PHOTO CREDITS: Banner courtesy Oborseth/Wikimedia Commons; Crowd photo courtesy Ed Mutchnick; Polar bear courtesy Flickr/flickrfavorites; Martha, the last passenger pigeon — public domain (.); Coquí guajón courtesy Luis O. Nieves; Langes metalmark butterfly courtesy USFWS; Pacific walruses courtesy USFWS; Ribbon seal by Dr. Peter Boveng, NOAA; Sandplain gerardia courtesy USFWS; Orca courtesy NOAA; Florida panther courtesy USFWS; Pika courtesy Flickr/Lukas Vermeer; Forest Path courtesy Anja Jonsson/Flickr; MuleDeer courtesy Oborseth/WikimediaCommons; Horned Lizard courtesy Brad Smith/Flickr.
. fertility, or birth rates, first dropped to less than replacement level fertility in 1972. Yet . fertility is still dramatically higher than most all developed countries. For example, Europe's aggregate fertility varies between approximately and , depending upon region. According to the Census Bureau's decennial census, . population is growing by approximately million per year. The growth due to natural increase is million per year (total births minus deaths, including native-born births and births to immigrants).