Rather, there is no link between the timing of the flowback and the number of sperm retained.
Women on average eject roughly 35 percent of the sperm within thirty minutes of the time of insemination. If the woman has an orgasm, however, she retains 70 percent of the sperm and ejects only 30 percent. Lack of an orgasm leads to the ejection of more sperm. This evidence is consistent with the theory that women's orgasm functions to suck up the sperm from the vagina into the cervical canal and uterus, increasing the probability of conception. (p.76)
It turned out that women who are having affairs appear to time their copulations to coincide with the point in their ovulatory cycle when they are most likely to be ovulating and hence are most likely to conceive. (p.76)
To find how many sexual partners people in fact desire, the study of temporary and permanent mating asked unmarried American college students to identify how many sex partners they would ideally like to have [...] For the life time, men on average would like to have eighteen sex partners and women only four or five. (p.77)
In a typical study, a cow is placed in a bull pen, and after copulation the cow is replaced with an other cow. The bull's sexual response continues unabated with each new cow but diminishes quickly when the same cow is left in the pen. Males continue to become aroused to the point of ejaculation in response to novel females, and the response to the eighth, the tenth, or the twelfth female is nearly as strong as the response to the first. (p.80)
Twenty-nine percent of men and women questioned by the sex researchers Samuel Janus and Cynthia Janus state that sexual problems were the primary reason for their divorce, which makes that reason the most often mentioned. The potential costs inflicted by an unfaithful mate and by divorce potentially can be avoided by assessing sexual compatibility before making a commitment. (p.88)
As Robert Smith points out: A primary mate cannot always be available to defend his wife and children and, in his absence, it may be advantageous for a female to consort with another male for the protection he may offer.... absence of the primary mate [for example, when he is off hunting] may create the opportunity and need for extra bond mating.... a male may be inclined to protect the children of a married lover on the chance that his genes are represented among them. (p.89)
A lover may also serve as a potential replacement for the woman's regular mate if he should desert, become ill or injured, prove to be infertile, or die, which were not unusual events in ancestral environments. A permanent mate may fail to return from the hunt, for example, or be killed in a tribal war. Men' s status may change over time-the head man to whom a woman is married might be deposed, his position usurped, his resources co-opted. Women benefit by positioning themselves to replace a mate quickly, without having to start over again. A woman who must delay the replacement by starting over is forced to incur the costs of a new search for a mate while her own desirability declines. Women benefit from having men waiting in reserve. (p.89-90)
Evidence for the mate-switching function of casual sex comes from two sources. The first study found that women have affairs primarily when they are dissatisfied with their current relationship; in contrast, men who have affairs are no more unhappy with their marriage than men who refrain from affairs. A second study, by Heidi Greiling and me, revealed that women some times have affairs when they are trying to replace their current mate or in order to make it easier to break off with a current mate. (p.90)
One version of the better genes theory has been labeled the "sexy son hypothesis." According to this theory, women prefer to have casual sex with men who are attractive to other women be cause they will have sons who possess the same charming characteristics. Women in the next generation will therefore find these sons attractive, and the sons will enjoy greater mating success than the sons of women who mate with men who are not regarded as attractive by most women. (p.91)
( David M. Buss – The Evolution of Desire )
