Diamond, Jared M.;
Why Is Sex Fun?: The Evolution of Human Sexuality
Basic Books, 1998 (c1997), 176 pages
ISBN 0465031269, 9780465031269
topics: | sex | biology
Preface:
Among the unusual aspects of human sexuality that I discuss
are female menopause, the role of men in human societies,
having sex in private, often having sex for fun rather than
for procreation, and the expansion of women's breasts even
before use in lactation.
[opening lines:]
If your dog had your brain and could communicate, and if you asked it what
it thought of your sex life, you might be surprised by its response. It
would be something like this:
Those disgusting humans have sex any day of the month! Barbara
proposes sex even when she knows perfectly well that she isn't
fertile—like just after her period. John is eager for sex all
the time, without caring whether his efforts could result in a
baby or not. But if you want to hear something really
gross—Barbara and John kept on having sex while she was
pregnant! That's as bad as all the times when John's parents
come for a visit, and I can hear them too having sex, although
John's mother went through this thing they call menopause
years ago. Now she can't have babies anymore, but she still
wants sex, and John's father obliges her. What a waste of
effort! Here's the weirdest thing of all: Barbara and John,
and John's parents, close the bedroom door and have sex in
private, instead of doing it in front of their friends like
any self-respecting dog!
These are unusual because:
a) in most of the 4300 mammal species, male and female meet only to copulate,
the male rarely contributes to child-raising. Exceptions include
polygynous male zebras and gorillas with harems of females, male gibbons
paired off with females as solitary couples, and saddleback tamarin
monkeys, of which two adult males are kept as a harem by one polyandrous
adult female.
b) in most mammal species, female ovulation is widely advertised, (e.g. area
around the vagina turning bright red, special smells, etc.).
c) Except for a handful of species like bonobo chimps and dolphins, sex is
only when the female is oestrous. sex is also expensive - it can cost
your life to lower the guard, so having it for fun is quite unusual.
d) in most cases, sex is public. among chimps, a couple may pair off for a
couple of days, but the female may also have public sex with some other
male within the same estrus cycle.
d) menopause is not known in the animal kingdom.
[I wonder if menopause known in ancient times, when life expectancy
was 40? It must have been, for many indiv's would have lived to be
80-100. Hence it is not an artifact of the unprecedented rise in
human longevity in the last few hundred years. At the same time, it
can't be ruled out that other species experience it but few specimens
live long enough for us to know. - AM]
The male of several species of spiders and mantises is routinely eaten by his mate just after or even as he is copulating with her. This cannibalism clearly involves the male's consent, because the male of these species approaches the female, makes no attempt to escape, and may even bend his head and thorax toward the female's mouth so that she may munch her way through most of his body while his abdomen remains to complete the job of injecting sperm into her. . . . [Reason: Genes survive, not the organism.] For some species of spiders and mantises living at low population densities, a male is lucky to encounter a female at all, and such luck is unlikely to strike twice. The male's best strategy is to produce as many offspring bearing his genes as possible out of this lucky find. The larger a female's nutritional reserves, the more calories and protein she has available to transform into eggs. If the male departed after mating, he would probably not find another female and his continued survival would thus be useless. Instead, by encouraging the female to eat him, he enables her to produce more eggs bearing his genes. In addition, a female spider whose mouth is distracted by munching a male's body allows copulation with the male genitalia to proceed for a longer time. [p.16-17] Most fathers make some contribution to their children, even if it's just food or defense or land rights. We take such contribution so much for granted that they're written into law: divorced fathers owe child support; an unwed mother can sue a man for child support if geetic tests prove that he is her child's father. [21] Most male mammals have no involvement with either their offspring or their offspring's mother after inseminating her; they are too busy seeking other females to inseminate. [21] [If] the newly fertilized, laid, or hatched egg has absolutely zero chance of surviving unless it is cared for by one parent [then] there is indeed a conflict of interest. Should one parent succeed in foisting the obligation of parental care onto the other parent and then going off in search of a new sex partner, then the foister will have advanced her or his genetic interests at the expense of the abandoned parent. [26]
