Tim writes:

>> Male excess mortality in some mammals appears to be directly and
>> programmatically derived from androgenic hormonal levels, especially
>> testosterone. Castrated human males live on average 13.6 years longer
>> than unmodified men. [...]
>
>...according to one old study on mental patients.
>
>More recent work has failed to detect any such effect:
>
>``Androgens shorten the longevity of women: sopranos last longer''
>
>  Earlier we found that longevity of castrati was identical to that of 
>  intact singers. These findings were in disagreement with the prevailing 
>  concept that testosterone might shorten life and might be responsible 
>  for the shorter life expectancy of men compared to women. [...]''
>
> - http://calorierestriction.org/pmid/?n=12845562

The effect that's generally reported isn't presumed to have much to do with the
biochemistry of testosterone, as the above report suggests. Rather the effect
on shortened lives of males is thought to be much more a consequence of the
aggressive behaviors that it promotes. Castrated males tend to be much more
passive individuals and much less likely to engage in risky combative behaviors
than either normal males or females.

In humans, male-male combat begins at puberty and lasts throughout the
reproductive age. You can see that behavior in the chart below, which catalogs
excess male mortality relative to human females in two groups, those in Chicago
and England/Wales. The two curves are astoundingly similar, but with the small
caveat that the male-male murder rate in Chicago is 30 times higher than it is
in England:

     http://aics-research.com/maleexcessmortality.html

The ready availability of guns in the US is generally credited for the
difference in murder rates.

Nonetheless, such aggressive behavior in humans is merely only a shadow of the
intensity of the conflict that exists a great many other large mammals. I
reported earlier that adult Soay ewes outnumber rams by 5:1 after their first
breeding season. Most of that excess male mortality is winter mortality that
occurs because of the weakened condition that the males find themselves in
after the rut.

While such much reduced male frequencies are common in adult ovids, equiids and
cervids, it's in the pinnipeds that the operational sex ratio becomes truly
maximally skewed. This disproportionate loss of males from the population is
credited almost solely to the single-mindedness of the males in their efforts
to engage in combat and to own a harem. 

There was an extraordinary photograph of fur seals on the South Georgia Islands
in National Geographic a few years ago graphically illustrating this effect.
I've put it up on our webpages:

     http://aics-research.com/southgeorgiaseals.html

The caption to the photograph reads:

"Jumbled scene of life and death in a fur seal colony confronts member of the
BAS team as they escort the Poncet children from the Damien II after it docked
at Bird Island. Long sticks called bodgers are kept handy to fend off attacks
by aggressive bull seals. Amid the smaller cows and pups, the bulls rise up on
their front flippers as they proclaim dominance over their territories. Already
weakened by fasting during the mating season, some have succumbed to injuries
suffered in fighting over the cows. Skuas and giant petrels are quick to reduce
the carcasses to mere bones." 

Wirt Atmar
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