Why Is Sex Fun?: The Evolution of Human Sexuality
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sex differences and, 47–49
Howler monkeys, concealed ovulation and, 82
Hrdy, Sarah, 71, 73–75
Human sexuality: apes compared to, 8–10
apparent inefficiency of, 67–68
continuous practice of sex and, see Sexual receptivity (female)
coparenting and, 29–30, 38
evolutionary biology and, 10–13
extramarital sex and, 5, 38–39, 68, 69–70
harems and, 4, 5–6, 37
internal fertilization and, 21–23
long-term sexual partnerships and, 4, 5–6
mammalian sexuality compared to, 1–10
monogamy and, 5–6, 82, 83
ovulatory signals and, see Concealed ovulation; polyandry and, 6
polygyny and, 6, 37
premarital sex and, 5
private sex and, 4
promiscuity and, 78, 79
proximity to sexual partnerships of others and, 4
sequential monogamy and, 6. See also Concealed ovulation; Females (human); Males (human); Menopause; Parental care (human); Recreational sex; Sexual receptivity (female)
Human signals, 128–30, 134–46
age, 135, 142
facial beauty, 137–38, 141
handicap principle of, 133, 144–45
male voice, 127–28
men’s muscles, 135, 136–37
natural selection and, 128–29
penis, 142–46
runaway selection model of, 131–32, 144
sex appeal and, 135, 141
sexual maturity, 128–29, 135, 142
sexual ornamentation, 138–41, 142–46
truth in advertising principle of, 133–35, 136–39
women’s breasts, 136, 138–39, 141
women’s fat, 135, 138–39, 141
Hunter-gatherers: conflict of interests and, 100
lactational amenorrhea and, 36
weaning and, 59
women and, 91, 93–94, 95, 100. See also Hunters, men as
Hunters, men as, 91–101
Aché Indians and, 93–98
extramarital sex and, 98–100
Hazda Indians and, 93, 95–96
meat provisioning and, 91–93
as providers, 98–99, 100
as show-offs, 98–100
women’s jobs versus, 91, 93–94, 95, 100
Hurtado, A. Magdalena, 93
Hutterite women, babies produced by, 103
Imprisonment of women, confidence in paternity and, 38
Infanticide: conflict of interests leading to, 100–101
many-fathers theory and, 73–75, 76
Infibulation, confidence in paternity and, 38
Insects, mating systems of, 7
Interior vagina, 45
Internal fertilization, 13
alternative opportunities foreclosed by child care and, 23–24
birds and, 22, 55–56
confidence of parenthood and, 25
evolutionary commitment of mammals to, 58–60
obligate parental investment and, 21–23
Inuit (Eskimo) men, hunting by, 95
Investment in young: external fertilization and, 61
male lactation and, 43
parental care and, 20–23, 35, 38, 56
Ismail the Bloodthirsty, Emperor of Morocco, 37
Jacanas (lily-trotters), sex-role-reversal polyandry and, 26–29, 57
Jackrabbits, lactation and, 59
Jones, Nicholas Blurton, 93
Jost, Alfred, 44
Kangaroos, parental care and, 17
Kaplan, H., 93
Ketengban tribe, phallocarps in, 142–43
Killer whales, menopause and, 125
Kingpin principle, aging and, 114–16
Kodric-Brown, Astrid, 133–34
Labia majora, 45
Labia minora, 45
Lactational amenorrhea, 36
Lactation (female), 23, 35–36
evolutionary commitment to, 58–60, 62
hormones and, 48–50
humans and, 23, 24, 35–36, 49–50
infanticide terminating, 73
mammals and, 23, 24, 49, 50
mammary gland development and, 48
nipple stimulation and, 50–51
origin of, 58
pregnancy and, 58
species differences and, 59
weaning and, 59. See also Lactation (male)
Lactation (male), 41–62
advantages of, 61–62
conditions favoring, 60–61
evolutionary commitment and, 58–60
hormones and, 48–50
male roles and, 53–54
nipple stimulation and, 50
physiological feasibility of, 43–52
pregnancy necessity and, 42, 49
psychological obstacles to, 62
spontaneous lactation and, 42, 51–52, 60
starvation recovery and, 51
technological possibility of, 61–62
Langur monkeys, concealed ovulation and, 79
Lek mating system, of hammer-headed fruit bats, 7, 8
