social bonds with sons, daughters, brothers, and sisters who shared the food quest and assisted in protective functions. Thus permanent mates to provide food and protection would be neither necessary nor particularly advantageous. Sexual preference was, however, getting easier to communicate, and it is likely that many australopithecines did have preferred sex partners." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 210)

"These studies suggest that prior evolutionary accounts have emphasized too strongly intrasexual mate competition as primarily a male activity. For these samples, at least, such competition appears to occupy women as much as men. Indeed, summing across all 23 tactics, there was no sex difference in overall performance frequency. Female-female competition appears to be an unnecessarily neglected area of research in social psychology and evolutionary biology (see Cunningham, 1986). Similarity exists strongly for the acts considered to be most effective. The acts frequently performed and considered highly effective for both sexes involve displaying sympathy, kindness, good manners, helpfulness, and humor. Since the characteristic kind-understanding emerges at or near the top of mate selection preferences for both sexes (Buss, 1985; Buss & Barnes, 1986), these results support the general hypothesis that mate selection criteria influence tactics of intrasexual mate competition, even for criteria that show no sex differences." (Buss, D.M. (1988) The evolution of human intrasexual competition: tactics of mate attraction. Journal Personality and Social Psychology 54 (4): pp. 625)


"Although measurements of testis size by orchidometry in living subjects are difficult to standardize, they suggest smaller testes in Japanese and Korean men than in Caucasions. Weighing at autopsy is more accurate and showed that the size was twofold lower in two Chinese samples compared with a Danish sample. Differences in body size make only a slight contribution to these values." (Diamond, JM (1986) Variation in human testis size. Nature (London) 320: 488) [note: larger African testes supports promiscuous origins hypothesis, yet if African testosterone levels are higher, it refutes inverse relationship between sperm and T production]

"The differences in dizygotic twin frequency, and presumably ovulation rate, are in the same direction as the differences in testis size. The frequencies of dizygotic twins are even higher (up to 49 per 1,000 births) among African blacks. ... Yoruba women, with the world's highest frequency of dizygotic twins, have higher FSH and LH levels at the time of ovulation than do Japanese women, who have the lowest frequency of dizygotic twins. This variation in female hormone levels may contribute to the distribution of the incidence of breast cancer, which is known to be related to oestrogen levels. Even after all other risk factors for breast cancer have been taken into account, the incidence among Japanese women remains inexplicably low. Perhaps this puzzle, the so-called 'Japanese factor' of (breast cancer, is related to the low double-ovulation frequencies and low hormone levels." Diamond, JM (1986) Variation in human testis size. Nature (London) 320: 488-489)

"One characteristic among primates has been clearly targeted for possible selection by Fisherian female choice--male penis size. Primate males living in groups with many females and many males, groups in which promiscuity is the mating rule, have long penes (Dixon 1978). Male chimps, in fact, use their penes for display toward estruous females. Because a longer penis would give a female pleasure (note that the human male has the longest and thickest penis of any primate), female choice might have been a factor driving penis length to extremes among primates." (Small, Meredith F. (1993) Female choices: Sexual behavior of female primates. Cornell Univ. Press, Ithaca, 1993 pp. 109)

"These studies suggest that prior evolutionary accounts have emphasized too strongly intrasexual mate competition as primarily a male activity. For these samples, at least, such competition appears to occupy women as much as men. Indeed, summing across all 23 tactics, there was no sex difference in overall performance frequency. Female-female competition appears to be an unnecessarily neglected area of research in social psychology and evolutionary biology (see Cunningham, 1986). Similarity exists strongly for the acts considered to be most effective. The acts frequently performed and considered highly effective for both sexes involve displaying sympathy, kindness, good manners, helpfulness, and humor. Since the characteristic kind-understanding emerges at or near the top of mate selection preferences for both sexes (Buss, 1985; Buss & Barnes, 1986), these results support the general hypothesis that mate selection criteria influence tactics of intrasexual mate competition, even for criteria that show no sex differences." (Buss, D.M. (1988) The evolution of human intrasexual competition: tactics of mate attraction. Journal Personality and Social Psychology 54 (4): pp. 625)