Whether it actually pays you to desert depends on whether you can count on your old mate to finish rearing the kids, and whether you are then likely to find a receptive new mate. [It is as if they are playing a game of chicken.] Which parent is more likely to back down? The answer depends on three considerations: 1. which parent has more invested in the fertilized egg; [2. whether the chances of propagating the genes by finding alternate partners is greater than that of looking after the current offspring;] and 3. the parent's confidence in paternity or maternity of the egg. [27] By the end of a nine-month pregnancy a human mother's expenditure of time and energy is colossal in comparison with her husband's or boyfriend's pathetically slight investment during the few minutes it took him to copulate and extrude his one milliliter of sperm. [Leads to the lactation / guarding of eggs by females. In organisms where the inputs are equal, e.g. in external fertilization, the father, if he is sure of having inseminated the eggs - as in (some frogs or fish), may also look after the eggs' safety, thus ensuring at least the survival of those genes. ] [31] A man produces about two hundred million sperm in one ejaculate -- or at least a few tens of millions, even if reports of a decline in human sperm count in recent decades are correct. By ejaculating once every 28 days during his recent partner's 280-day pregnancy - a frequency of ejaculation well within the reach of most men -- he would broadcast enough sperm to fertilize every one of the world's approximately two billion reproductively mature women. That is the evolutionary logic that induces so many men to desert a woman immediately after impregnating her and to move on to the next woman. A man who devotes himself to child care potentially forecloses many alternative opportunities. [p.33, Argument 2 from p.27 above] [Female mammals are confident of paternity, but] Male parental care would be a bad evolutionary gamble. [34]
One type is those species whose eggs are fertilized externally. The female ejects her not yet fertilized eggs; the male, hovering nearby or already grasping the female, spreads his sperm on the eggs; he immediately scoops up the eggs, before any other males have a chance to cloud the picture with their sperm; and proceeds to care for the eggs, completely confident in his paternity. [35] [Second type - Sex-role-reversal-polyandry] Big females compete fiercely to acquire a harem of smaller males, for each of which in turn the female lays a clutch of eggs, and each of which proceeds to do most or all the work of incubating the eggs and rearing the young. The best known of these female sultans are the shore birds called jacanas (alias lily-trotters), Spotted Sandpipers, Wilson's Phalaropes. [Reason for reversal - the chicks are precocial, implying much development in the egg stage; hence a single parent can more easily raise them; also this is why the females are larger - four eggs constitute upto 80% of a female sandpiper's weight. But then since these are shore birds, there is a high percentage of predation - so the male is better off if the eggs for some reason are lost, to have the female rested to do a second round (which she may of course do with another male also). p.38 ]
Third type, like humans, is where the child bearing is so onerous that a single parent would not be able to do it. Most birds. But here too, most males philander (MRS), and many females are content to be the second-woman (often, e.g. the Pied Flycatchers, they are tricked) p.42] Don Giovanni - seduced 1,003 women in Spain alone - one Spanish woman every eleven days. In contrast if a male Pied Flycatcher temporarily leaveshis mate (for instance, to find food), then on the average another male enters his territory in ten minutes and copulates with his mate in thirty-four minutes. Twenty-nine percent of all observed copulations prove to be EPC's, and an estimated 24 percent of all nestlings are 'illegitimate'. [45]
