Ending Pregnancies

Mothers' protective instincts toward their young is one component of animal psychology that we would suppose is innate. There are several instances of this in nature documentaries. There are numerous videos of this on YouTube that have amassed millions of views. After all, it stands to reason that any species whose ability to reproduce isn't given top priority will probably become extinct quite rapidly. But in some species, the females will fully override the initial reproductive instinct—not out of necessity or for any other reason, but only because a new male has appeared.

For instance, the geladas are an Ethiopian primate that live in groups led by an alpha male. It has been shown that the number of miscarriages among the community's females can increase by as much as forty times if another male murders that individual. Although this phenomena was initially noticed among gelatos in 2012, Dr. Hilda Bruce originally noticed it in mammals in 1959 while noticing a sharp spike in mouse abortions when she placed young male mice alongside pregnant females. The Bruce Effect is the name given to this naturally occurring increase in miscarriages, and it must rank among the less honorable names in biology.