Life span, female reproduction and, 105
Lily-trotters. See Jacanas
Lions: infanticide and, 73
parental care and, 2–3, 53–54
Long-Tailed Widowbirds, tails as signal and, 130, 132
Macaques, ovulatory signals and, 82. See also Barbary macaques; Rhesus macaques; Stumptailed macaques
Male lactation. See Lactation (male)
Male pseudohermaphrodites, 46–47
Males (human): American men, 101–2
divorce and, 102
duration of fertility of, 103, 115
facial beauty and, 137–38
mammary gland development and, 48–50, see also Lactation (male)
menopause and, 5
muscles and, 135, 136–37
in New Guinea, 90–91, 95
parental care and, 4, 6, 15, 16, 19, 21, 22, 24, 25, 29–30, 35–38, 71–73, 75, 102
penis of, 142–46
as providers, 98–99, 100, 102
role of, 89–102
sexual maturity of, 128–29, 135, 142
sexual ornamentation and, 140, 142–46
as show-offs, 98–100, 102
voice change and, 127–28. See also Extramarital sex; Hunters, men as; Lactation (male)
Males (mammalian): duration of fertility of, 103, 105–6, 115
infanticide and, 73–74
mammary gland development and, 48, see also Lactation (male)
meat provisioning and, 92
menopause and, 106–7
parental care and, 2–3, 7, 15, 21, 24, 25–34, 55–58
post copulatory desertion and, 23–25
role of, 2, 7, 15
sex-role-reversal polyandry and, 26–29
signals and, 130, 131–34, 140. See also Lactation (male)
Mammalian sexuality, 2–4
fertility time span and, 4
for fertilization, 3, 64–65, 66–67
harems and, 5, 78, 79, 80, 82, 83
human sexuality compared to, 1–10
male’s role and, 2, 7
mating systems, 7–8
menopause and, 4
one-night stands and, 5
ovulatory signals and, 3, 64
public sex and, 3. See also Females (mammalian); Internal fertilization; Males (mammalian); Parental care (mammalian)
Mammary gland development, hormones and, 47–50. See also Breasts; under Lactation
Mann, Thomas, 88
Mantises, sexual cannibalism and, 7, 11–12
Many fathers theory, of concealed ovulation, 71, 73–75, 76, 79, 84
Marmosets: as monogamous, 78
ovulatory signals and, 78
parental care and, 54
Marriage, by humans, 4
Marsupial mice, 8
menopause in males of, 106–7
sex for fertilizatio
n and, 66
Marsupials: internal fertilization and, 13
lactation and, 50, 58. See also Kangaroos
Mating systems: concealed ovulation and, 79–80
evolutionary changes and, 80–88
of primates, 78–79, 80–88
Men. See under Male
Menopause, 5, 10, 103–25
aging and, 109–13
burden of parental dependence of child and, 116–17
costs and benefits of, 116–20
definition of, 4
depletion and aging of egg supply and, 107–9, 115
extended role of postmenopausal women and, 118–20
importance to society of memories of old women and, 120–24
increase in expected life span and, 104–5
kingpin principle and, 114–16
in mammals, 106–7
more children produced by, 116–25
risk of death in childbirth and, 117–18
risks in infants of older mothers and, 118
Menstrual cycle, lactational amenorrhea and, 36. See also Menopause
Mice: aging and, 113
duration of fertility of, 106, 115
mammary glands in male, 48
repair versus reproduction and, 112–13. See also Marsupial mice
Midwife toads, parental care and, 16, 26
Missing Link, in concealed ovulation evolution, 80–88
Mixed reproductive strategy, of Pied Flycatchers, 33, 34
Møller, Anders, 77–88
Monkeys: concealed ovulation and, 82
monogamy and, 82
promiscuous mating system of, 82, 83. See also Night monkeys; Spider monkeys
Monogamy: concealed ovulation and, 79–81, 84–86
daddy-at-home theory and, 71–73, 75
of humans, 5–6, 82, 83
of primates, 78, 79, 82, 83
Monotremes: internal fertilization and, 22
lactation and, 58
Mormons, polygyny and, 37
Mullerian ducts, 45
Mullerian inhibiting hormone, 45
male pseudohermaphrodites and, 47
Muscles, as signal in human males, 135, 136–37
Napoleon the Third, 67