Women with two husbands have as many offsprings as those with one; polyandry arose to prevent land-division; brothers marry same wife; in contrast, female phalarope - with one male - 1.3 chicks, two - 2.2, and 3.7 with three (hmmm - third case - data sanity?). See Nayar's TC p. 75qq] Polygyny paid off well for nineteenth century Mormon men, whose average lifetime output of children increased from a mere seven children for Mormon men with one wife to sixteen or twenty children with two or three wives, respectively, and to twenty-five for church leaders, who averaged five wives. [49] In chromosomes 1 through 22 the two chromosome pairs are identical. Only chromosome 23 is unpaired and that too only for males - who have a big chromosome (X) paired with a small one (Y). Women have two paired X chromosomes. Among non-reproductive functions, colour vision is determined by the X chromosome. If a Y chromosome is present, the bet-hedging gonad begins to commit itself in the seventh week to becoming a testis, but if there is no Y chromosome, the gonad waits until the thirteenth week to develop a ovary . . . People with one Y and two X chromoomes turn out most like males, whereas people with three or just one X chromosome turn out most like females. [54] 'Being a male is a prolonged, uneasy, and risky venture; it is a kind of struggle against inherent trends toward femaleness.' - endocrinologist Alfred Jost. [55] embryos also start out hedging with two sets of ducts, known as the Mullerian ducts and Wolffian ducts. In the absence of testes, the Wolffian ducts atrophy, while the Mullerian ducts grow into a female fetus's uterus, fallopain tubes, and interior vagina. With testes present, the opposite happens: androgens stimulate the Wolffian ducts to grow into a male feturs's seminal fesicles, vas deferens, and epididymis, and the testicles produce a protein called Mullerian inhibiting hormone. [58] [enzyme defects - some male hermaphrodites are more according to the norms of "female pulchritude" - bigger breasts, long legs,] cases have turned up repeatedly of beautiful women fashion models not realizing that they are actually men with a single mutant gene [that prevents an enzyme creation/function [you found out when you fail to menstruate - p.60] [Lactation - male and female - p. 62-70 - surrogate mothers can produce some milk within three or four weeks: earlier, put the infant or a puppy to the breast repeatedly (e.g. mother wanting to replace sickly daughter). Modern times - breast pump every few hours in preparation. ] Breast development occurs commonly and spontaneous lactation occasionally, in men recovering from starvation. Thousands of cases were recorded in priwoners of war released from concentration camps after WWII - five hundred in survivors of one Japanese POW camp alone. Starvation inhibits not only the hormones, but also the liver, which destroys the hormones. When normal nutrition is resumed, the glands producing hormones recover much faster than the liver. [66-7] [Dyak fruit bats - may have males and females nursing the baby 67-8] PREDICTION: Human male lactation: Paternity buttressed by DNA testing will make expectant fathers to make milk via breast stimulation and hormonal injections. [Will promote] a type of emotional bonding of father to child now available only to women. Many men, in fact, are jealous of the special bond arising from breast-feeding, whose traditional restriction to mothers makes men feel excluded. . . . Many of us choose to renounce murder, rape, and genocide, despite their advantages as a means for transmitting our genes, and despite their widespread occurrence among other animal species and earlier human societies. Will male lactation become another such counter-evolutionary choice? [80-81]
fins of ancestral fishes --> legs in reptiles, birds, mammals; front
legs --> bird wings,
bird wings --> penguin flippers,
mammal legs --> whale flippers
Similarly, concealed ovulation, boldly advertised ovulation, monogamy,
harems, promiscuity, etc have repeatedly been transmuted into each
other, reinvented and lost. [114]
[Studies on Paraguay's Northern Ache Indians by Kristen Hawkes of U. Utah: Hunters bring in 9.6Kcals on avg for the 10K by the woman. While the peak for hunters is much higher - 40K for the occasional peccary, the median, at 4.7K is much less, and] the Ache' men would do better in the long run by sticking to the unheroic 'woman's job' of pounding palms than by their devotion to the excitement of the chase. [Real reasons may be social standing] Ache' women, asked to name the potential fathers of 66 children, named an average of 2.1 men per child [their sex partners at the time of conception). Good hunters were named more often than poor hunters. Reproductive strategies for males - 'provider' vs 'showoff' - showoff is better - why? Women prefer the provider for husband, but may trade EPC with the showoff for the occasional extra meat. [130] Time budget studies show that American working women spend on the average twice as many hours on their responsibilities. When husbands are asked, they tend to overestimate their own hours and to understimate their wives hours. That is why the question What are men good for? continues to be debated within our societies. [135]
appeal to the opposite sex may depend on specific parts of the body, as is well known for humans. In an experimenting demonstrating this point, the tails of male Long-Tailed Widowbirds, an African species in which the male's sixteen inch tail was suspected of playing a role in attracting females, were lengthened or shortened. It turns out that a male whose tail is experimentally cut down to six inches attracts few mates, while a male with a tail extended to twenty-six inches by attaching an extra piece with glue attracts extra mates. [171] The Great Tit has a white stripe on the breast which serves as a signal of social status. Experiments with radio-controlled tit models placed at bird feeders show that live tits flying into the feeder retreat if and only if the model's stripe is wider than the intruder's. . . . Why should a perfectly good Great Tit retreat from food just because it sees another bird with a slightly wider black stripe? [Unlikely to imply intimidating strength; can lead to genetic movement towards increadingly thicker stripes.] These questions are still unresolved. [172]
Signals such as throwing away money (indicative of wealth), or a peacock's extra long tail are evolutionarily useful, and are not only honest signals, that inferior animals could not afford [Amos Zahavi] but also favouring survival, or being closely linked to traits favouring survival [Brown and Brown]. e.g. large antlers in deer - need bio-energy resources - but also help in fighting off other males. ] 175 Human signals include faces, smells, hair color, men's beards, and women's breasts. What makes those structures less ludicrous than a long tail as grounds for selecting a spouse? If we think that we have a signaling system immune to cheating why do so many people resort to makeup, hair dyes, and breast augmentation? [177] . . . we humans still carry the legacy of hundreds of millions of years of vertebrate evolution engraved deeply into our sexuality. Over that legacy, our art, language, and culture have only recently added a veneer. [191] [Three honest measures of individual capability in humans: muscles (more useful than antlers), facial beauty (face is expressive; age, malnutrition, and injury shows quickest on face), woman's body fat (needed for lactation, indicative of surplus resources). 180-1] [Location of excess fat in breasts and hips - can't be on limbs, therefore torso. Where on torso can vary - more on buttocks for some groups - e.g. women of the andaman island tribes - but excess fat on the lactation region is significant - it acts as a deceptive signal of lactation capability. 183]
At first we seem devoid of exaggerated signaling structures comparable to a widowbird's sixteen-inch tail. On reflection, however, I wonder whether we actually do sport such a structure: a man's penis. [ 187: Evidence - differences with apes; what men "want" (phallocarps 2 ft long; ), ] In response to my question as to why they wore phallocarps, the Ketebangans replied that they felt naked and immodest without them. . . . they were otherwise completely naked and left even their testes exposed. . . . Starting from a 1.5 inch ancestral ape penis similar to the penis of a modern gorilla or orangutan, the human penis increased in length by a runaway process, conveying an advantage to its owner as an increasingly conspicuous signal of virility. [Who is it intended for - may be for male dominance as much as for attracting females (which is doubtful) -190]
1. The animal with the weirdest sex life 2. Battle of the sexes 3. Why don't men breast-feed their babies? The non-evolution of male lactation 4. Wrong time for love: the evolution of recreational sex 5. What are men good for? The evolution of men's roles 6. Making more by making less: the evolution of female menopause 7. Truth in advertising: the evolution of body signals. --- blurb: Why are humans one of the few species to have sex in private? Why do humans have sex any day of the month or year—including when the female is pregnant, beyond her reproductive years, or between her fertile cycles? Why are human females the only mammals to go through menopause? Why is the human penis so unnecessarily large? Why do we differ so radically in these and other important aspects of our sexuality from our closest animal relatives and ancestors?With wit and fascinating scientific expertise, the author of The Third Chimpanzee explores the mystifying evolutionary forces that gave shape to our sexual distinctions and shows how they contributed to what it means to be uniquely human.