from memory the reproduction rate has to be 2.144/per parental unit for pop stasis-and usa births declined to 2.144 children/parental unit in 1972 just before abortion became legal in the usa
why 2.144 instead of 2- dont know absent infant mortality--but 2/3 of new agers might say it was due to those ever present pesky alien abductions (humor for the rest of us)


http://r.search.yahoo.com/_ylt=AwrTccULxulVPN...M_z3m9NDc-