A few days ago I mentioned that the story about a bumper crop of twins in a German town in southern Brazil was notable because of the elevated frequency of identical, not fraternal, twins. A reader points out that that was an error, and The New York Times has appended a correction:
The Cândido Godói Journal article on Monday, about the unexplained proliferation of twins born in the farming town of Cândido Godói in southern Brazil, misstated the type of twins usually associated with a genetic tendency of the mother. They are fraternal twins — like a majority of those born in the town. They are not identical twins, which are generally believed to be conceived by chance.
As I noted before, variation between populations and due to environmental inputs that affect twinning rates affect the rate of fraternal, not identical, twins. Inbreeding* or some environmental parameter, or a combination, probably explain this then.
* Since twinning is somewhat heritable, the alleles which modulate twinning rates could have increased in frequency in an inbred population through drift.