Today we consider what biology can tell us about the human population. In October of 1999 the human population turned 6 billion . Until very recently, the growth of the human population has approximated a J-shaped curve.
Human fertility varies greatly on a regional basis.
One way population demographers compare populations is through calculation of the TFR, or total fertility rate , for a population. TFR is defined as the average number of children women in that population will bear in their lifetime . TFRs change, decade by decade, but most studies suggest that the TFR for the United States is around 2, probably a little higher. Thus, the United States falls in the middle grouping of TFRs, neither extremely high nor extremely low. Historical studies of changes in populations suggest that societies follow patterns predicted by stage of economic development.