Natural selection, 104
behavior and, 16
concealed ovulation and, 87
lactation and, 60
male lactation and, 61
menopause and, 104
parental care and, 16–18
repair and reproduction and, 109–13
sexuality and, 10–13
signals and, 128–29
vertebrate limbs and, 87
New Guinea: bride prices in, 141
men’s role in, 90–91, 95
phallocarps in, 142–43
Night monkeys, concealed ovulation and, 79
Nizam of Hyderabad, 37
Noonan, Katharine, 71–73, 75
Nursing. See under Lactation
O’Connell, James, 93
Octopus, big-bang reproduction (semelparity) and, 7
Offspring, conflict of interest between parents and, 100–101
Olfactory signals, 3, 129
One-night stands, 5
On the Origin of Species (Darwin), 10
Opportunity. See Foreclosed opportunity
Orangutans: concealed ovulation and, 82
head shape indicating sex and, 130
humans compared to, 9
one-night stands and, 5
ovulatory signs and, 78
penis of, 143, 144
sexuality of, 9
Oring, Lewis, 27
Ostriches, parental care and, 17
Ovaries, 44
Ovulatory signals, 3, 130
evolutionary changes in, 80–88
in mammalian sexuality, 64, 77–78
in primates, 64, 77–78, 82, 130. See also Concealed ovulation
Parental care, 15–39
alternative opportunities foreclosed by child care and, 20, 23–24, 35–37, 38
battle of the sexes and, 18–20
confidence of parenthood and, 20, 24–25, 37–38, 38
male lactation and, 53–54
sex differences in obligate parental investment and, 20–23, 35, 38
Parental care (human), 2, 4, 6, 15, 34–38
alternative opportunities foreclosed by child care and, 23–24, 35–37
battle of the sexes and, 18–20
burden of long period of, 116–17
confidence of parenthood and, 24–25, 37–38
conflict of interests and, 100–101
coparenting and, 29–30, 38
females and, 4, 21–24, 25, 29–30, 35–38, 102
males and, 4, 6, 15, 16, 19, 21, 22, 24, 25, 29–30, 35–38, 71–73, 75, 102
polygyny and, 37
recreational sex and, 68–70
sex differences in obligate parental investment and, 21–23, 35
unwed mothers and, 6
Parental care (mammalian), 2–3, 7, 13, 15–34
alternative opportunities foreclosed by child care and, 23–24, 56
battle of the sexes and, 18–20
choices in, 16–18
confidence of parenthood and, 24–25, 56
coparenting, 29–34, 56
females and, 7, 15–16, 21–34, 55–57
lactation and, 53–54
male post-copulatory desertion and, 23–25
males and, 2–3, 7, 15, 21, 24, 25–34, 55–58
natural selection and, 16–18
sex and, 69
sex differences in obligate parental investment and, 22, 56
sex-role-reversal polyandry and, 26–29
Parenthood, confidence of. See Confidence of parenthood
Parricide, conflict of interests leading to, 100–101
Paternal care, 2–3. See also under Male
Peacocks, 8
tail of, 132
Penis, 44
internal fertilization and, 21
as signal in human males, 142–46
Penis shaft, 45
Phalaropes. See Wilson’s Phalaropes
Phallocarps, 143–44
Pheromones, 77
Pied Flycatchers: coparenthood and, 30–34
sex for fertilization and, 66–67
Pigeons: lactation and, 42, 56
small eggs of, 27
Pilot whales, menopause and, 107, 124–25
Placentals, lactation and, 48, 58
Platypus, internal fertilization and, 22
Plummage, as signal, 130
Polyandry, 36
humans and, 6
sex-role-reversal, 26–29, 36, 57
Tre-ba of Tibet and, 36, 37
Polygamy, harems and, 6
Polygyny: coparenthood in Pied Flycatchers and, 30–34
humans and, 6, 37
Porcupines, aging and, 113
Post-copulatory desertion by males, 23–25
exceptions to, 25–34
Pregnancy: duration of, 58
lactation and, 42, 49, 58
Premarital sex, humans and, 5
Primary female, polygyny in Pied Flycatchers and, 30–31, 32
Primates: concealed ovulation studied with, 77–88
family tree of, 80–88
mammary glands and, 48
mating systems of, 78–79, 80–88
ovulatory signals and, 64, 77–78, 82, 130
promiscuity of, 78–79, 80, 82, 83. See also specific primates, i.e. Apes; Baboons; Chimpanzees, etc.
