Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Iraq war over population control?

  1. Jan 23, 2007 #1
    i was just reading about chinas 1.4 boy to girl birth ratio and it has me wondering is this going on in the united states? it seems to me like finding the right girls has always been a fight. shotgun wedding :eek: i hope not.
  2. jcsd
  3. Jan 23, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The 1.4 boy/girl relationship (if correct) is certainly not the natural ratio, which is very close to 1. I guess it is due to the 1-child policy in China, together with a traditional "lower value" of females, which makes couples abort until they have a boy - if that's the only child they're allowed to have.
  4. Jan 23, 2007 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Where did you read this? It sounds a little high. The sex ratio among the population was 1.12 a few years ago[1]. It's astounding that in that list of nearly 200 countries, there is not a single one with a male/female ration < 1. Or, there's just some simple genetic (rather than social) reason for it, that my biologically challenged mind is unaware of.

    But if the birth ratio is unusially high in China, it's predominantly due to the reason pointed out by vanesch.

    [1] https://www.cia.gov/cia/publications/factbook/fields/2018.html
    Last edited by a moderator: Apr 22, 2017
  5. Jan 23, 2007 #4
    I believe the US the number of children is around 2.2 which explains why it's population is increasing as around 2 is considered the cut off point, for rather obvious reasons. Many countries in Europe are decresasing bringing all sorts of doom and gloom prophecies, what they don't seem to realise though is that even humans are affected by environmental factors such as population density etc. UK's is pretty much static at around 2. used to be 2.4. Of course in Iraq the population is decreasing but this is mainly due to many people fleeing what is pretty much a war zone. 200 people died yesterday in car bombings etc. by 2 I mean children of either sex. Single sex will obviously decrease population.
    Last edited: Jan 23, 2007
  6. Jan 23, 2007 #5
  7. Jan 23, 2007 #6
    Are you talking about "replacement level fertility"? 2 births per woman is obvioiusly the correct figure. However, for some reason, girls that die before reaching child-bearing age are typically taken out of the equation so that the often cited figure is 2.1 births per woman. This figure, if maintained over a few generations, would result in a steady population. It also assumes that there will be about the same number of girls and boys born. However, the 2.1 figure is obviously not a precise one and so all assumptions are taken to be "rough".
    This site indicates that the figure for the US is 2.03
    In spite of the deficiency (2.03 rather than 2.1), population increases in the US for a variety of reasons. For one thing, the 2.03 figure has not been in effect for the length of time necessary for a steady state. Also, we have a significant influx of immigrants. In countries where children are more likely to reach childbearing age, the 2.1 figure may be a little high. I think the US probably can get away with a smaller figure than the world average.
  8. Jan 23, 2007 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I was recently reading a book on evolutionary biology where they said the same. Actually, I think that's wrong: it is not 2 births per female that is the correct figure, but 1 female per female. That is, consider the group of females. This can be the group of "newborn females", or the group of "adult and reproducing" females, it doesn't matter.

    What is needed, is that the average over said group, of all members, of their progeniture, is exactly 1 female "of the same kind". This means, that if we pick the group of "newborn females", then averaged over all newborn females, there should be 1 single descendent newborn female. Of course some of these don't procreate, but then, this is included in the average.
    Also, if we picked as a group "adult, procreating females", then, averaged over this SMALLER group, we should also have that on average an "adult procreating female" has exactly one descendent which is an adult, procreating female.

    Now, if the natural sex ratio is 2, then this means that in order to have this average of 1 descendent female, a female should have 2 descendants, of which 1 will be female on average. However, imagine a species that produces 10 times more males than females, but of which only 1/100 of the males will reach adulthood.
    When looking at "newborns", this means that a (newborn) female should have on average 11 newborn descendants. When looking at adults, it means that a n (adult) female should have on average 1.1 adult descendants.

    But what counts, in the end, is that the population of females remains constant, so each female should reproduce exactly one of its kind.
  9. Jan 23, 2007 #8
    The assumption of an equal number of girls and boys as well as the "rough" nature of the figures was mentioned in my post.
  10. Jan 23, 2007 #9

    Yes but more girls means less children in certain communities as a whole, since you need a girl and a boy to make another girl/boy. Thus this will reduce population; not a bad thing even if the means is of course questionable.

    I seem to have got my numbers wrong but the basic idea is sound.
  11. Jan 23, 2007 #10
    I assume that in communities where there is a supersufficiency of women of childbearing age, there is a tendency toward polygamy. You need one girl and one boy to make one child, but you only need one boy and two girls to make two.
  12. Jan 23, 2007 #11


    User Avatar

    Staff: Mentor

    This is all very interesting, but I'm a bit slow today - could someone please explain to me what exactly this has to do with the Iraq war?
  13. Jan 24, 2007 #12
    i know it's comming from left field but when you have too many young people and not enough land, jobs and women the older generation might wanna maintain the status quo and kill off those who will be the most likely to revolt.

    dangerous idea maybe but still worth pondering.
    Last edited: Jan 24, 2007
  14. Jan 24, 2007 #13

    I meant boys obviously. My bad again.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook