What Is Sexual Selection?

Sexual selection is a type of natural selection that arises from differences in mating success among individuals. While natural selection favors traits that enhance survival, sexual selection favors traits that improve an individual’s chances of attracting mates and reproducing. This can lead to the evolution of features that are advantageous for mating, even if they come with survival costs.

How Does Sexual Selection Lead to Male Ornamentation?

Sexual selection operates through two main mechanisms:

• Female Choice: Females often prefer to mate with males that possess certain traits, such as vibrant colors, long tails, or complex songs. Over generations, males with these preferred traits are more likely to reproduce, passing their genes—and their ornaments—on to the next generation. This process is known as intersexual selection.

• Male-Male Competition: Males may also evolve ornaments or weapons to compete with other males for access to females. The most impressive or dominant males win the right to mate, further propagating their traits.

Examples of Sexual Selection in Action

• Peafowl: The peacock’s tail is a classic example. Although the tail is cumbersome and makes the bird more vulnerable to predators, peahens consistently choose males with the largest and most symmetrical tails. This preference drives the evolution of even larger and more elaborate tails over time.

• Birds of Paradise: Males perform intricate dances and display vivid plumage to attract females, with the most impressive displays winning the most mates.

• Stalk-Eyed Flies: Males with longer eyestalks are more attractive to females, leading to the evolution of exaggerated eye structures.

Why Not Directional, Co-evolution, or Natural Selection?

• Directional Selection: While this form of selection favors one extreme of a trait, it is not specific to mating success. Directional selection can play a role in sexual selection, but the key driver for ornamentation is mate choice, not just a shift in trait frequency.

• Co-evolution: This refers to reciprocal evolutionary changes between interacting species, such as predators and prey or hosts and parasites. It does not specifically explain the evolution of male ornaments.

• Natural Selection: This broader concept includes all selection for survival and reproduction, but the specific driver for male ornamentation is sexual selection, which can sometimes act in opposition to survival-based natural selection.

The Science Behind Male Ornaments

Research shows that elaborate male ornaments serve as honest signals of genetic quality, health, or vigor. Only the healthiest males can afford to produce and maintain such costly traits, so females use these ornaments as cues when selecting mates. This is known as the “handicap principle,” where the ornament is a sign of a male’s fitness because it is costly to produce and maintain.

Modern Insights and Ongoing Research

While sexual selection is the primary explanation for increased male ornamentation, scientists continue to explore other factors, such as social selection and ecological influences. However, the consensus remains that sexual selection—through female choice and male competition—is the main evolutionary force behind the development and exaggeration of male ornaments.

Conclusion

The increase in male ornamentation during evolution is best explained by sexual selection. Through mate choice and competition, males with the most impressive ornaments gain a reproductive advantage, ensuring that these traits become more pronounced in future generations. This dynamic interplay between attraction and reproduction shapes the dazzling diversity of ornaments seen across the animal kingdom.

Correct answer:
(3) Sexual selection