Primordial gonad, 44, 45
Private sex, humans and, 4
Progesterone, lactation and, 49–50
Prolactin, lactation and, 48, 49
Promiscuity: concealed ovulation and, 84, 85
of humans, 79
of primates, 78–79, 80, 82, 83
Prostate gland, 44
Prostitution theory, of concealed ovulation, 70
Providers, men as, 98–99, 100, 1
02
Proximate mechanism, ultimate explanations versus, 108–9
Pseudohermaphrodites, 46–47
Pubic hair, sexual maturity in humans indicated by, 135, 142
Public sex, mammals and, 3
Pygmy chimpanzees. See Bonobos
Pythons, parental care and, 23
Rabbits, duration of fertility of, 115
Rats (male), mammary glands and, 48
Recreational sex, 4, 5, 10, 66, 67
coparenting and, 68–70
extramarital sex and, 69–70
sex-to-promote-family-values theory and, 68–69. See also Concealed ovulation; Sexual receptivity (female)
Rennell Island, consumption of fruits and seeds by birds and, 122–23
Repair and maintenance, 109–13
death and accidents and, 113
reproduction versus, 112–13
Repair and reproduction, natural selection and, 109–13
Reproductive strategy, 17
Reptiles: therapsid, 58
vivipary and, 22
Rhesus macaques, duration of fertility of, 106, 115
Rockefeller, Nelson, 67
Runaway selection model. See Fisher’s runaway selection model of signals
Saddleback tamarin monkeys, paternal care and, 3
Salmon, big-bang reproduction (semelparity) and, 7, 107
San (Bushmen): fat in women of, 138
men as hunters and, 95
Sandpipers. See Spotted Sandpipers
Scrotum, 45
Sea birds, pair bonds and, 8
Seahorses: male pregnancy and, 42
parental care and, 16
Seals. See Arctic seals
Secondary female, polygyny in Pied Flycatchers and, 31–32
Semelparity. See Big-bang reproduction
Seminal vesicles, 45
Senescence. See Aging
Sequential monogamy, humans and, 6
Sex appeal, 135
extramarital sex and, 141
as signal, 135, 141
Sex chromosomes, 43–44, 45, 47
Sex differences, hormones and, 47–49
Sex for fertilization. See Fertilization, mammals having sex for
Sex for fun. See Recreational sex
Sex in private, humans and, 4
Sex in public, mammals and, 3
Sex-role-reversal polyandry, 26–29, 36, 57
Sex-to-promote-family-values theory, of recreational sex, 68–69
Sexual cannibalism, 7, 11–12
Sexual evolution, 11–13
Sexual maturity, signals indicating, 128–29, 130, 135, 142
Sexual ornamentation: function of, 145
in men, 140, 142–46
in women, 138–41
Sexual receptivity (female), 5, 64–65, 67
better-genes-through-cuckoldry theory of, 70
coparenting and, 68–70
daddy-at-home theory and, 71–73, 75
extramarital sex and, 69–70
infanticide and, 73–75, 76
many-fathers theory and, 71, 73–75
Sexual signals. See Signals
Shore birds, sex-role-reversal polyandry and, 26–29, 57