Glenn Weisfeld, a human ethologist at Wayne State University, takes issue with the findings of a Pennsylvania State University research team. The study concluded that the pheromones (scent) a young girl's father gives off not only prevents inbreeding, but also stalls menarche (when a girl first has her period). Weisfeld said that the authors do not conclusively demonstrate that these changes in timing of menarche are due specifically to pheromones. "Merely showing a statistical relationship between father absence and age of first menstruation is not enough," Weisfeld said.