Editing Concealed ovulation (section)

===Paternal investment hypothesis===

The [[paternal investment]] hypothesis is strongly supported by many evolutionary biologists.<ref name="Schroder 1993" /> Several hypotheses regarding human evolution integrate the idea that women increasingly required supplemental paternal investment in their offspring.  The shared reliance on this idea across several hypotheses concerning human evolution increases its significance in terms of this specific phenomenon.

This hypothesis suggests that women concealed ovulation to obtain men's aid in rearing offspring.  Schröder<ref name="Schroder 1993" /> summarizes this hypothesis outlined in Alexander and Noonan's 1979 paper:  if women no longer signaled the time of ovulation, men would be unable to detect the exact period in which they were fecund.   This led to a change in men's mating strategy:  rather than mating with multiple women in the hope that some of them, at least, were fecund during that period, men instead chose to mate with a particular woman repeatedly throughout her menstrual cycle.  A mating would be successful in resulting in conception when it occurred during ovulation, and thus, frequent matings, necessitated by the effects of concealed ovulation, would be most evolutionarily successful. A similar [[Bipedalism#Provisioning model|hypothesis]] was proposed by Lovejoy in 1981 that argued that concealed ovulation, reduced canines and [[bipedalism]] evolved from a reproductive strategy where males provisioned food resources to his paired female and dependent offspring.<ref>{{Cite journal|last=Lovejoy|first=C. Owen|date=1981-01-23|title=The Origin of Man|journal=Science|language=en|volume=211|issue=4480|pages=341–350|doi=10.1126/science.211.4480.341|issn=0036-8075|pmid=17748254|bibcode=1981Sci...211..341L}}</ref><ref>{{Cite journal|last=Lovejoy|first=C. Owen|date=2009-10-02|title=Reexamining Human Origins in Light of Ardipithecus ramidus|journal=Science|language=en|volume=326|issue=5949|pages=74–74e8|doi=10.1126/science.1175834|issn=0036-8075|url=http://doc.rero.ch/record/211449/files/PAL_E4439.pdf|pmid=19810200|bibcode=2009Sci...326...74L|s2cid=42790876}}</ref>

[[extended female sexuality|Continuous female sexual receptivity]] suggests human sexuality is not solely defined by reproduction; a large part of it revolves around conjugal love and communication between partners.  Copulations between partners while the woman is pregnant or in the infertile period of her menstrual cycle do not achieve conception, but do strengthen the bond between these partners.  Therefore, the increased frequency of copulations due to concealed ovulation are thought to have played a role in fostering [[pair bond]]s in humans.<ref name="Benagiano and Mori 2009">{{Cite journal
 | last1 = Benagiano | first1 = G.
 | last2 = Mori | first2 = M.
 | title = The origins of human sexuality: Procreation or recreation?
 | journal = Reproductive Biomedicine Online
 | volume = 18
 | pages = 50–59
 | year = 2009
 | issue = Suppl 1
 | pmid = 19281665
 | doi=10.1016/s1472-6483(10)60116-2
}}</ref>

The pair bond would be very advantageous to the [[reproductive fitness]] of both partners throughout the period of pregnancy, lactation, and rearing of offspring.  Pregnancy, lactation and caring for post-lactation offspring require vast amounts of energy and time on the part of the woman.  She must at first consume more food, then provide food to her offspring, while her ability to forage is reduced throughout.  Supplemental male investment in the mother and her offspring is advantageous to all parties.  While the man supplements the woman's limited gathered food, the woman is enabled to devote the necessary time and energy to the care of their offspring.  The offspring benefits from the supplemental investment, in the form of food and defense from the father, and receives the full attention and resources of the mother.  Through this shared parental investment, both man and woman would increase their offspring's chances for survival, thereby increasing their reproductive fitness.   In this way, natural selection would favor the establishment of pair bonds in humans.  To the extent that concealed ovulation strengthened pair bonding, selective pressure would favor concealed ovulation as well.

Another, more recent, hypothesis is that concealed ovulation is an adaptation in response to a promiscuous mating system, similar to that of our closest evolutionary relatives, [[bonobos]] and [[Common chimpanzee|chimpanzees]]. The theory is that concealed ovulation evolved in women to lessen paternity certainty, which would both lessen the chances of infanticide (as a father is less likely to kill offspring that might be his), and potentially increase the number of men motivated to assist her in caring for her offspring ([[partible paternity]]). This is supported by the fact that all other mammals with concealed ovulation, such as dolphins and [[gray langur]]s, are promiscuous, and that the only other ape species that have multi-male communities, as humans do, are promiscuous. It is argued that evidence such as the [[Coolidge effect]], showing that a man does not seem to be naturally geared towards sexual mate-guarding behavior (that is, preventing other males from having access to his sexual partner), supports the conclusion that sexual monogamy (though perhaps not [[Monogamy#Varieties in biology|social monogamy]] and/or pair bonding) was rare in early modern humans.<ref name="Ryan">{{cite book|author=Christopher Ryan Ph.D|author2=Cacilda Jethá Ph.D|name-list-style=amp|title=Sex at Dawn|isbn =978-0-06-220794-4 |publisher=HarperCollins|year=2012}}</ref>