Talk:Concealed ovulation

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Article listed on Wikipedia:Votes for deletion July 2 to July 9 2004, discussion may be found at Talk:Concealed ovulation/Delete.

red lips

why is the concept of red lips seen as "concealed". i learned different then you describe here. the BODY is defenityly reaction depite what modern genderx people insist to. — Preceding unsigned comment added by 85.149.83.125 (talk) 10:10, 28 July 2022 (UTC)

Removed paragraph

Pulled this paragraph out because I don't think it is supported by the concensus of scientific literature. If you can source this as an accepted, published theory, please be bold and add it back. I've done a significant edit to this article based on my memory of a Scientific American article. This article would be much stronger with sourcing of the theories . Rossami 22:01, 2 Jul 2004 (UTC)

But if the female does manage to sneak off and copulate with another male, she can get meat from that other male for herself and her offspring -- giving her an incentive to "cheat". So the same pair bonding that cements a male to "his" female also leads, inevitably, to jealousy, fratricide between males, and even male violence toward his mate, to "keep her in line".

And I cut these paragraphs because they didn't seem to flow well but I couldn't figure out where to put them that would be any better. They're a bit of a tangent. Rossami 22:01, 2 Jul 2004 (UTC)

Female humans may not be able to consciously articulate why some males seem more masculine than others, but unconscious parts of their minds, adapted by evolution, can spot those signs.

And once again, concealed fertility aids the female -- since the male can never be sure when the female conceives, he can never be sure that a particular child is his; he must take his chances and support all "his" mate's offspring on the hope they are his.

An Objection

I have to object to the entire idea that evolution is intelligent, which is implied by the title verb of "concealed."

• Scientific investigation indicates that fertile women produce pheromes which are perceptible.
• "Rhythm" awareness of fertility has been discovered in human societies as far back as we look. This is further clarified by the usual practice of menstrual taboo practices, the taboo tent for menstruating women, etc.
• Year-round sexual activity can be explained quite a bit more easily by the fact that humans have no single environment; they cannot be sure of famine or bounty conditions and therefore need to be able to mate at any time.
• Human infants are helpless for longer than any other young. They require complete attention for two to five years. Therefore, it is very important for there to be young, and it requires frequent mating to ensure reproduction. As complex organisms, humans are tenuous in utero, and human females produce a single child at a time.
• Infant mortality in the evolutionary period would have been staggeringly high. After adding miscarriage into loss by predation, famine, and disease, you have all sorts of benefits to tricking not the male, but the female, into being pregnant year round.

Additionally, the "facts" are off.

• Bonobo chimps have recreational sex. In fact, their sex (infamous for being same-sex as often as different sex) functions as a social bonding ritual, as an apology, a reassurance, and an erotic act.
• Making blanket statements that "women prefer" is a generalization so broad as to stagger the imagination.
• Children look like their fathers to prevent infanticide? If alpha males are parenting but chump betas are rearing, wouldn't it be the dumbo beta who looks into the infant's eyes, sees the local bully, and then gets duped? How?

To me, this entire approach is mistaken, from its title to its conclusions. Geogre 20:17, 9 Jul 2004 (UTC)

Good evening, Geogre. I don't know that anyone would say that evolution is "intelligent" except as a bit of poetic license. I certainly did not read any such implication into the title. If you have a suggestion for a better title though, please move the article there. Some of your other concerns are quite valid. Even though this is a published theory, it is still a disputed theory. The article still has a ways to go to be fully fact-based and NPOV. Perhaps we should open an "objections" section at the bottom of the article? Having said that, a few of your objections have been addressed (to some degree) in the published literature. I'll try a recap below so we can build on each of them independently. Thanks for your help. Rossami 22:45, 9 Jul 2004 (UTC)

Ok, first let me apologize for the pugilistic tone. I do realize that folks are working in good faith, and my final comment, in particular, was ill-tempered. My problem with the title is the "conceal" requires an agent and implies intent. Perhaps I'm overly sensitive to language, but I cannot read the word without an implication of intention.

