6 ms·

Why do women have periods when most animals don't?

80 points by dataminer 11y ago

ripter 11y ago
> It seems the list of animals that menstruate is quite short: humans, apes, monkeys, bats and elephant shrews. What do these seemingly disparate animals have in common? My unfixed female dogs have periods. So either the article is poorly written, or they are ignoring animals that don't fit the theory.
- toast0 11y ago
  > So either the article is poorly written The headline is (extra apostrophe), so I'd assume the article is too. :)
  - rosser 11y ago
    The article's headline doesn't have the apostrophe.
- rosser 11y ago
  Dogs don't have periods; they have estrous, commonly called "heat". https://en.wikipedia.org/wiki/Estrous_cycle https://en.wikipedia.org/wiki/Estrous_cycle - note specifically #Differences_from_the_menstrual_cycle
  - mturmon 11y ago
    Thanks. If people really want the one-sentence version: "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." This is discussed in the OP at some length. Alas, the grandparent comment is something of a middlebrow dismissal.
  - ripter 11y ago
    Dogs bleed. It might not be a 'period', but the article is talking about why some animals bleed and most don't.
    - rosser 11y ago
      Well, if you're going to attempt to be pedantic about it, the word "bleeding" isn't exactly correct to begin with. The discharge is endometrial tissue, not blood.
      - ripter 11y ago
        Before calling names, let's look at the article in detail. "Of course, I wasn't the only one: most women menstruate. But most other female animals don't bleed outwardly like us. Even among those that give birth to live young as we do, only a handful of species menstruate." So the term menstruate is used to mean to "bleed outwardly like us". "If the woman doesn't get pregnant, progesterone levels begin to fall. The thick endometrial tissue with its blood vessels then begins to slough off, and passes out through the vagina. This bleeding is menstruation." So they are expanding on the term menstruate. Now it's both "bleed outwardly like us" and "The thick endometrial tissue with its blood vessels then begins to slough off, and passes out through the vagina" "On average, women lose 30 to 90 ml of fluid over 3-7 days of menstruation. We know, because scientists have given women pre-weighed pads and tampons, and weighed them again after use." Clarifying the term menstruate and showing how to measure it. I'm going to paraphrase the definition of the term. So at this point, when they talk about menstruation, they are talking about a blood like fluid, that can be measured, and that happens when the the tissue and blood vessels pass out of the vagina. The article has a break to talk about the history, theories, and research that has happened over the years. After that they get to the main point. "To figure out the truth, we need to compare animals that do and don't menstruate." "Great apes do it too. Menstrual bleeding is easily detectable in chimpanzees and gibbons. However, gorillas and orang-utans bleed less copiously, so menstruation is only visible on closer inspection. Other primates, such as tarsiers, may also menstruate, but there is little hard evidence." They re-iterate key parts of the term. When this article talks about menstruation, they are specifically talking about detectable bleeding. Now we can get to the heart of my objection. They spent most of the article defining their usage of the term menstruation, and how it relates to the research. The article claims "It seems the list of animals that menstruate is quite short: humans, apes, monkeys, bats and elephant shrews. What do these seemingly disparate animals have in common?", remember the definition they use for menstruate, blood and tissue passing though the vagina. If you've ever owned an unfix female dog during heat, you'll be quite aware that they do, in fact bleed out their vagina for a period of time during their reproductive cycle. This fits with their definition. The only mention of dogs is: "In dogs and cats, the foetuses dig in a little more. But in humans and other primates, a foetus will dig through all the womb lining to directly bathe in its mother's blood." This does not specify why dogs do not fit into their term. In fact this seems to support that dogs have a very similar cycle to humans. So my question remains, Why are dogs excluded? They never acknowledge the contradiction. So either the article incorrectly sets up the terms, or they don't want to talk about dogs because it doesn't fit the narrative.
