Twinning rates and seasonal changes in Görlitz, Germany, from 1611 to 1860.

Old-age twinning rates were evaluated over a period of 250 years (1611-1860), from 80,256 parish records of baptism in a church office in Görlitz, East Germany. Two periods with high and two periods with low twinning rates were observed. Twinning rates were relatively stable in spring and fall, but varied greatly in winter and summer.