"...in the chimpanzee, several males mate frequently with the oestroud females, so that each male has to deposit enough sperm to compete with the presence of sperm form other males. For the chimpanzee, therefore, we hypothesize that selection will favour the male that can deposit the largest number of sperm; thus the volume of spermatogenic tissue and hence the testis size is far greater in the chimpanzee than in the gorilla or orangutan. If this is correct, it implies that primates in which more than one male mates with each oestrous female should have larger testes relative to their body weight than those which single-male breeding systems. We have tested this prediction across a wide range of primates, and the results support the hypothesis. The relative size of testes may, therefore, provide a valuable clue to the breeding system of a primate species." (Harcourt AH, Harvey PH, Larson SG, Short RV (1981) Testis weight body weight and breeding system in primates. Nature 293: pp. 55)

"Adult australopithecine males would have had stronger social bonds with adult females, especially but not exclusively with their mothers and sisters, than is true for living chimpanzees. There was an even longer and more intense association with the mother and with siblings than for ancestral and transitional populations. Further incorporation of adult males into group life was made possible by increased sociability and decreased disruptiveness of the males (related both to the longer period of maternal care and socialization and to the probable decrease in sexual dimorphism, particularly in canine height). This relatively relaxed incorporation of males into the group was perhaps also reinforced by male contributions to defence and meat acquisition and by male help in bringing raw materials for tool manufacture from some distance to the campsite." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 219)

"Overall, females apparently were choosing males who were sociable, cooperative, willing to share, and protective. In general, then, sexual intercourse would not be disruptive of either ongoing group interaction or organizational flexibility. Mothers obtained plant food from their own efforts, protein from a variety of sources (insects, plant protein, and some meat form their own efforts, and additional meat from males); had their own tools for protection; and had durable social bonds with sons, daughters, brothers, and sisters who shared the food quest and assisted in protective functions. Thus permanent mates to provide food and protection would be neither necessary nor particularly advantageous. Sexual preference was, however, getting easier to communicate, and it is likely that many australopithecines did have preferred sex partners." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 210)

"We do not know why men have conspicuous genitals, but a male chimp solicits a female by opening his legs, displaying an erect penis and flicking his phallus with a finger as he gazes at a potential partner. A prominent, distinctive penis helps broadcast one's individuality and sexual vigor, which may lure female friends. In many species of insects and primates, males have exceptionally elaborate penises, and scientists think these evolved specifically because females chose those males with elaborate, sexually stimulating genitals. So perhaps as Lucy's ancestors became bipedal some four million years ago, males began to parade their genitals in order to make special friends with favored females--selecting for those with large organs." (Fisher, H. (1992) Anatomy of Love: The Mysteries of Mating, Marriage, and Why We Stray. Simon & Schuster, New York, 1992. pp. 177)

[citations removed] "But why did these early pair-bonds need to be permanent? Perhaps like foxes and robins, our ancestors only needed to form pair-bonds long enough to rear their young through infancy. what made me think of this was a remarkable correlation between the length of human infancy in traditional societies, about four years, and the length of many marriages, about four years. Among the traditional !Kung, mothers hold their infants near their skin, breast-feed regularly through the day and night, nurse on demand, and offer their breasts as pacifiers. As a result of this constant body contact and nipple stimulation, as well as high levels of exercise and a low-fat diet, ovulation is suppressed and the ability to become pregnant is postponed for about three years. Hence !Kung births are about four years apart. Four years is the usual period between successive births among continually breast-feeding Australian aborigines and the Gainj of New Guinea. Infants are generally also weaned around the fourth year among the Yanomamo of Amazonia, the Netsilik Eskimos, the Lepcha of Sikkim, and the Dani of New Guinea. Although birth spacing varies among populations of hunter-gatherers, and maternal age and number of children previously born to a woman affect birth intervals, these data have led anthropologist Jame Lancaster and others to conclude that a four-year pattern of continual nursing through the day and night--was the regular pattern of birth spacing during our long evolutionary past. Thus the modern worldwide divorce peak--about four years--conforms to the traditional period between human successive births--four years. So here is my theory. Like pair-bonding in foxes, robins, and many other species that mate only through a breeding season, human pair-bonds originally evolved to last only long enough to raise a single dependent child through infancy, the first four years, unless a second infant was conceived." (Fisher, H. (1992) Anatomy of Love: The Mysteries of Mating, Marriage, and Why We Stray. Simon & Schuster, New York, 1992. pp. 153-4)

