Suitable definitions of "humans":
- people in the US
- people in industrialized nations

Suitable definitions of "reproduce"
- have children right now
- have had children at one point in their life
- are likely to have children based on some extrapolation

Note: children-per-woman statistics are all over the place, but not
acceptable.  The hardest part of answering this question is the fact
that most statistics-gatherers care about the *number* of children,
not the *number of people who have children*.  You can't compute one
from the other since the former gives greater weight to people with
lots of kids, and the latter does not.

Hello.

According to research cited by the American Association of University
Professors, 87% of women and 81% of men reproduce.

"Eighty-seven percent of women become parents during their working
lives. 3
...
3. Jane Waldfogel, "The Effect of Children on Women’s Wages," American
Sociological Review 62 (1997): 209.

Similarly, 81 percent of men become fathers at some point in their
lives. See Nancy E. Dowd, Redefining Fatherhood (New York: New York
University Press, 2000)"

source:
American Association of University Professors
http://www.aaup.org/statements/REPORTS/re01fam.htm


Similar percentages are reported by the US Department of Health &
Human Services

Percentage of adults ages 45 and older who have ever had a biological
child (2000)
Males: 84%
Females: 86%

source: 
US Department of Health & Human Services
"Charting Parenthood: A Statistical Portrait of Fathers and Mothers in
America"
http://fatherhood.hhs.gov/charting02/introduction.htm#Who

Of course, these percentages do not include the adults ages 45 and
older who have not yet had their first child but eventually do so.
However, against the population as a whole, such people aren't going
to be statistically significant.

The number of births to women 45 to 54 years old was 4,565 in 2000.
source: Associated Press
http://www.myrtlebeachonline.com/mld/sunnews/2642279.htm

4,565 births represents only a tiny percentage of the total births in
the U.S., and it is even less significant for purposes of this
question when you consider that many of those mothers were not
first-time mothers. And while men older than 45 can and do father
children, the percentage of men who become first-time fathers at 45 or
older is very small.

Also see:
ABC News
"Eighty percent of Americans today become parents."
http://abcnews.go.com/sections/living/Healthology/women_nochildren1020603.html

----------

Here are various related statistics from countries other than the
U.S.:


"Australia...
For women born more recently childlessness appears to be on the rise
and on current rates is expected to reach 28%."
Australian Demographic Statistics
Special Article - Lifetime Childlessness (Sep, 1999)
http://www.abs.gov.au/Ausstats/abs@.nsf/Lookup/1DECC52B47FC8E26CA2569DE002139C1

"Only 10 percent of French women will not have children, which is
indeed low, compared with countries like Germany, where it reaches 17
percent. "
source:
 info-france-usa.org
http://www.info-france-usa.org/publi/nff/0201/soc.htm


"Canadian research suggests that around 11 percent of men will not
have children."
source: Teendads.org.za
http://www.teendads.org.nz/fatherandchild/fcarchives/issue08/blended.html

--------------

search strategy:
percent "become parents" "some point"
"men will have children"
"women will have children"
"americans will have children"
percent "ever have children"
"birth to at least one child"


I hope this helps. If anything is unclear, please let me know via the
"request clarification" feature. Thanks.

Rock on!  Exactly what I wanted (and more).

Thank you for the tip.
-juggler