Final answer:
The elaborate plumage in male birds of paradise is due to sexual selection, specifically intersexual selection, where females prefer males with impressive traits. These traits may not be advantageous for survival but provide a reproductive advantage, leading to the prevalence of such traits in the population.
Step-by-step explanation:
The phenomenon you're describing, where male birds of paradise have evolved increasingly elaborate plumage because females preferentially mate with males displaying the most impressive feathers, is an example of sexual selection. This form of natural selection occurs when traits that increase an individual's chances of mating and reproducing become more common in a population over time, even if they do not necessarily improve survival. In the context of birds of paradise, the bright plumage of males does not enhance their survival and may even pose a detraction by making them more visible to predators. However, because these traits are attractive to females, they confer a reproductive advantage to the males that possess them, leading to the prevalence of these traits in subsequent generations.
Intersexual selection is a component of sexual selection where females choose a mate based on certain desirable characteristics, such as bright plumage. This can be contrasted with intrasexual selection, which involves competition between members of the same sex, often males, as they vie for mates. Both types of selection can lead to pronounced differences in appearance and behavior between males and females, known as sexual dimorphism.
An example of intersexual selection includes female peacocks being attracted to males with the brightest plumage. The 'handicap principle' might explain this preference, suggesting that males with such extravagant traits have better genes and, therefore, despite the survival risk, are more desirable mates.