"Although some food and protection were supplied by males, sexual partners were only occasionally and irregularly involved; brothers and sons who frequently associated with mothers and sisters probably were the males who most regularly contributed animal protein and protection." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 163)

"The more intelligent transitional female (remember, it is her offspring who will be most likely to survive) could use her intelligence to select males for copulation. In other words, increases in intelligence and a richer, more sophisticated communicatory repertoire mean the mating system itself could become more complex. I hypothesize that the mating system was changing so as regularly to include female discrimination and choice of sex partners in terms of a number of characteristics. Females probably had sex more frequently with those males who were around often, playing with offspring, helping in protection, occasionally sharing meat and foraged plants, and who were generally friendly. With females choosing the less disruptive males, there also would be less likelihood that males having sex with mothers might accidentally injure offspring. To the extent that the ability to learn to be more sociable has been enhanced by genetic changes that have augmented our human potential --- and this is a subject about which little is known --- sexual selection in the hominid divergence also could have increased the capacity of males for relaxed social interaction. ... What may have been selected for among the transitional hominid males was the capacity to be extremely social but yet sufficiently aggressive when required and an ability to make fine discriminations as to situational necessity. Thus, the males of the transitional population would come to more closely resemble the females than had the males of the ancestral population. ... Much of the selection pressure engendered by female choice of sexual partners was directed toward male social and communicatory behavior, reinforcing the potential and capacity for sociability, social learning, and intelligence." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 164-5)

"Heightened maternal investment resulted, in turn, in increased sexual selection by females. Natural and sexual selection reinforced each other during the transition. Selective pressures were intense, and evolutionary change may well have been extraordinarily rapid." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 167)

"The measure of natural selection is reproductive success (Dobzhansky, 1970). The crux of the matter is how many offspring survive for any given female or male, rather than the number of copulations or number of infants born per se. Transitional hominid fathers, like the ancestral population before them, would not know their young and so could not effect the specific survival chances of their own progeny as differentiated from other young of the community." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 161)

"Considerable discussion has centered on the question of whether a gestural language of a vocal language evolved first. The proponents of a gestural language note that considerable nonvocal communication occurs among apes (Hewes, 1973a, b), and experiments indicate that chimpanzees can be taught elements of human sign language (Gardner and Gardner, 1972) but not to speak (Hayes, 1951; Hayes and Nissan, 1971). On the other side, Washburn and Strum (1972) and Washburn (1973) have pointed out that the essential character of human vocally based language is that it is a system whereby, through the recombination of a limited number to arbitrary elements (phonemes), it is possible to produce vocal signs for a potentially endelss variety of meanings." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 127)

"A more likely alternative is that females did more and more direct initiation of sexual activity --- by overtly soliciting intercourse and by nonverbally signaling receptivity (Figure 7:8). Morphological changes were replaced with other forms of communication where females through degree of physical spacing and type of gesture, facial expression, eye contact, posture, vocalization, and other nonverbal behavior signaled to males that they were willing --- or unwilling --- to engage in sexual intercourse. The loss of estrus then can mean that a female can initiate sex with males at any time. But it can also mean that she may choose not to mate, even when her hormones are such that she could become pregnant." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 154)

"Social and physical context also affect food from another chimpanzee, in which case it has been referred to as "begging." Alternatively, it may evoke a tactile social response that we would describe as "comforting"; in the latter instance the outstretched hand has been described as indicating a request for "reassurance" (Goodall, 1972). Among the transitional population it is reasonable to suppose that a wide repertoire of nonverbal communicatory elements, including context, was used; selection would be for a communication system in which a more complex brain made it possible for various in-context combinations of body movements plus some vocal components to convey more complicated social and environmental information than could the ancestral population. It is therefore possible that some of the requisite mental abilities for the later development of speech as we know it were already evolving at the time of the transitional hominids." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 156)