As for what to do with objections, let me make it clear that I recognize the validity and repute of the research presented here, but it is still a minority view that is highlighted against the older views which I more or less present. If you'd like, I can write an "other views" section at the end that opens something like, "The idea that concealed ovulation is an adaptation whose primary benefit is in allowing the alpha male genes to pass on in a context of beta male nurturing is one explanation of many. The same evolutionary adaptation can be viewed as arising because..." and then go to some of the objectionary grounds I've outlined. As for the matters of fact that you outline below, I will interline my responses and apologize for the formatting mess that creates. Geogre 01:23, 10 Jul 2004 (UTC)

---

• Scientific investigation indicates that fertile women produce pheromes which are perceptible.
  • Agreed, but the pheromones rarely (never?) reaches the level of conscious perception. If fertility is incompletely concealed, does it discredit the entire theory? Rossami
    • This is a hard question. The idea is that they make women more attractive to men, or more lustful. It does not need to rise to the level of consciousness. That alone would not refute the idea that fertility increases competition for the female and allows the dominant males to prevail, but I would suggest that a beta male would know that the "hot chicks" were being nabbed by the dominant male and would note the infidelity of the women who were then, only 8 days later, claiming to be theirs. Geogre 01:23, 10 Jul 2004 (UTC)
• "Rhythm" awareness of fertility has been discovered in human societies as far back as we look. This is further clarified by the usual practice of menstrual taboo practices, the taboo tent for menstruating women, etc.
  • While the female may be aware of her place in the cycle, the male may not have access to the same information. (I'm not sure I see the correlation with the menstrual taboos. Can you elaborate?) Rossami
    • I think this is a much more serious impediment to this article's theory. First, the theory of this article has been used to argue that taboos have been the result of male uncertainty about parenting and that making menstruating women ritually unclean makes all males mate only when women are fertile (the period of taboo is often much longer than the period itself). However, what I'm saying is that men know when women are menstruating, and they are aware of women who are exiled from the camp to the tent or who are otherwise marked out as separate by ritual taboo, and they will know, if archeology is any indication, what that means. Knowledge of female fertility is practically a mania in ancient civilizations. Second, the taboo has with it a proscription. From culture (and, of course, the evolutionary period is prior to material culture, so this is by implication only), we know that there is a time when the woman may not be touched and a time when the woman should be touched. Geogre 01:23, 10 Jul 2004 (UTC)
• Year-round sexual activity can be explained quite a bit more easily by the fact that humans have no single environment; they cannot be sure of famine or bounty conditions and therefore need to be able to mate at any time.
  • Neither do many other animals who do have seasonal sexual cycles. If feast/famine unpredictability were the driver, we would expect to see similar patterns in more of the species that share our range of environments. Rossami
    • Multiple births that take predation into account. Geogre 01:23, 10 Jul 2004 (UTC)
• Human infants are helpless for longer than any other young. They require complete attention for two to five years. Therefore, it is very important for there to be young, and it requires frequent mating to ensure reproduction. As complex organisms, humans are tenuous in utero, and human females produce a single child at a time.
  • Agreed. In fact, the article tries to argue that this is the cause of the evolutionary pressure toward concealed ovulation and its subsequent behavioral implications. Rossami
• Infant mortality in the evolutionary period would have been staggeringly high. After adding miscarriage into loss by predation, famine, and disease, you have all sorts of benefits to tricking not the male, but the female, into being pregnant year round.
  • Infant mortality is far higher in many other species, yet we do not see patterns of year-round fertility in those species. Even if it did, that does not explain the drive toward sex during times when the female's reproductive capacity is already being consumed (such as during the pregnancy and during breastfeeding-induced period of fertility suppression). Rossami
    • On the one hand, I refer back to the phenomenon of multiple births. The complexity of the human infant is such that women have difficulty with more than twinning, and young women are much less likely to twin than older women (suggesting an evolutionary adaptation to replacing the parents and older women being productive only in times of great bounty or dire need). I cannot explain sexual desire during times of unavailability, except that I would suggest that it's a non-maladaptive feature of the adaptive change of year-round fertiity. I.e. there is no simple biochemical way to turn it off, and it doesn't impair anything, so there is no advantage in developing a complex mechanism. N.b. society steps in where biology fails, and there are abundant examples of taboo, as well as fetish. Geogre 01:23, 10 Jul 2004 (UTC)
• Bonobo chimps have recreational sex. In fact, their sex (infamous for being same-sex as often as different sex) functions as a social bonding ritual, as an apology, a reassurance, and an erotic act.
  • True. This may be an argument that this evolutionary pattern developed somewhere in the primate tree if the Bonobo chimps also share the characteristics of long child-rearing leading to concealed ovulation. I've not seen a study one way or the other yet. Rossami
    • No. No one can say, yet, that I know of. The evidence, however, is in parallel, rather than line. The fact that these creatures have developed sex as social bond suggests that there are other possible explanations, not that we, or they, have inherited from one another. Can't social organization alone explain all the phenomena of "tough guy plants the seed and the nebbish loves the baby?" If so, there is no compelling need for resorting to an evolutionary explanation at all. Geogre 01:23, 10 Jul 2004 (UTC)
• Making blanket statements that "women prefer" is a generalization so broad as to stagger the imagination.
  • Agreed. Those comments should be fixed. Rossami
    • Bit of a cheap shot on my part, but an expression of frustration. Geogre 01:23, 10 Jul 2004 (UTC)
• Children look like their fathers to prevent infanticide? If alpha males are parenting but chump betas are rearing, wouldn't it be the dumbo beta who looks into the infant's eyes, sees the local bully, and then gets duped? How?
  • That theory was new to me (and, like everything else, had not been sourced by the original contributor). I can't really defend it. If we can't source it in a reasonable time, I'd support editing it out. Rossami
    • The logic on it loses me, as written. As a father of twins, all I noticed was that one looked like me, and one looked like her. Seven years on, one still looks a bit like me, one a bit like her. That's not scientific, of course, but I've always thought that babies were field onto which parents and grandparents projected the features of the parents. Geogre 01:23, 10 Jul 2004 (UTC)

