The theory of evolution explains the diversity of life on Earth through mechanisms such as natural selection and genetic drift. An interesting aspect of this theory is its application to behavioral traits in organisms. Behavioral adaptations can significantly affect an organism's fitness in its environment. One popular example of behavioral evolution is the mating strategies observed in certain species. Populations can exhibit different mating systems based on various environmental and social factors. Consider a population of birds where some exhibit monogamous pair-bonding while others are polyandrous. Which of the following statements best explains how these different mating strategies might evolve?