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Previously, the researchers had classified marmots with long AG distances are males and shorter AG distances are females. Classification based just on AG distances first led to some confused researchers. Some of the long AG distance marmots, which researchers thought were males, seemed to undergo a sex change — they were actually females all along. Previous research has shown that these females with longer AG distances come from litters containing more males than females. And since the AG distance indicates testosterone exposure in the womb, the researchers figured the brother's testosterone had changed the female's AG distance; they wondered if it had any effect on the female marmots' behaviors, as well.

wandered farther and pursued more play-fighting with more play partners than the more feminine females.

Whether a litter is male- or female-biased is dictated by the environment.

Male animals traditionally need more investment from their mothers, because they are larger. In some conditions, like when the environment is steady and resources are plenty, it might make sense to invest more in males. "For instance,  when mothers are in good conditions they usually have male-biased litters, whereas in bad body condition they have female-biased litters."

If hormones like testosterone from littermates are impacting marmots' behavior and reproduction, chemical pollutants that have similar structures could screw up these signals.

These pollutants, also known as endocrine disruptors, could interfere with the mothers' intended "decision" to have a female- or male-biased litter.