• As this screed's original author, I assure you I'm not pushing Intelligent Design's crypto-Creationism. Intelligent design isn't needed to explain why woman whose ovulation is concealed; the screed attempts to explain causation entirely in mechanistic, evolutionary terms. -- orthogonal 00:34, 10 Jul 2004 (UTC)
  • No, no, I wasn't implying intelligent design. My problem is with evolutionary biology itself and how it can end up implying design. I don't encounter many evolutionary biologists explaining what's maladaptive about us. It seems to take something that is and then invite us to be clever in thinking up ways that it could be all for the best. For being a theory built upon naturalism, it ends up negating its impartiality, and my exasperation with the whole subject probably tempted me to greater irrascibility than was warranted. Geogre 01:23, 10 Jul 2004 (UTC)
    • I've read a few articles that slant toward the maladaptive features of the human knee and of human dietary urges. (Frankly, I've always considered the knee as incontrovertible proof against intelligent design. Even a freshman engineer could design a better joint.) But you're right that the most of the articles use anthropomorphism a little too liberally. Rossami

---

Some answers to the objection that women know when they menstruate, so therefore ovulation is not concealed. Of course, it's once again from Slashdot and ex tempore:

I certainly don't need a lab test to know when my period is coming. Just because women apparently conceal from you when they're menstruating that doesn't mean that we don't know.

Yes, but ovulation is not menstruation (getting one's "period"). Ovulation occurs about fourteen days before menstruation, and the period of fertility is some period of time a up to five days before ovulation and one to two days after ("fertile" days can occur before actual ovulation because sperm can live inside a woman for up to a week).