"The use of quite complex nonverbal communication "about something" in highly social settings has been illustrated by laboratory observations of sexual interaction among three pygmy chimpanzees (Savage-Rumbaugh et al., 1977). Eye contact and facial expression are used to indicate interest in sexual engagement. Further, many body movements and gestures precede copulation. Pygmy chimpanzees use a wide variety of positions for copulation, and some mutual agreement as to position must be reached if they are to actually engage in sex. Many of their movements and nearly all the gestures observed by these pygmy chimpanzees prior to intercourse seem to concern copulatory position (Figure 6:5). Especially interesting is the fact that the movements and gestures used in these sociosexual contexts range from very explicit ones, such as one animal trying to turn the other around or the other actually moving to her preferred position, to purely iconic gestures in which a desired or agreed on position is simply indicated gesturally. Here then, in these sociosexual contexts, an integration of a variety of communicatory modes is exhibited --- eye contact, facial expression, body movement and position, and hand gestures. Included are gestures that are iconic, and that can perhaps be considered "presymbolic" forms of communication. These observations of pygmy chimpanzees; sociosexual communication provide a particularly clear-cut example of the sort of integrated communicatory capacities that, if they existed in the ancestral population, would have provided a firm foundation for the evolution of the human communicatory system." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 122)

Quote from Tutin, 1975: 448 in Tanner "As previously mentioned, female cooperation is essential for the maintenance of these special relationships and they thus present an opportunity for females to exercise choice. If female choice is involved, it is of interest to note that the selection criteria appear to be social and caretaking abilities of the males and not their dominance status." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 97)

"Another part of the story, speculative but crucial, concerns the highly impressionable state of human infants, the males of whom seem to have developed a sexual liking for "maternal" females --- females that reminded them of their nursing mothers. Sexual imprinting, in which the young memorize features of their parents, and then seek out those features in mates when they mature, is prevalent in animals." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 96)

"If early, impressionable human infants imprinted on their nursing mothers, males would have grown up with a confusing lust for women who were not ovulating, but lactating. Genetically disadvantageous to males, this confusion would have been a genetic advantage to females who, sexually attractive almost all season round, stood a better chance of keeping fathers to help with children." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 97)

"But effective clitoral stimulation, though intensely pleasurable, does not necessarily occur during sexual intercourse. Female pleasure, for more than male pleasure, is a function of erotic learning and cultural expectations. Among human societies the most advanced orgasmically are purported to be the women of Mangaia, a southern Cook Island in central Polynesia. Mangaian females reach orgasm two or three times during intercourse. Upon entering puberty at thirteen or fourteen years of age, Mangaian boys go through a series of initiation rites into adulthood. Part of the initiation includes being instructed in methods of stimulating women to maximum sexual pleasure. Indeed, Mangaian women are expected to attain orgasm during intercourse each time; if not, the Magnaian man who fails to please her loses his status in the island's society. Two weeks after a manhood initiation ritual involving penile mutilation, an experienced older women begins to practice boys in the arts of conferring female sexual pleasure. According to their ethnographer, D.S. Marshall, Mangaians probably know more about female anatomy than most European physicians. The Mangaians, with no semblance of a Puritan heritage, do not consider female sexual pleasure an indulgence. They consider it a necessity. High cultural expectations for female orgasm have led to high rates of female orgasm." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 62)

"Different prehuman species suggest different levels of sperm competition. Judging from its teeth, Australopithecus africanus was certainly a vegetarian. Like gorillas, the vegetarian australopithecines showed a bigger difference in body size between sexes than men and women do today, suggesting that they were sperm-competition avoiders. Although no one, of course, knows for sure, Robert Smith speculates that physically imposing males bossed relatively sexually faithful females in australopithecine harems. These ancestors would have been very sexist, but the males, violently intolerant of promiscuity, would not have developed large genitals. This sultanlike breeding behavior could well have undergone radical change with the evolution of Homo habilis, "handy man": Smith postulates that subordinate habilis males, scavenging meat and offering pieces of it in exchange for sex, upset the earlier breeding system. The cooperative hunting groups that began with Homo erectus --- our most recent evolutionary predecessor --- ushered in relatively high levels of sperm competition. Homo erectus males were not much larger than Homo erectus females. Homo erectus was a communal species who not only gathered edible plants but hunted mammoths and used fire. Eating and sleeping together in groups --- the sort of cooperative groups needed to hunt --- may have made them far more social, more talkative, and better barterers than their sexually dimorphic australopithecine ancestors. And more promiscuous. It was with Homo erectus, Smith suggests, that people developed their relatively large male genitals." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 51)

"Considerable female promiscuity may have been our immediate primate heritage." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 48)

