Icelandic women born between 1800 and 1824 who mated with a third cousin had more children and grandchildren (4.04 and 9.17, respectively) than women who mated with someone no closer than an eighth cousin (3.34 and 7.31). Those proportions held up a century later, when family size shrunk. Mating with a relative might reduce a woman's chance of having a miscarriage caused by an immunological incompatibility with her child. There is a limit to family closeness, however: couples that were second cousins or more closely related did not have as many children, probably because the kids inherited mutations that cut their lives short. —Nikhil Swaminathan


New languages spin off from older ones with an initial burst of alterations to vocabulary before settling down and gradually changing over time, British researchers report. The group focused on three major language families: Bantu (Swahili and Zulu, for example), Indo-European (English, Latin), and Austronesian (Tagalog, Seediq). Some 10 to 33 percent of divergence between languages stemmed from key vocabulary changes at the time of language splitting.

This discrete evolutionary pattern occurs when a social group tries to forge a separate identity, the researchers say, citing as examples the sudden emergence of American English when Noah Webster published his dictionary in 1828 and, more recently, the development of black American English. —Nikhil Swaminathan


Americans are losing interest in going outdoors. Researchers analyzed trends in visits to parks and forests and in licenses for activities such as hunting and fishing. All peaked between 1981 and 1991 after 50 years of steady increase. But since then, they have been declining at roughly 1 percent each year, an overall drop of as much as 25 percent. Electronic diversions may be taking over; increasing school and work pressure and “stranger danger” fear absent in previous generations may also be contributing. —David Biello