While menstruation pretty reliably occurs fourteen days after ovulation, the time between menstruation and the next ovulation tends to vary much more.

So while your menstruation is pretty obvious, it gives you little idea of when you'll next be fertile.

And while some women feel a characteristic pain when ovulation occurs ("Mittelschmerz", German for "middle pain"), because of the varying time between menstruation and ovulation and the ability of sperm to live inside the women, it's entirely possible even for that minority of women who experience Mittelschmerz to become pregnant from sex after menstruation but before ovulation and the warning pain of Mittelschmerz.

You do know what the technical medical term for a woman who relies on the "rhythm method" of contraception is?

"Mother". -- orthogonal 00:46, 10 Jul 2004 (UTC)

• • Oh, quite. I just note that we keep digging up these calendars and fertility figures, and it seems like the fertile woman was an object of intense interest to our ancestors, who needed to be very curious on the subject if they wished to have a tribe for very long. Today, with our hygiene and scents and clothing and air conditioning, fertility is quite mysterious, and we go off and spend money on sticks to push into urine flow. I wonder if any of us can conceive (sorry) of how much plainer it would have been in a tribal setting. Geogre 01:23, 10 Jul 2004 (UTC)

Concealed ovulation is a short sighted theory, sadly still very supported, that is very hardly refused by the very fact of menstruation itself. Menstruation evolved much earlier than humanity, and it ocurres in other primates. It is hard to conceal the reproductive cycle when the female gets its menstrual discharge at the end of the same. --Pedro Lamo (talk) 05:53, 23 May 2017 (UTC)

Sustainability issue

There is a sustainability paradox with the theory dividing alpha and beta male reproductive classifications. Follow the logic:

• The reproductive classification is genetically determined by means of a hormone, testosterone. Whether a male will be an alpha or beta male correlates to the status of his biological father, rather than the male by whom he was raised.
• If a son is raised by a beta male but was actually fathered by an alpha male who (surreptitiously) impregnated the mother, as an adult the son will pursue an r-selecting reproductive strategy like that of his true biological father, even though this biological father was not involved in his rearing.
• This benefits the mother, because the alpha-male son propagates her genetic material.
• It is a disadvantage to the beta male, who raises others' offspring but does not have a chance to reproduce himself.
• Eventually the sustainability crisis comes. The beta males become less and less. There are simply the alpha males who are trying to have someone else raise their offspring.
• There are no beta males left. The shebang falls apart.
• Therefore there is a flaw in the theory.

concealed ovulation was a side effect

I think that we have to look at concealed ovulation in humans and ask us how it evolved and what the steady state was before rather than what purpose it serves. A common mistake is to compare signalled ovulation and compare it with concealed ovulation and then trying to find advantages with the latter.

I can’t see any evolutionary advantage in concealing ovulation. That is, if there is an obvious sign that makes the male sexually interested in the female it would be counterproductive to remove that sign – the female would not reproduce.

If we put the female in a context where she can influence whom to mate with, being sexually attractive could be advantageous. The female would bee wooed possibly by many males. This could result in gifts of food and other possible favours. When the sign is not present these advantages would be lost. Thus extending the sign past the actual fertile period could result in more favours and more food. However, when the sign is in place during the whole cycle it eventually looses its value (but that is an evolutionary process in itself to study and the signal could be reinforced rather than vanish).

Eventually another random variation correlating with the fertile period could become detectable by males through evolution and another period of advertised ovulation could start.

For me this is the most probable explanation of “concealed” ovulation – the question is what the signal used to be and if it is still present or if, after loosing its value, it disappeared.

It is of course also interesting to see what consequences concealed ovulation has on the social structure. But the consequences on the social structure in the new steady state (when all females signal fertility during the whole cycle and sensitivity to a new signal has not evolved) would not be necessary or even relevant to explain how it evolved.