"Rampant female mating leads to competition not before but after copulation, not among bodies but among sperm. A female copulates with several males whose sperm compete to fertilize her. Sperm competition can occur even if a female copulates with different males several days apart. This is because sperm are hardy and may survive in the vagina of a chimpanzee or woman for as long as eight or nine days. Any female who copulates with more than a single male while ovulating opens the gates to a sperm race. The males or men who produce the sperm are not direct entrants; they are more like corporate sponsors advertising their name and providing financial backing. Not all participants in the all-male marathon are equally prepared to win. Mammals who mate more frequently, and produce more sperm per ejaculation, are more likely to impregnate their partners. Favoring the sperm of one male over that of competitors are such things as position during intercourse, force and timing of pervic thrusting, number and speed to ejaculated sperm, and proximity of the spermatic means of delivery---the penis---to the egg at time of ejaculation. Copious sperm production (estimated by testicle weight), deep penetration, and an elongated penis are all presumably advantages to males engaged in sperm competition. Perhaps most important is sheer sexual vigor, with more active males ejaculating the greatest number of times gaining a competitive edge. The charm and proficiency of a male---his ability to seduce a female and to continue to please after seducing her---of course also crucially determine his chances of entering and therefore of winning the competition; and in this sense females make the great impact of generally deciding who will and will not compete. There is also evidence that a woman who climaxes while making love to her lover is more likely to become pregnant by him." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 37)

"Large testes and big penises are advantages only under conditions of widespread sexual promiscuity. Among our closest relatives the great apes, only male chimpanzees have testicles more prodigious than those of men. And chimps, with their big, heavy testicles, are more sexually promiscuous than humans. that the sperm-producing organs of chimps and humans are relatively big and heavy strongly suggests that some of our not-so-distant hominid ancestors were far more promiscuous than gorillas and orangutans --- or than many people are today. In the evolutionary past, the competition to reach primate eggs was sometimes between sperm from different male donors. If two or more males copulated with the same female within a period of days, an advantage in begetting offspring accrued to the one who ejaculated the greatest quantity of vigorous sperm cells. Like an auto race won by the driver whose sponsoring company can afford to provide him with the most souped-up car, the male with the best-timed copulation, most far-reaching ejaculation, and biggest testicular "engine" able to produce the greatest quantity of sperm tended to win the "game" of impregnation. souped-up genitals with a lot of spermatic firepower, like incredibly expensive streamlined racing cars, are worth it only if there is some sort of race or contest. Otherwise they seem expensive." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 33)

"Pan paniscus shows increase female receptivity, variability in copulatory position, male or female initiation of sexual behavior, differential male and female preferences for copulatory position, and association of food sharing and sexual behavior. Their sexual behavior appears to function in proximate terms as a tension-reduction mechanism. Lowered tension, in turn, facilitates multi-male, multi-female social groups. Lowered levels of aggression and increased sexual activity appear to be associated with paedomorphism, and the behavioral and anatomical/physiological characteristics of the species appear to be a consequence of a feeding ecology that promotes large groupings of the animals at preferential and comparatively rich feeding sites." (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 702)

"A second reported difference is that males or females may initiate copulatory behavior among the bonobos, whereas only males initiate it among chimpanzees (Savage-Rumbaugh and Wilkerson 1978). A third difference, noted by several observers (Kano and Mulavwa 1984; Kuroda 1984; Thompson-Handler, Malenky, and Badrian 1984), is that food sharing between males and females and among females tends to occur in the same context as sexual behavior, associated with excitement and tension." (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 703)

"Chimpanzees are reported to share food in two types of situations. Mothers sometimes share food with their infants (McGrew 1979), and meat---a prized food item---may be shared among adult males and females (Teleki 1973; Goodall 1986). Recent observations in the Ivory Coast (Boesch and Boesch 1989) indicate that sharing of meat by forest chimpanzees occurs several times more often than among savanna chimpanzees. Increased sharing among forest chimpanzees makes them more like bonobos, who occupy a similar environment. Bonobos, however, share food items other than meat (Badrian and Badrian 1984; Kano 1980; kuroda 1980, 1984; de Waal 1987). Sharing of food is a common phenomenon, and it occurs even when food is plentiful and when an individual already has some in his or her possession. (Badrian and Badrian 1984; Kuroda 1984). Moreover, and unlike chimpanzees, bonobo sharing food is associated with sexual behavior (Jordon 1977; Savage-Rumbaugh and Wilkerson 1978; Kano 1980; Kuroda 1980,1984; Thompson-Handler, Malenky, and Bodrian 1984; de Waal 1987). The co-occurrence of food sharing and sexual behavior among Pan paniscus appears to be structured by the social characteristics of the animals and by the type of food. Males rarely share with other males (unlike chimpanzees). Females share with other females, most often in the context of one female approaching another to beg for food and soliciting genito-genital contact and rubbing (Kuroda 1984). Badrian and Badrian (1984) also observed that genito-genital rubbing occurred most often at feeding sessions and soon before or after one of the females had been involved in heterosexual mating. Sexual interaction over food most commonly occurs, however, when females approach dominant males to take or beg for food. Dominant males are the most likely to be in the richest part of the feeding area and to have prized foods, and they are the most likely to be approached by females. Kuroda (1984) observed that females approach males to beg for food without apparent hesitation and that they are more likely to be successful in obtaining food if they first copulate with the males. The behavior of bonobo females suggest that sexual receptivity may be a device to get access to food, and they have been reported to behave in that way (Badrian and Malenky 1984). (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 705-6)

Since maternal investment in the developing fetus is principally in the form of nutrients, it is not surprising that recent research has shown that it is the level of such nutrients stored in the mother's body - fat, in other words - which is critical to fertility. This finding explains why the age of menarche (the point at which a young women begins to menstruate) has dropped progressively with rises in living standards in general and nutrition in particular, from an average of 15.5 years a century ago in the USA to one of 12.6 years today. It also explains why body weight, rather than other indicators such as height, appears to be the critical factor. Body fat increases prior to menarche by a factor of 120 percent and in so doing reaches a critical level of 24 percent by weight at the onset of sexual cycling. However, early sexual cycles tend to be infertile and irregular, and a further increase in body fat proportion to a typical 28 percent is achieved by age eighteen, at which point full fertility is normally achieved. So sensitive is the female body to body weight variations that some women athletes can turn their sexual cycles on and off at will with just a three-pound change in weight. " (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell. pp. 161)

"This suggests that even if female choice alone were driving encephalization in our ancestors (which I don't believe was the case) modern males and females would still be expected to have very similar brain sizes and mental abilities. This is because dimorphism in brain size evolves very slowly whereas encephalization evolved very rapidly. The lack of sexual dimorphism in modern human brain size is therefore not a strong argument against the hypothesis that human mental evolution was driven by selective mate choice." (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 116)

"Where interactions between a man's own children are concerned, he and his wife's brother will be in agreement if they are indeed his own; both will favor sacrifice wherever benefit exceeds cost. However, if his paternity is uncertain, his degree of agreement with his wife's brother will decline in direct proportion to the degree of uncertainty involved, and will fall towards that which the offspring themselves will favor when uncertainty of paternity reaches the critical, approximately one-quarter level at which mother's brothers should begin to become significant figures." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell.pp. 214)

"...because common observation of our own societies shows that where divorce and remarriage are common, it is links with maternal kin which tend to be preserved, and it is often the child-mother and brother-sister ties in particular which are most important." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell.pp. 213)

"The consequence of all this is that if a man's certainty that his wife's offspring are indeed his own drops below a certain, critical value, his ultimate reproductive success may be promoted by some degree of investment on his part, not in his wife's offspring - who may or may not be his - but in his sister's. This is because maternity, as opposed to paternity, is always certain in the same sense that a child is physically part of its mother and issues from her in an unmistakable way." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell.pp. 212)

"...because common observation of our own societies shows that where divorce and remarriage are common, it is links with maternal kin which tend to be preserved, and it is often the child-mother and brother-sister ties in particular which are most important." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell.pp. 213)

