Wolfgang:
I do not have an article - but an older text (_Heredity, Evolution and
Society_, I. Michael Lerner and William J. Libby, 1976, Freeman Press) has a
brief discussion, and data it says comes from A.S. Parkes. Unfortunately, I
cannot find Parkes in their reference list. At any rate, Lerner distinguishs
(1) primary sex ratio (number of males conceived per 100 females conceived).
This ratio is much higher than 100, but difficult to determine with
precision, (2) secondary sex ratio, which is 106 (based on Parkes data), and
(3) tertiary sex ratio, which is after birth - and varies with age. The data
they have is:
age ratio (males per hundred females)
__ ___
18 yrs 100
50 yrs 95
57 yrs 90
67 yrs 70
87 yrs 50
100+ yrs 21
Thus, there are more males conceived, but higher mortality, throughout the
lifespan, with an equal # of each sex at 18 years. Lerner discusses some
interesting predictor variables for the ratios. The ratio is higher for
first borns than later borns, lower for poorer people, and (curiously)
higher after a major war. This last fact, according to some, illustrates how
"nature" compensates for the loss of men in war - thought this is nonsense
because there is no know mechanism for this to happen.
There are several proposed reasons for more males: (1) more Y sperm are
produced (2) more Y sperm reach eggs (3) Y sperm are more likely to induce
fertilization - all 3 have supportng data frm animal models. As to why men
are more vulnerable throughout life - (1) the y chromosome - lacking
genetic material, permits deleterious recessions on the corresponding X to
manifest itself in the phenotype (2) the higher testosterone of males -
while necessary for the development of sex characteristics - compromises
males' immune system, (3) (a subset of the previous point) testosterone
causes more reckless behavior in males - hence more deaths - at least during
adolescence.
Sorry I can't locate the Parkes reference, but Lerner and Libby should be
easy to find.
Wolfgang Rolke wrote:
> Hi,
>
> I am looking for information (journal article, web site ect.) on the
> difference in birth rates for boys and girls. Specifically I would like
> to find some real data and possible explanations for this phenomena. It
> seems to me that this would make a great example for an introductory
> stats course.
--
---------------------------------------------------------------
John W. Kulig [EMAIL PROTECTED]
Department of Psychology http://oz.plymouth.edu
Plymouth State College tel: (603) 535-2468
Plymouth NH USA 03264 fax: (603) 535-2412
---------------------------------------------------------------
"The only rational way of educating is to be an example - if
one can't help it, a warning example." A. Einstein, 1934.
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