((Breasts do differ in size during the cycle (however not being at the largest state whilst the female is the most fertile, but this might be a more recent change). This could be a reason for the excessive interest in breasts that males tend to show (there are other conceivable reasons to). However, this is just speculation.)) Erilu

I moved this from the front page to this page. Please use the talk page for discussions --- ZacBowling

Footnotes

The following section was removed from the article at 19:22, 8 September 2006.

Discussion of the claim that women do not know when they are fertile

The claim that many women do not know when they are fertile is disputed. Awareness of the relationship between menstrual cycles and fertility has been documented even in aboriginal societies. Some also dispute this claim on the theory that pheromone sensitivity is high enough to reach conscious levels in pre-industrial societies because of increased and continuous proximity, absence of chemical agents used in personal hygiene, and in some cases a warm/tropical or subtropical climate (since warmer air carries suspended substances more readily). Also typically involved in such pre-industrial warm-climate environments is a low total area cm2 of clothing over the average woman. This would allow the pheromone to drift or broadcast freely from the fertile female, signalling all males in proximity that she is ready to be impregnated. This would imply that rather than having no way of knowing when ovulation occurs, men would be alerted of it by the pheromones put off by relatively uncovered fertile women. (The pheromone is secreted during the fertile part of a female's menstrual cycle, and especially during ovulation, by specialised apocrine glands located mostly in the woman's pubic region and the lower part or 'small' of her back (lordosis), as well as being sparsely throughout the body surface). In developed societies today in most cases, the intensity of pheromonal output from an ovulating woman would be only enough to influence someone extremely and consistently close to her, such as her husband. Recent Mexican and U.S. research has been studying the phenomenon in which some husbands, who have been part of programs in which couples chart the cycle for purposes of "family planning" or trying to conceive, report eventually being able to perceive when their wives are fertile, while finding it difficult to articulate why.

The lag time between menstruation and fertility complicates the other objection, that menstruation is the marker signal (a visible sign). As evidence of the difficulty of relating menstrual cycles with fertility, variations on the following joke have been found in many cultures: "What is the medical term for a woman who relies only on the Rhythm Method for birth control? A mother.", or similar jokes intended as insults against the Roman Catholic Church. Some observational methods of fertility awareness, however, can have failure rates of less than 1% per year. While fertility is not intuitive to most women, the signs are simple enough almost any woman can be taught them.

Another externally detectable signal of female fertility is the observable set of changes in the mammae of the woman just before she ovulates. Observation of this fertility signal, however, is possible only with direct touch or very close proximity. Pheromonal release, however, can be picked up from a further distance, and through respiration. This characteristic means that pheromones could attract r-selecting males to an ovulating female. It would also be harder for the beta male (as described in the theory earlier) to prevent r-selecting males from inseminating the woman, because they can detect signs of her fertility. The pheromonal signal is also more accurate. Release of the pheromone from a woman reliably indicates that any spermatozoa injected into the woman's reproductive system at the time will likely have a chance to fertilise her ovum.

Also, the greatest incentive for the pair bond is agriculture. The parents need each other to sustain the agricultural establishment. This would mean that they stay with each other, and consequently raise their children together. A man in an agricultural society generally cannot simply inseminate a fertile woman and have no association with her after that; he must stay because he needs the woman's steady support. Therefore the man is present to raise the children that he fathers. In the hunter-gatherer model the woman was dependent on the man but not vice versa; agriculture balances the stick by making the man dependent on the woman as well. It also prevents any man from reproducing without having to invest himself in parenting. (Even today, rural societies that engage in agriculture tend to have more monogamy than extant hunting-gathering societies in the same regions of the world.)

Another unresolved issue is what used to be the signal, if there was a signal, for ovulation prior to the state of concealed ovulation in human evolutionary history. If there was a signal, how did it disappear? A possible explanation is that it was signaled for longer and longer periods outside of the actual fertility period. Eventually the signal was active during the whole cycle, thus loosing its predictive effect.