But such paedomorphic trend could be explained if we could somehow show that it was part and parcel of the overall process of female choice for hunting skills. In fact, this is easier than it seems, because there are good reasons for believing that it would have been young, rather than mature, male hominids who first began to hunt. Experiments in which a colony of monkeys living near a beach were fed first with potatoes and then with rice left on the sand showed that it was a young member of the group who first discovered how to wash the food (as it happens, a female) and that the readiness to adopt this practice varied directly with age, younger individuals being more ready to take it up than older one. In the second place, it seems likely that younger, unmated males, probably associating in loose "all-male groups." would have been much better placed to undertake what must have been cooperative hunts than were older males encumbered with females and young who could not be left unguarded while their "owner" ran off chasing game. If hominid females with a taste for meat were prepared to reward younger, meat-giving hunters with matings, the reproductive success of such younger males would rise relative to that of older ones. This in itself could favor paedomorphosis by way of selection for youth, but it would also have set the scene for the other inevitable consequence of a meat-eating economy, in which greatly increased male parental investment could enable the gradual evolution of more retarded, paedomorphic infants." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell.pp. 186)

"...whereas women have about one quarter of their body weight in the form of fat, men on average have only about half that amount. In other words, although women on average have about twice as much fat as men, they nevertheless weigh on average almost a quarter less than men.....When we observe that in women the degree of fat deposits is critical to reproductive success in primal conditions, but that in men muscle, bone, and height are critical in aggressive encounters with other men..." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell. pp. 144)

"...the vast majority of human societies, approximately 84 percent of the total, are either generally polygynous or allow polygyny to those men wealthy or powerful enough to be able to practice it. Indeed, looked at from this point of view, one could argue persuasively that polygyny is the mating strategy characteristic of our species and that the remaining human societies which are mostly monogamous (with less 1 percent polyandrous), represent a subordinate, minority trend in human mating systems." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell. pp. 132)

"Mating strategies can be classified in terms of the number and sex of the individuals concerned: we can have uni-female, multi-female, uni-male, and multi-male units combined in four possible ways. In a multi-female system, a number of females are mated to one or to a number of males. If it is the former, a number of females mated to one male, we have polygyny; if the latter, a number of females mated to a number of males, polygamy (or what, if there is little in the way of systematic contact among mating partners, me might call promiscuity). As far as uni-female systems are concerned, there are again two possibilities; one female may be mated to one male, what we know as monogamy, or one female may be mated to many males, what is termed polyandry." (Badcock, C. (1991) Evolution and Individual Behavior: An Introduction to Human Sociobiology Oxford: Blackwell. pp. 131)

"De Waal concluded that sexual behavior was primarily a mechanism to reduce tension and reconcile opponents after conflict and secondarily a mechanism to obtain food." (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 706)

"To recapitulate to this point, chimpanzees copulate in a ventro-dorsal position, and sexual behavior seems to have principally a reproductive function. Among bonobos, sexual behavior appears, in proximate terms, to serve principally a tension-reduction function and thereby to promote sociality, and although virtually any copulatory position can be used, females appear to prefer ventro-ventral mating and males appear to prefer ventro-dorsal mating." (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 706)

"Bonobos exhibit marked swelling for approximately 75% of the cycle, whereas chimpanzees show swelling for 50% or less of the cycle (Dahl 1986). Moreover, the intermenstrual interval for adult bonobos was measured to be 47 days, against 34-36 days for adult chimpanzees (Dahl 1986). In all of those regards also, they are more like the adolescent than the mature chimpanzee." (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 707)

"Not only do bonobos copulate throughout the female cycle, they have a briefer period of lactational amenorrhea, returning to sexual activity sooner after the birth of an infant than do chimpanzees (Thompson-Handler, Malenky, and Badrian 1984). They are thus similar to primiparous as opposed to multiparous chimpanzees. Bonobo females have also reported to be sexually receptive during lactation (Kano 1980; Nadler et al. 1981; Badrian and Badrian 1984) and even during pregnancy (Kano 1989). The data are clear that bonobo females are sexually receptive for comparatively longer periods of time than are chimpanzees. Paedomorphism in female anatomy and physiology appears to be the basis for the divergent sexual behavior, including female preference for a ventro-ventral copulatory position." (Blount, Ben G. (1990) Issues in bonobo (Pan paniscus) sexual behavior. American Anthropologist 92: 707)

"Homo erectus did occupy a broad habitat range, almost as broad as that occupied by the lion and the elephant. But it did not undergo a major population explosion, did not result in a wave of extinctions due to over-hunting (as happened later with Neolithic technology), and id not drive the other Australopithecenes extinct with much efficiency. Thus, we see a major increase in brain size without significant technological progress or any substantial increase in ecological dominance." (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 12)

