Title Sperm Wars
Author Robin Baker
Year Published 1996
Kind of Book Sexuality/Evolution
How strongly I recommend it 5/10
My Impressions If you've ever asked yourself why chimpanzee testicles are so much larger than gorilla testicles, this book is for you. We often think of sexual competition as being something that happens amongst male animals with their horns and claws, not something that happens amongst their sperm inside a female's uterus. This broadened the way I think about sexual selection. It is not just about which male has sex with the female, but about when he does and if his swimmers are powerful enough to beat out the ones already there (or that will be coming in the next few days.) Fair warning: This book was written in the 1990s and I'm not sure how well some of its claims hold up. I have heard some of the claims labeled controversial or incorrect in recent years. Some of Baker's theories seem pretty far -fetched or downright rubbish. This made it hard for me to fully believe anything that was said in the book and want to check them with other sources.
Date Read circa 2017
What question is the author trying to answer?
What is sperm warfare? How does it change the way we think about sexual selection and sexual competition?
Big Ideas
The first step to dealing with antisocial behavior is to understand it.
Males and Females often have conflicting goals in terms of reproductive success
Female Primates who hide when they are ovulating (humans) evolved this function because it gives them the evolutionary advantage of controlling when and with whom she conceives
Women's menstrual cycles are unpredictable from one month to the next
Because
Unpredictable menstrual cycles give the female control of when and with whom she conceives. Ie. It is more difficult for males to control who will father her offspring
Women experience sexual cravings both when they are ovulating and when they are not ovulating
Therefore
Women are not naturally conscious of when they are most fertile
Post-menopausal women still get horny
Because
Post-menopausal women are able "deceive" men that they are fertile still desiring sex after menopause. This prevents men from potentially abandoning them for younger and more fertile partners.
Men have a long refractory period when they have the opportunity to have sex again with the same woman
Men have a shorter refractory period when they have the opportunity to have a sex with a different woman
Because
There is little chance or increasing a woman's likihood to conceive by ejaculating into her twice in a row (as opposed to just one time). The sperm (and energy/resources used to make the sperm) would thus be wasted
SP**Animals do not expend energy/resources unless there is a utility
It is possible that by having sex again with a woman a man just ejaculated into, his penis may remove some of the sperm (thus decreasing her chances of conceiving)
Men unconsciously keep track of the last time they inseminated their partner and if there is likely a chance that she has been inseminated by another man in the meantime
Men desire sex with their partner more when she has been away from him (and may have had sex with other men)
Many couples have trouble conceiving
And
Women are likely to conceive with a man who is not her partner even though she has been trying, unsuccessfully, for some time to conceive with her primary partner
Because
Women are more likely to have sex with their partner during infertile phases of their cycle
Women are more likely to have sex with a man other than her partner during the fertile phases of their cycle
Women are less likely to insist men use contraception when they are ovulating
Men often never find out about women’s infidelities
Women's one-off infidelities are rarely discovered
Women's long term infidelities are only discovered 50% of the time
Men's testicles would be much smaller if they weren't sperm warfare
Men's penises would be much smaller if they weren't sperm warfare
Step-Dads sometimes behave worse towards their step-son or daughter after the woman has given them a child of their own
Porn is Arousing to men
Because
When a man watches another man having sex with a woman it makes him create more sperm in order to compete with the sperm likely to be in her already
Males perform cunnilingus in order to answer the question
1)is she healthy
2)is she fertile
3)has she recently had sex with another male
"They are seeking the answer to three questions. Is the female healthy? Is she fertile? And has she recently had sex with another male?" (the main one) pg76
Women care slightly less about their partners cheating then men do
Because
Men, unlike women, can be tricked into raising another man's child (which is a large investment)
Males are usually not as subtle about their infidelity as females
Because
There is more likely to be reprocutions for women caught sexually cheating then men
Different Men have different sized testes.
Therefore
Men have evolved different mating strategies based on their testicle size
Men with larger testes
-manufacture more sperm
-introduce more sperm per ejaculate
-tend to spend less time with each partner
-engage in sperm warfare more often
-engage in intercourse with women who will also be unfaithful.
