Another example of the influence of in-utero development is what’s called “androgenization.” In this phenomenon, females in a litter are permanently affected by the androgen produced by male puppies surrounding them within the uterine horns. Androgen is the precursor to testosterone, and females who are “bathed” in it, perhaps because of their placement between a large number of males, tend to behave differently than other females once they develop into adults. Androgenized females behave more like males, sometimes have enlarged gentalia and are often more aggressive to same-sex individuals.
And so, even prior to birth, profoundly different experiences could have shaped Holly and Kit. The combination of different genetic blueprints and different experiences inside the womb resulted in two dogs with very different personalities and tolerances. Even though they have grown up together, those beginnings mean that a similar environment will affect them in different ways as they continue to develop. Holly will probably always be more cautious than Kit, because much of who she is was established before she was born. This is not to say that shy little Holly can’t become more comfortable at the dog park—or with runaway purses—but it does remind us how and why every dog is a unique creation and special in her own way. And special they are, every one of them.
Patricia McConnell, PhD, is an animal behaviorist and ethologist and an adjunct associate professor in zoology at the University of Wisconsin, Madison, as well as the author of numerous books on behavior and training.