"Thus, we have the paradox of Neanderthals using huge amounts of energy and food to power brains even larger than ours, but showing no signs of the ecological success or technological sophistication that we tend to expect form big-brained humans. This pattern of both Neanderthals and Cro-Magnons being highly encephalized, whether or not they showed the high technical skill and ecological dominance of modern humans, suggests that both sub-species encephalized for some reason unrelated to technical or ecological selection pressures." (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 14)

"Thus, the evolution of the human brain from 450 cc to 1300 cc occurred about as smoothly and gradually as evolution ever does; it was not a single 'punctuation' associated with a single speciation event (as in the punctuated equilibrium model of Eldredge & Gould, 1972), but was rather a long, uneven trend across at least four chronospecies (separately identifiable species directly related by descent), and spanning at least 1.6 million years, from about 1.8 mya to about 200,000 years ago. During this period, there was no identifiable periods of evolutionary 'stasis' during which brain size stabilized for a significant period of time (e.g. longer than 100,000 years or so); the evolutionary trend towards larger brain size appears to have had some 'momentum all its own, apart from climatic or ecological changes, which tend to result is sudden change followed by stasis (Eldredge & Gould, 1972; Vrb, 1989, 1992). These facts suggest that encephalization was driven by some evolutionary process occurring within our lineage, rather than by some selective force being imposed from the outside (e.g. from the physical habitat or biological econiche). (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished theses. pp. 17)

"Nevertheless, because relative brain size has been so often used as the index of brain evolution, its application must be reviewed here. Stahl's (1981) 'Encephalization Quotient' (EQ) measures how large a brain is in proportion to the size expected based on allometric regression with respect to body size. By this measure, the prosimians have average mammalian EQ's of around 1. The other great apes (gorillas, chimpanzees, orangutans) have EQ's around 2.5; the Australopithecenes had EQ's around 3.5. Homo habilis developed an EQ around 4.0, early Homo erectus started at around 4.5, and progressed to around 6.0, and archaic homo sapiens reached 7, the same as modern humans (Passingham, 1982). Thus, "from prosimians to apes to humans, there was a sevenfold increase in relative brain size" (Donald, 191). There is some controversy over how to calculate relative brain size. Estimates by Passingham & Ettlinger (1974) suggest that our brains are only about three times larger than the size expected for a primate to our build and size. Other estimates of our EQ range from 2.87 (Holloway & Post, 1982) to 6.93 (Jerison, 1973). In any case, the absolute tripling of brain size was accompanied by at least a relative tripling." (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 19)

"Shepard (1975, 1981, 1982) has suggested that the evolution of human language may have been facilitated by the evolution of hemispheric specialization, such that the capacities for grammatical and conceptual transformation underlying language in one hemisphere may represent modifications of more ancient capacities for the mental transformation of spatial representations that were originally carried out in both hemispheres. Similar ideas have been advanced by Bradshaw (1988, 1993) and Corballis (1983, 1991a,b). (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 22)

"Adults aside, the fetal brain required about 60% of total fetal energy before birth, imposing a heavy burden on maternal metabolism. The fetus' brain is so large that humans must be born relatively prematurely (about 7 months earlier than they should be, compared to other primate life-history and obstetric norms) through a substantially widened pervic structure. This 'obstetric dilemma' is so severe that human females suffer a far higher rate of death in childbirth than any other mammal. The reduction in sexual dimorphism form Homo habilis to Homo erectus was actually an increase in females size, this size increase may have been driven primarily by selection for a wider pelvic outlet to allow the birth of larger-brained babies." (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 25)

"Another kind of turnover-pulse hypothesis has been articulated by Calvin (1991), who emphasizes the possible role of glaciation cycles in facilitating human evolution. Until recently, Pleistocene glaciation was assumed to affect primarily upper latitudes, but recent paleoclimatology studies have suggested that glaciation had substantial effects on the temperature, rainfall, seasonality, and patchiness of resources in the equatorial zones of Africa (Foley, 1987). So there is a coincidence between the onset of glaciation cycles and the onset of encephalization in our lineage." (Miller, Geoffrey F. (1994) Evolution of the human brain through runaway sexual selection: the mind as a protean courtship device. unpublished thesis. pp. 28)


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