Hence there are many objections to the theories elaborated upon at the beginning of this page. Another explanation is that relatively concealed ovulation (if it even really exists in the indigenous environment) is actually due to the pair bonding scheme and not the other way around. In an exclusive pair bonding situation it would not be desirable to advertise one's fertility to men other than one's partner. Signals of ovulation would be of benefit only if they could be discerned solely by the female's one male partner. Such appears often to be the case with the ovulation-correspondent pheromone in studies done in many modern countries; the debate is whether this extends to indigenous environments, of which little research has been done. For reasons detailed earlier, it appears that in some indigenous societies the pheromonal indicator is easily perceived by all men in proximity, although very little study has been done. In that case a man would be able to take advantage of this reproductive opportunity by making the woman pregnant with his offspring. The likelihood that a man would have the inclination to do that, and that she would allow him to, are matters for further research and debate. It is unlikely that a large majority of the scientific community will agree on these disputes anytime soon.

agriculture and nutrition

"Until the beginnings of agriculture, breastfeeding and low nutrition levels caused a natural fertility suppression."

that's from the wiki. in fact, studies (jared diamond) show exactly the opposite: the advent of agriculture correlated with a drop in nutrition and health. done successfuly, agriculture can guarantee "bulk" in a particular region, but not nutrition, since it doesn't inherently have any nutritional benefits. it's a totally unsubstantiated argument. —The preceding unsigned comment was added by 128.119.132.224 (UTC) (talk • contribs) 19:45, 16 October 2006 (UTC)

Not only that, but the sentence implies that breastfeeding stopped when agriculture started (!)

If you are interested and have some knowledge of the topic, please be bold and edit the page. Lyrl ^Talk _Contribs 21:33, 16 October 2006 (UTC)

Proposed merge

The entry entitled 'Menstruation and the origins of culture' is fundamentally about the evolutionary emergence of symbolic culture. It would not be helpful to place it under 'concealed ovulation', which is a purely biological topic. Agreed that 'concealed ovulation' in Wikipedia is not accurate or authoritative as it stands. Totally unclear what Engels has got to do with it, for example (I say this as an admirer of Engels) But I do agree with the suggestion that the material on concealed ovulation currently in 'menstruation and the origins of culture' might usefully be merged in some way with 'concealed ovulation'. Will try to update the concealed ovulation entry with proper scholarly references later this week. Chris 86.136.13.247 09:56, 20 August 2006 (UTC)

Page needs cleanup

When discussing concealed ovulation it is pointless to compare concealed to signalled ovulation. One must start the discussion with - what would be the consequences of a signal that is on longer than actual fertility and one that is on shorter than actual fertility - evolution dos not seek a state if the road there is not for the better - what good is half a wing... this page needs a restructuring!

First of all which road to concealed ovulation did humans walk. Was the signal on for ever longer or ever shorter periods of time? (or possibly did the signal slowly fade and became ever harder to detect). Ever longer would infer that the signal eventually encompassed the whole cycle and then became pointless.

According to me this is the interesting unresolved issue concerning concealed ovulation. Erilu 02:40, 12 December 2006

Non-obvious wikilinks in "see-also" section

An editor has recently added infanticide (zoology) and self-deception to the "see also" section of this article. I had reverted the infanticide link not understanding how it was related to this article, and it was restored with advice that I read a particular book. I have no idea how influential this book or the ideas it presents are in the related science fields - the Wikipedia article on the book doesn't seem to meet the requirements of WP:N, which could indicate either the book not being important to the field or nobody having gotten around to improving the Wikipedia article to that point.

But if I have to read a book to understand how a concept is related, maybe it's not sufficiently closely related to be in a see-also section. I find it very bizarre to see both of these links there, and skimming through the Wikipedia articles on those two topics I found no information related to concealed ovulation. If I'm interested in learning about concealed ovulation, why would I want to read those two Wikipedia articles?

