Final answer:
Male and female reproductive fitness can be affected by factors like sperm availability, female fecundity, and energy budgets for males, as well as societal influences on female fertility such as education, economic opportunities, and family planning.
Step-by-step explanation:
From a reproductive standpoint, the fitness of males and females can be limited by several factors. In studies from 2006, it was shown that male reproductive success is influenced by previous matings, with sperm-depleted males showing a preference for larger, more fecund females. These larger females have greater fecundity, producing more offspring, and thus represent a better opportunity for males with limited sperm to pass on their genes. Such behaviors are an example of how animals manage their energy budget in reproduction to ensure the best chance to pass on their genes—important research in the field of behavioral biology or ethology.
Furthermore, factors such as energy availability, educational and economic opportunities, gender equality, knowledge of family planning, and access to contraception can influence female reproductive success and fertility rates at a societal level. Within sexual selection, there's the concept of the good genes hypothesis, suggesting that females select males with superior traits, resulting in healthier albeit fewer offspring, which can be more beneficial in the long term.