What Is Bateman’s Principle?

At its core, Bateman’s principle states that reproductive variance is greater in males than in females. In other words, the number of offspring produced by males can vary much more widely than the number produced by females within a species. This difference is rooted in basic biological and evolutionary factors:

• Gamete Investment: Females typically produce fewer, larger, and more energetically costly eggs, while males produce many small, inexpensive sperm.

• Limiting Factors: A female’s reproductive success is limited by her ability to produce eggs, whereas a male’s reproductive success is limited by access to females.

• Sexual Selection: Because males can potentially father many offspring by mating with multiple females, there is more intense competition among males for mating opportunities.

Key Predictions and Observations

Bateman’s principle leads to several important predictions about animal behavior and evolution:

• Greater Reproductive Variance in Males: Males show higher variance in reproductive success than females—some males may father many offspring, while others may have none.

• Sexual Selection Pressure: Stronger sexual selection acts on males, leading to the evolution of traits such as elaborate displays, weaponry, or aggressive behaviors.

• Female Choosiness: Females, being the limiting sex, are generally more selective in choosing mates, while males compete for access to females.

Why Not the Other Statements?

• Costlier Female Gametes: While Bateman did note that eggs are costlier than sperm, this is a foundational observation, not the principle itself.

• Parental Care and Male Displays: These are consequences of sexual selection and parental investment theory, but they are not the central tenet of Bateman’s principle.

Conclusion

The statement that best describes Bateman’s principle is:

Reproductive variance is greater in males than in females.