Also, I don't believe "see also" links should be piped. Piping the animal infanticide article to look like the link is to the human infanticide article just adds to the eerie feeling having that link in this article gives me. Lyrl^Talk _C 14:42, 11 January 2008 (UTC)

Diamond describes the research of others in that area (and the book is notable, though needs a reception section). Basically there are two hypotheses for the evolution of concealed ovulation, one of them involving infanticide as the "selective pressure". The article on infanticide still doesn't have anything on concealed ovulation either, I just haven't had much time to edit these articles and too few others write on evolutionary theory. Linking to the human infanticide article would be pretty useless, as it doesn't go into evolution at all. Richard001 (talk) 10:25, 20 March 2008 (UTC)

Thank you for the reply. I'll look forward to seeing the link return to this article when the infanticide article gets expanded to include more evolutionary theory. Lyrl^Talk _C 01:25, 21 March 2008 (UTC)

Estrus(?) vs Menstruation

The article seems to confuse estrus/estrous/oestrus (see appropriate article for discussion on spelling!) with menstruation. Humans don't have an oestrus cycle, they menstruate. Darmot and gilad (talk) 13:20, 29 January 2008 (UTC)

Baboons have an oestrus cycle AND menstruate. The two characteristics are not mutual exclusive. Also, there are researchers who claim that humans do have an estrus (thus the studies claiming fertile women are more attractive). Lyrl^Talk _C 01:25, 21 March 2008 (UTC)

• User:Darmot and gilad, I hope that you are asexual and reproduce through cell division, because otherwise you are in serious trouble... Human women have both a menstrual and an ovulatory cycle that overlap - that is probably the reason for the confusion that you perceive... As Lyrl notes above, much of the research that has come out in the last 10 years supports and argues in favor of a female human estrus cycle. The debate is not so much whether it happens, but whether it is perceptible and whether it affects human behavior or not and to what extent... Stevenmitchell (talk) 09:42, 6 November 2009 (UTC)

talk, that pun to Darmot and gilad was unneccesary as well as not documented. Here you have how Wikipedia describes differences betweenestrous and menstrual cycles: "Mammals share the same reproductive system, including the regulatory hypothalamic system that releases gonadotropin releasing hormone in pulses, the pituitary that secretes follicle stimulating hormone and luteinizing hormone, and the ovary itself that releases sex hormones including estrogens and progesterone.

However, species vary significantly in the detailed functioning. One difference is that animals that have estrous cycles reabsorb the endometrium if conception does not occur during that cycle. Animals that have menstrual cycles shed the endometrium through menstruation instead. Another difference is sexual activity. In species with estrous cycles, females are generally only sexually active during the estrus phase of their cycle (see below for an explanation of the different phases in an estrous cycle). This is also referred to as being "in heat". In contrast, females of species with menstrual cycles can be sexually active at any time in their cycle, even when they are not about to ovulate.

Humans have menstrual cycles rather than estrous cycles. They, unlike other species, were thought to not have any obvious external signs to signal estral receptivity at ovulation (concealed ovulation). Some research suggests, however, that women tend to have more sexual thoughts and are far more prone to sexual activity right before ovulation (estrus).[1][2]]"

The fact is that the vision of cycles is changing in the light of the last discoveries of menstruation in many species, and probably in a short time we'll see a redefinition of the concepts of estrous and menstrual cycles. --Pedro Lamo (talk) 06:00, 23 May 2017 (UTC)

Who Cut Out Most of This Article?

This article used to be a fairly extensive article - now it is a little stub... Who did all the cutting and why? Stevenmitchell (talk) 09:46, 6 November 2009 (UTC)

The old version of the article is here. It was completely unreferenced. Much of the "Engels" and "discussion" sections were unrelated to the title of the article. The current article is shorter, but well-referenced and tightly on topic: a large improvement, in my opinion. Lyrl^Talk _C 17:49, 8 November 2009 (UTC)

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