Tom,
Hopefully I can do a better job at explaining this today (I wrote
the last post very tired at almost 1am)
I believe that the findings of these two sets of studies shows us
there is some sort of sex selection happening, not based on chance, but
based on what is beneficial for the offspring's longevity (living longer
should give a newborn a better chance at reproduction and rearing children
of their own).
The study from Nature tells us we can expect a couple's firstborn
children to be of the opposite sex of the oldest parent (statisically at
least). What it doesn't tell us is whether the odds get better when the
age difference of the couples is greater than 5 years. In my own case,
my father was 18 years older than my mother, and I am the first born (N=1
of course).
Currently the work of Gavrilov L.A. (1997,1996) shows that the
daughters of older fathers live a shorter period of time than those born
of younger fathers.
I do not know if any studies were done with sons born from older
mothers have a slightly shortened life expectancy, but it wouldn't suprise
me: Down's Syndrome is a predominately male disease, and the risk factor
increases with the age of the mother. Of course, D.S. children show
signs of accelerated aging (Aging Sex and DNA repair (1991) goes into this
in detail). I do not know the statistics of other genetic syndromes,
and whether aborted fetuses are ever counted in these studies. For
instance, if every D.S. child were aborted (god forbid - my little brother
has D.S. and I love him to death) wouldn't this affect statistical studies
regarding sons born to older females and lifespan?
...To your original question: Why doesn't the older person in
the pair pass on their genetic mutations to their same sex offspring?
I have no answer for you. Maybe someone with more genetics
background can help me on this.....It seems the topic of a neat research
paper, but I'm in the wrong field for that. The older you are though
the more chance of *NOT* having a baby there is. Mother nature selects
sex based on what is better for the baby's reproductive success IMO.
This an interesting topic. I hope more research into sex
selection and longevity determination based on parental age will be
forthcoming soon.
...Rodney
Tom Matthews (tmatth at netcom.ca) wrote:
: Rodney Reid wrote:
: >
: > From the journal Nature this week comes a study that shows how
: > differences in the age of the parents influences the gender of their
: > firstborn.
: >
: > The study consisted of a group of 301 british families, in which
: > the researchers found if men married women at least five years younger
: > then them, the chance of them having a firstborn son instead of a
: > firstborn daughter is 2-1. The same is reversed for the older woman,
: > younger man scenario, with firstborn daughters occurring 2-1.
: > Maybe it's just me, but I see a correlation, and a reason
: > (method?) as to why the two are related: the older parent can possibly
: > pass on age related mutations to their offspring of the opposite sex,
: > which is why it's (statistically) decided against.
: I agree that its very interesting, Rodney, but I don't understand the
: logic of your correlation.
: But why don't they pass these same mutations to their same sex
: offspring?
: I believe I have read that the sperm of older men produce less viable
: embryos.
: --Tom
: Tom Matthews
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