Men with smaller testes
-manufacture less sperm
-introduce less sperm per ejaculate
-tend to more time with each partner
-tend to mate guard and be faithful
-avoid sperm warfare
Men ejaculate more when having sex than when masturbating/oral/heavy petting
Because
Men (unconsciously) ejaculate more when there is a greater chance their semen will inseminate a woman
Men ejaculate about 10% fewer sperm if they are wearing a condom
Precum is particularly fertile
When a man masturbates he will produce fewer sperm in his subsequent ejaculation
But
When a man masturbates the sperm in his subsequent ejaculation will be younger and more fertile
Ejaculating 2 days before intercourse provides the most fertile semen (highest chance of conception)
Men have wet dreams as a way to rid their testicles of old damaged/less fertile sperm
A high body temperature (during a flu or infection) can kill or damage a man's sperm
Women at the latitude of Britain and Canada are more likely to give birth in February and March
Meaning
Women at the latitude of Britain and Canada are more likely to conceive in June and July ie. Humans have a mating season in the early summer months
Stress hurts the chance of a female conceiving during sex
Children from poor families are twice as likely to die before reproducing as children from rich families
Miscarriages can be brought upon by stress
Miscarriages are more common when the to-be father dies, cheats, or leaves the woman
Women are less likely to use contraception with men who are not their partner
Women typically only leave relationships when they believe they can be with someone better than their current partner
Women are more likley to have a daughter when mating with a low-status man and a son when mating with a high-status man
Women's bodies bias the fertilization of girls when mating with a low-status man and boys when mating with a high-status man
It is easier for girls from a low socio-economic background to find high-value mates than girls
Because
Men tend to choose their mates more based on physical appearances
And
Women tend to choose their mates more based on socio-economic status
Any behavior we find sexually exciting is an adaptation that serves an evolutionary purpose (ie. Not a by-product)
Women may perform oral sex in order to (unconsciously) check for signs or smells of infidelity
Women like a men's butts
Because
The best indication of a man's health and hormones is the ratio between his waist and buttocks
The penis has evolved its size and shape to remove any sperm that is already present in the woman’s vagina upon penetration
Women only orgasm when their body judges that the orgasm is likley to enhance reproductive success
A woman's orgasm increases the amount of sperm that enter the cervix, thus increasing her chances of conceiving
80% of men who have sex with other men, also have sex with women
Homosexuality must be an adaptation
Because
Any gene that persists in a population at the 6% level can only be there if it imparts some reproductive advantage to the individual
Homosexuality is inherited via the mother's genes
Women are twice as likely to experience orgasm when stimulated by a woman than by a man
Biologists are reprimanded for suggesting that rape has been/can be a successful reproductive strategy for males to get their genes into the next generation
But
Historians are never reprimanded for suggesting that warfare benefited the nation who fought the war
To suggest that rape has been/can be a successful reproductive strategy for males to get their genes into the next generation is not the same as condoning it or being an rape apologist
Most rapists select women between 20-35 (ie. Women at their peak fertility) as their victims
Women are more likely to conceive from rape than from routine sex with a partner
Rapists who physically harm or kill their victims are more likely to choose women who are older (ie. Past peak fertility)
There is more rape during times of War
Because
1)During times of war Males who might otherwise defend their women are absent
2)During times of war the mobility and confusion of war make it very difficult for rapists to be tracked down and prosecuted
3)During times of war There is an ever-present risk of imminent death which makes males more likely to take chances they wouldn't otherwise take
Surprising Facts
"less than 1 per cent of the sperm in a human ejaculate are the elite, fertile ‘egg getters’, the remainder are infertile ‘kamikaze’ sperm whose function has nothing to do with fertilization but everything to do with preventing sperm from another man fertilizing the egg.” pg xii
"The average man and woman…will have penetrative sex about two thousand times in their lifetime….fewer than 7 children….This works out to about five hundred inseminations to produce each child." pg9
"Female baboons and chimpanzees develop large and conspicuous red, crusty swellings around the anus and vulva…male baboons and chimpanzees get turned on by these signals…" pg12
"a woman’s body allows sperm to remain fertile for no more than five days after being deposited inside her.."pg12
"…sperm seem to need about two days inside the female to reach peak fertility.”
Women's menstrual cycles are unpredictable from one month to the next
"The length of the menstrual cycle can be anything from fourteen to forty-two days." Pg13
“…the number of days from ovulation to the beginning of the next period is a fairly predictable fourteen days.”pg14
"[flowback occurs] about half an hour after ejaculation….Before this, a woman can stand up, walk around, even urinate, and she will not eject the flowback"
Each time she has sex, a woman’s body decides how many sperm to keep and how many to eject [in the flowback].”pg26
“4% of people are conceived via sperm warfare.”pg47 ie. After more than one man's sperm fought inside the uterus.
"Fraternal twins can have different fathers." pg47
“…10 per cent of children are in fact not sired by the man who thinks he is their father.” pg63
“The non-paternity level for children conceived will be even higher. This is because a woman is more likely to abort a child conceived via a man other than her long-term partner.” pg64
Children are much more likely to be abused or even killed by a stepfather than by their genetic father.
Sperm production correlates with the size of testes.
an average man produces around three hundred million sperm a day
An average man… ejaculates between 3 and 4 times a week. Pg92
“Men have a pair of tests of unequal size (on average, the right is 5 per cent larger).” p344
“80 percent of women have had sex with two different men within five days;
69 per cent within one day;
13 per cent within an hour; and
1 percent within thirty minutes.”pg181
It is a myth that some positions are more likely to get a woman pregnant than others
Only about 40 per cent of women have nocturnal orgasms
“In a study of American students published in 1982, it was found that girls who were exposed to an attempt at date rape were three times more likely to resume their relationship with the man concerned if his attempt succeeded that if it failed.”pg258
Men will have sex over their lifetime with about 12 women on average (1996)
Women will have sex over their lifetime with about 8 men on average (1996)
Men and Women produce 2 children on average (1996) pg. 282
Unknown Terms
Flowback: the female’s ejection of part of the inseminate that she has just received from the male…it
happens about half an hour after ejaculation….Before this, a woman can stand up, walk around, even urinate, and she will not eject the flowback. Each time she has sex, a woman’s body decides how many sperm to keep and how many to eject.”pg26
Blocker sperm: "sperm whose role is to prevent any later sperm from passing through to her cervical crypts and womb." (older sperm) pg51
Killer sperm: sperm who- roam around in search of sperm from other men to destroy. (younger sperm) pg52