Female fish evolve bigger brains to escape males with bigger genitals forcing them to mate: study
Eastern Mosquitofish (aquariumlife.net)

Despite what you might think, evolution rarely happens because something is good for a species. Instead, natural selection favours genetic variants that are good for the individuals that possess them. This leads to a much more complicated and messy world, with different selective forces pushing in many directions, even within a single species. One prominent consequence…