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muriel_volestrangler

(106,226 posts)

8. Primary sex ratio up to 170 males to 100 females

Reply to cthulu2016 (Reply #2)

Sat Feb 18, 2012, 02:03 PM

Feb 2012

The primary sex ratio (male:female ratio at the time of fertilization) in humans differs remarkably from the theoretically expected ratio of 1:1, and may be as high as 170 males to 100 females (Pergament et al., 2002). Because the secondary sex ratio (or ratio at birth) is ∼106:100 in the majority of developed countries, it is clear that preimplantation and prenatal mortality affects sexes differently.

http://humrep.oxfordjournals.org/content/20/9/2662.full

(On edit: added 'up to')

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Why are males and females 50%-50%? [View all] cthulu2016 Feb 2012 OP

Silly me, I learned the natural ratio at birth was 107 boys to 100 girls Brother Buzz Feb 2012 #1

That's birth, not conception. cthulu2016 Feb 2012 #2

Primary sex ratio up to 170 males to 100 females muriel_volestrangler Feb 2012 #8

Fair enough cthulu2016 Feb 2012 #12

I've read that there are more males than females are born in the U.S. Honeycombe8 Feb 2012 #19

I ammended the OP to reflect cthulu2016 Feb 2012 #23

Also, boys traditionally had a higher mortality rate. Arugula Latte Feb 2012 #7

Speak for yourself karynnj Feb 2012 #3

The ratio of boys to girls at birth ranges from 1.03 to 1.07 generally, depending on country FarCenter Feb 2012 #4

Sex ratio is a feature of a species natural history traits HereSince1628 Feb 2012 #5

Maybe it maximizes the experiment potential. gulliver Feb 2012 #6

Assume there is such a thing as truly random, then random coin flips are 50% heads 50% tails. retread Feb 2012 #9

By population, women in the US make up about 52%, partially by attrition. HopeHoops Feb 2012 #10

I think the ratio is about bottlenecks napoleon_in_rags Feb 2012 #11

That's attractive but cannot be right cthulu2016 Feb 2012 #13

Hmm, interesting. napoleon_in_rags Feb 2012 #15

No here is the answer, Fisher's principle. napoleon_in_rags Feb 2012 #17

Exactly (I was trying to say that in the OP but may have failed) cthulu2016 Feb 2012 #18

It's probably more complex than that, particularly in species which are polygynous and bear litters FarCenter Feb 2012 #20

Very true cthulu2016 Feb 2012 #24

Yeah, you're right... Here's a good article: napoleon_in_rags Feb 2012 #30

Again, note the "afford to gamble" factor cthulu2016 Feb 2012 #34

Yes indeed. Do you ever see this stuff holistically cthulu? napoleon_in_rags Feb 2012 #37

Me to. My approach to posting is atypical cthulu2016 Feb 2012 #39

You bring tough questions to the surface. napoleon_in_rags Feb 2012 #40

well said. n/t lumberjack_jeff Feb 2012 #28

It is not a gene quaker bill Feb 2012 #31

That process is not as random as it would seem though. napoleon_in_rags Feb 2012 #38

Unless you are a mouse, no you can't. quaker bill Feb 2012 #42

It seems unlikely to me that a bottle-neck would lead to a change in species mating-systems HereSince1628 Feb 2012 #22

Nicely written. cthulu2016 Feb 2012 #25

My theory is that it only became important to have sons when we became Cleita Feb 2012 #14

Here's a question. Igel Feb 2012 #16

For most species, the sex ratio is approximately 1:1 cthulu2016 Feb 2012 #21

This from an earlier post of mine TexasProgresive Feb 2012 #26

How a sperm cell is formed has to do with it. 2ndAmForComputers Feb 2012 #27

True, but that is not the mechanism cthulu2016 Feb 2012 #33

Mitochondrial DNA Another Bill C. Feb 2012 #29

Wikipedia has a sortable chart on gender ratio: more guys at birth, more gals after 65 yurbud Feb 2012 #32

And with the 1:1 crossover ocurring cthulu2016 Feb 2012 #35

I just realized this balances out a biological injustice: yurbud Feb 2012 #36

I have a question.... unkachuck Feb 2012 #41

Except now in some places... like India and China JCMach1 Feb 2012 #43