- swagasaurus-rex 11y ago
  Before my dog was fixed, we had to buy little doggie diapers once a year so she wouldn't bleed all over the house. I am, therefore, a little confused over the article.
daktanis 11y ago
Weird thing for hacker news
- dreamdu5t 11y ago
  Downvoted but you have a point. Why is there no moderation with regards to topical content on HN? Why should HN be a place for pop-sci articles and repostings from the likes of the Economist, LA Times, BBC, etc. r/startups has more content pertaining to - you know - actually starting a technology business than HN does. HN lately reads like newsclippings sent to me by my grandma.
  - stcredzero 11y ago
    Why is there no moderation with regards to topical content on HN? As per the posted policy when I joined HN, this would have been topical. (It has changed since.) "Anything that would be interesting to hackers." I don't mind at all if the occasional pop-sci article comes by, so long as they don't all do so unfiltered. Ironically, this comment and the one it replies to are distinctly against the moderation policy, as per my understanding.
    - dang 11y ago
      > It has changed since. How? I don't recall any change. Or are you referring to Startup News, the predecessor of HN?
      - stcredzero 11y ago
        Once upon a time, we weren't supposed to downvote to disagree. Then there was a capitulation, IIRC, and that became kosher. Now, I think things may be back to where we started. I don't keep miniscule track of changes to the moderation policy. (Maybe I should?)
  - jacquesm 11y ago
    A glance at the homepage makes me wonder if your grandma is a former co-worker of Grace Hopper or something like that.
derefr 11y ago
tl;dr: What we know for sure: foetuses produce hormones to keep the endometrial tissue from thinning. Once a zygote has implanted, the mother's hormones are thus no longer in control of whether her uterus will support its growth or not. Menstruation, when it happens, forcefully cleans out implanted zygotes, returning the uterine hormonal balance to normal. What we guess that that implies: menstruation is a side-effect of enabling spontaneous abortion (miscarriage) of a still-live foetus, thus allowing females of those species to not have to go through the "avoid males you're not interested in during estrus" dance that most animals do. This confers social advantages. In humans specifically, estrus is hidden completely from both male and female awareness. This confers further social advantages, but only could have evolved to fixation if the sexual-selection advantage of applying a "proximity during estrus" filter was completely outmoded/obviated by miscarriage.
- johncs 11y ago
  There were a few explanations proposed. This was one of them, but it was unclear if this is the theory with the most support.
- ars 11y ago
  The problem with that theory is I don't know of any women who are actually able to miscarry at will. A garbled version of that theory got some politicians in hot water with the whole "during rape, their body can shut it down" comment.
  - dhimes 11y ago
    Agree. I've seen ability to orgasm linked to selectivity for fertilization, as the speculation (I don't follow it enough to know if it is a theory or not in any allowable sense of the word) is that (female) orgasm during intercourse helps the sperm reach the egg.
  - Jun8 11y ago
    It doesn't have to be "at will", our bodies do a lot of processing without us being consciously aware of it. I think it is well within reason that the body may detect an abnormal embryo and respond to it.
amyjess 11y ago
Am I the only one bugged by the apostrophe in "animal's"?
- dhimes 11y ago
  No. Looks like we posted at the same time.
- herbig 11y ago
  I'm more curious as to whether the original article was published with an apostrophe, or the HN poster actually typed the title out from memory rather than cut/paste.
dhimes 11y ago
Please fix the apostrophe in "animal's" It is annoying and leads non-native speakers on the board astray. Thank you. To non-native speakers: apostrophes are for possession, not plural.
- jacquesm 11y ago
  > To non-native speakers: apostrophes are for possession, not plural. You could easily repeat that for plenty of native speakers. It's one of the most common mistakes in written English.
  - profinger 11y ago
    Isn't it sad? It's such a frustrating mistake. There's a bar that we drive past frequently that does it with everything. They're "Now accepting application's" and their "Burger's are $2" Sad.
    - CartyBoston 11y ago
      Wait ... where is there a $2 burger?
    - drostie 11y ago
      Since I moved to Missouri, I've been upset by a similar grammatical error: quotation marks used for emphasis. You would expect, say, all-capitals or an underline or italics, but you instead see 'Come taste the "best" burger in Missouri,' which is awful. In New York, where I grew up, that use of quotation marks is called "scare quotes": quotation marks in all cases signal that you're detaching a text fragment from its context; with scare quotes you detach a phrase which reads just fine in that context to either bring focus to the phrase (like when you're defining it) or to indicate that the phrase itself is somehow problematic (like when you want to criticize the phrase, e.g. 'these "businessmen" are stealing our money,' where you're implying that they are either not truly men or not truly doing business per se.) When you say that you have 'the "best" burger', to me it sounds like you're implicitly adding at the end, 'well, at least, it's the best at being an awful burger.'
ttflee 11y ago
A little OT, but I am always tempted to think whether the lunar calendar has something to do with menstruation or not.
ars 11y ago
To answer in short: No one knows. All sorts of theories in the article, none with any real evidence, except "this makes sense to me".
agdalrymple 11y ago
Why are you posting this on HN? Crawl back to your cave.
deleted 11y ago
[deleted]
madez 11y ago
There is a highly complex biochemical relationship between the embryo and the mother. The mother actively tries to kill anything that might be in her uterus, she even periodically cleans her uterus radically by ejecting a layer of it. The embryo needs to produce hormones that manipulate the mother to stop that, and deliver them into the mother. If the embryo fails, it dies. Source: http://aeon.co/magazine/science/pregnancy-is-a-battleground-between-mother-father-and-baby/ http://aeon.co/magazine/science/pregnancy-is-a-battleground-... We do something similar in software development. If our program experiences a segfault, we usually let it die, instead of figuring out at runtime what went wrong and trying to do what we still can do. Then we change something and try again. Making it hard for the embryo in the beginning and starting over if it didn't make it, is the biological equivalent to that strategy. It might result in a heuristic whether it's worth investing more resources in it. Saving resources gives an evolutionary advantage. On the other hand, it makes evolutionary progress harder since more conformity of the embryo is a condition to survive.
acqq 11y ago
"most animals don't"? What do they mean? Dogs definitely do have a kind of "bleeding" as (hopefully) any dog owner knows. https://answers.yahoo.com/question/index?qid=20060612224917AADVpCu https://answers.yahoo.com/question/index?qid=20060612224917A... It's however not "the same" as the one in primates: http://en.wikipedia.org/wiki/Menstruation_%28mammal%29 http://en.wikipedia.org/wiki/Menstruation_%28mammal%29 "Some species, such as domestic dogs, experience small amounts of vaginal bleeding while in heat; this discharge has a different physiologic cause than menstruation." And if we talk about "periods" (like in the article title) and not just "bleeding," the fertility "periods" are everywhere. http://en.wikipedia.org/wiki/Spawn_%28biology%29 http://en.wikipedia.org/wiki/Spawn_%28biology%29 Even corals have spawn cycles. Most animals do have fertility "periods" they just don't bleed. But again, we are primates, and a lot of primates do have the same menstruation that the humans have. So humans certainly aren't special in that aspect.
- itsybitsycoder 11y ago
  So you agree that most animals don't menstruate... what's wrong with the article's title? EDIT: Oh, I think I get it now. "Period" in this context does not refer to the general fertility cycle. It is specifically a euphemism for menstruation. That is why you'll hear people saying things like "I'm on my period", "my period started late/early", etc. These phrases would not make sense if it referred to the fertility cycle in general, since from puberty to menopause, most healthy women are in some phase of a fertility cycle.
  - acqq 11y ago
    Yes, and even if the topic is just bleeding, humans aren't special, so it still shouldn't be "why do women bleed" but "why just primates, bats and one kind of shrew bleed during estrous cycle." Humans simply aren't special in that regard. And the whole "mystery" doesn't appear so dramatic anymore. It becomes obvious that that "optimization" developed more than once.

