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Life sciences/Developmental biology/Reproductive biology/Human reproduction/Birth control

The world population may increase through 2100, and a new projection points to Sub-Saharan Africa as a primary engine for sustained global growth.

Researchers have pinpointed a genetic mutation that may help explain why some men are less fertile than normal, a new study in the 20 July issue of the journal Science Translational Medicine reports.

The gene encodes a protein called beta-defensin 126, which coats the surface of sperm and helps them penetrate cervical mucus in women. Men with a variant of this gene, called DEFB126, lack beta-defensin 126, making it much more difficult for sperm to swim through the mucus and join with an egg.