80 points by dataminer 11y ago

> It seems the list of animals that menstruate is quite short: humans, apes, monkeys, bats and elephant shrews. What do these seemingly disparate animals have in common? My unfixed female dogs have periods. So either the article is poorly written, or they are ignoring animals that don't fit the theory.

toast0 11y ago
> So either the article is poorly written The headline is (extra apostrophe), so I'd assume the article is too. :)
- rosser 11y ago
  The article's headline doesn't have the apostrophe.
rosser 11y ago
Dogs don't have periods; they have estrous, commonly called "heat". https://en.wikipedia.org/wiki/Estrous_cycle https://en.wikipedia.org/wiki/Estrous_cycle - note specifically #Differences_from_the_menstrual_cycle
- mturmon 11y ago
  Thanks. If people really want the one-sentence version: "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." This is discussed in the OP at some length. Alas, the grandparent comment is something of a middlebrow dismissal.
- ripter 11y ago
  Dogs bleed. It might not be a 'period', but the article is talking about why some animals bleed and most don't.
  - rosser 11y ago
    Well, if you're going to attempt to be pedantic about it, the word "bleeding" isn't exactly correct to begin with. The discharge is endometrial tissue, not blood.
    - ripter 11y ago
      Before calling names, let's look at the article in detail. "Of course, I wasn't the only one: most women menstruate. But most other female animals don't bleed outwardly like us. Even among those that give birth to live young as we do, only a handful of species menstruate." So the term menstruate is used to mean to "bleed outwardly like us". "If the woman doesn't get pregnant, progesterone levels begin to fall. The thick endometrial tissue with its blood vessels then begins to slough off, and passes out through the vagina. This bleeding is menstruation." So they are expanding on the term menstruate. Now it's both "bleed outwardly like us" and "The thick endometrial tissue with its blood vessels then begins to slough off, and passes out through the vagina" "On average, women lose 30 to 90 ml of fluid over 3-7 days of menstruation. We know, because scientists have given women pre-weighed pads and tampons, and weighed them again after use." Clarifying the term menstruate and showing how to measure it. I'm going to paraphrase the definition of the term. So at this point, when they talk about menstruation, they are talking about a blood like fluid, that can be measured, and that happens when the the tissue and blood vessels pass out of the vagina. The article has a break to talk about the history, theories, and research that has happened over the years. After that they get to the main point. "To figure out the truth, we need to compare animals that do and don't menstruate." "Great apes do it too. Menstrual bleeding is easily detectable in chimpanzees and gibbons. However, gorillas and orang-utans bleed less copiously, so menstruation is only visible on closer inspection. Other primates, such as tarsiers, may also menstruate, but there is little hard evidence." They re-iterate key parts of the term. When this article talks about menstruation, they are specifically talking about detectable bleeding. Now we can get to the heart of my objection. They spent most of the article defining their usage of the term menstruation, and how it relates to the research. The article claims "It seems the list of animals that menstruate is quite short: humans, apes, monkeys, bats and elephant shrews. What do these seemingly disparate animals have in common?", remember the definition they use for menstruate, blood and tissue passing though the vagina. If you've ever owned an unfix female dog during heat, you'll be quite aware that they do, in fact bleed out their vagina for a period of time during their reproductive cycle. This fits with their definition. The only mention of dogs is: "In dogs and cats, the foetuses dig in a little more. But in humans and other primates, a foetus will dig through all the womb lining to directly bathe in its mother's blood." This does not specify why dogs do not fit into their term. In fact this seems to support that dogs have a very similar cycle to humans. So my question remains, Why are dogs excluded? They never acknowledge the contradiction. So either the article incorrectly sets up the terms, or they don't want to talk about dogs because it doesn't fit the narrative.
swagasaurus-rex 11y ago
Before my dog was fixed, we had to buy little doggie diapers once a year so she wouldn't bleed all over the house. I am, therefore, a little confused over the article.

daktanis 11y ago

Weird thing for hacker news

dreamdu5t 11y ago
Downvoted but you have a point. Why is there no moderation with regards to topical content on HN? Why should HN be a place for pop-sci articles and repostings from the likes of the Economist, LA Times, BBC, etc. r/startups has more content pertaining to - you know - actually starting a technology business than HN does. HN lately reads like newsclippings sent to me by my grandma.
- stcredzero 11y ago
  Why is there no moderation with regards to topical content on HN? As per the posted policy when I joined HN, this would have been topical. (It has changed since.) "Anything that would be interesting to hackers." I don't mind at all if the occasional pop-sci article comes by, so long as they don't all do so unfiltered. Ironically, this comment and the one it replies to are distinctly against the moderation policy, as per my understanding.
  - dang 11y ago
    > It has changed since. How? I don't recall any change. Or are you referring to Startup News, the predecessor of HN?
    - stcredzero 11y ago
      Once upon a time, we weren't supposed to downvote to disagree. Then there was a capitulation, IIRC, and that became kosher. Now, I think things may be back to where we started. I don't keep miniscule track of changes to the moderation policy. (Maybe I should?)
- jacquesm 11y ago
  A glance at the homepage makes me wonder if your grandma is a former co-worker of Grace Hopper or something like that.

derefr 11y ago

tl;dr: What we know for sure: foetuses produce hormones to keep the endometrial tissue from thinning. Once a zygote has implanted, the mother's hormones are thus no longer in control of whether her uterus will support its growth or not. Menstruation, when it happens, forcefully cleans out implanted zygotes, returning the uterine hormonal balance to normal. What we guess that that implies: menstruation is a side-effect of enabling spontaneous abortion (miscarriage) of a still-live foetus, thus allowing females of those species to not have to go through the "avoid males you're not interested in during estrus" dance that most animals do. This confers social advantages. In humans specifically, estrus is hidden completely from both male and female awareness. This confers further social advantages, but only could have evolved to fixation if the sexual-selection advantage of applying a "proximity during estrus" filter was completely outmoded/obviated by miscarriage.

johncs 11y ago
There were a few explanations proposed. This was one of them, but it was unclear if this is the theory with the most support.
ars 11y ago
The problem with that theory is I don't know of any women who are actually able to miscarry at will. A garbled version of that theory got some politicians in hot water with the whole "during rape, their body can shut it down" comment.
- dhimes 11y ago
  Agree. I've seen ability to orgasm linked to selectivity for fertilization, as the speculation (I don't follow it enough to know if it is a theory or not in any allowable sense of the word) is that (female) orgasm during intercourse helps the sperm reach the egg.
- Jun8 11y ago
  It doesn't have to be "at will", our bodies do a lot of processing without us being consciously aware of it. I think it is well within reason that the body may detect an abnormal embryo and respond to it.

amyjess 11y ago

Am I the only one bugged by the apostrophe in "animal's"?

dhimes 11y ago
No. Looks like we posted at the same time.
herbig 11y ago
I'm more curious as to whether the original article was published with an apostrophe, or the HN poster actually typed the title out from memory rather than cut/paste.

dhimes 11y ago

Please fix the apostrophe in "animal's" It is annoying and leads non-native speakers on the board astray. Thank you. To non-native speakers: apostrophes are for possession, not plural.

jacquesm 11y ago
> To non-native speakers: apostrophes are for possession, not plural. You could easily repeat that for plenty of native speakers. It's one of the most common mistakes in written English.
- profinger 11y ago
  Isn't it sad? It's such a frustrating mistake. There's a bar that we drive past frequently that does it with everything. They're "Now accepting application's" and their "Burger's are $2" Sad.
  - CartyBoston 11y ago
    Wait ... where is there a $2 burger?
  - drostie 11y ago
    Since I moved to Missouri, I've been upset by a similar grammatical error: quotation marks used for emphasis. You would expect, say, all-capitals or an underline or italics, but you instead see 'Come taste the "best" burger in Missouri,' which is awful. In New York, where I grew up, that use of quotation marks is called "scare quotes": quotation marks in all cases signal that you're detaching a text fragment from its context; with scare quotes you detach a phrase which reads just fine in that context to either bring focus to the phrase (like when you're defining it) or to indicate that the phrase itself is somehow problematic (like when you want to criticize the phrase, e.g. 'these "businessmen" are stealing our money,' where you're implying that they are either not truly men or not truly doing business per se.) When you say that you have 'the "best" burger', to me it sounds like you're implicitly adding at the end, 'well, at least, it's the best at being an awful burger.'

ttflee 11y ago

A little OT, but I am always tempted to think whether the lunar calendar has something to do with menstruation or not.

ars 11y ago

To answer in short: No one knows. All sorts of theories in the article, none with any real evidence, except "this makes sense to me".

agdalrymple 11y ago

Why are you posting this on HN? Crawl back to your cave.

deleted 11y ago

[deleted]

madez 11y ago

There is a highly complex biochemical relationship between the embryo and the mother. The mother actively tries to kill anything that might be in her uterus, she even periodically cleans her uterus radically by ejecting a layer of it. The embryo needs to produce hormones that manipulate the mother to stop that, and deliver them into the mother. If the embryo fails, it dies. Source: http://aeon.co/magazine/science/pregnancy-is-a-battleground-between-mother-father-and-baby/ http://aeon.co/magazine/science/pregnancy-is-a-battleground-... We do something similar in software development. If our program experiences a segfault, we usually let it die, instead of figuring out at runtime what went wrong and trying to do what we still can do. Then we change something and try again. Making it hard for the embryo in the beginning and starting over if it didn't make it, is the biological equivalent to that strategy. It might result in a heuristic whether it's worth investing more resources in it. Saving resources gives an evolutionary advantage. On the other hand, it makes evolutionary progress harder since more conformity of the embryo is a condition to survive.

acqq 11y ago

"most animals don't"? What do they mean? Dogs definitely do have a kind of "bleeding" as (hopefully) any dog owner knows. https://answers.yahoo.com/question/index?qid=20060612224917AADVpCu https://answers.yahoo.com/question/index?qid=20060612224917A... It's however not "the same" as the one in primates: http://en.wikipedia.org/wiki/Menstruation_%28mammal%29 http://en.wikipedia.org/wiki/Menstruation_%28mammal%29 "Some species, such as domestic dogs, experience small amounts of vaginal bleeding while in heat; this discharge has a different physiologic cause than menstruation." And if we talk about "periods" (like in the article title) and not just "bleeding," the fertility "periods" are everywhere. http://en.wikipedia.org/wiki/Spawn_%28biology%29 http://en.wikipedia.org/wiki/Spawn_%28biology%29 Even corals have spawn cycles. Most animals do have fertility "periods" they just don't bleed. But again, we are primates, and a lot of primates do have the same menstruation that the humans have. So humans certainly aren't special in that aspect.

itsybitsycoder 11y ago
So you agree that most animals don't menstruate... what's wrong with the article's title? EDIT: Oh, I think I get it now. "Period" in this context does not refer to the general fertility cycle. It is specifically a euphemism for menstruation. That is why you'll hear people saying things like "I'm on my period", "my period started late/early", etc. These phrases would not make sense if it referred to the fertility cycle in general, since from puberty to menopause, most healthy women are in some phase of a fertility cycle.
- acqq 11y ago
  Yes, and even if the topic is just bleeding, humans aren't special, so it still shouldn't be "why do women bleed" but "why just primates, bats and one kind of shrew bleed during estrous cycle." Humans simply aren't special in that regard. And the whole "mystery" doesn't appear so dramatic anymore. It becomes obvious that that "optimization" developed more than once.