Birds of paradise are a unique paradigm of the evolution of extraordinary traits through natural and sexual selection. These traits involve colorful plumage, sophisticated ornaments and elaborate dances that cannot only be attributed to having a positive effect on the bird’s survival, but mostly on increasing the chances for it to breed and pass its genes to the next generation.
Regarding common ancestry, this is an excellent example of speciation, that is how new species emerge from ancestral ones. There is genetic evidence that all 39 species of birds of paradise in New Guinea and surrounding islands originate from a common ancestor, a plain crow-like bird with average appearance. Populations of this ancestral species became geographically isolated from one another due to dramatic geological events that took place in New Guinea and surrounding islands. These changes split original habitats, fragmenting the original population that lived there. After millions of years of isolation, the individuals accumulated genetic differences and the inability of interbreeding. The former together with natural and sexual selection led to new species.
Biological evolution is also supported both in terms of natural and sexual selection. Natural selection has enabled the isolated populations to survive by promoting those individuals that were able to exploit new nutritional resources more efficiently, when they first arrived at their new habitats.
In an average population of newcomers mutations occur randomly. Some of them are negative, others positive and some neutral. Imagine a positive mutation (one that has adaptive value) that changes the shape of the beak (let’s say its length) so as to enable that specific individual to exploit a nutritious and plentiful resource on the island that no one else can. This trait is encoded by genes and is passed to the next generation because this bird is better adapted to its environment and is more competent to survive, gather resources and reproduce. As time passes, this new trait spreads in the population and after a number of generations most of the birds possess this characteristic.
Now that there is no need to worry about nutritional resources, the females assume the responsibility of caring for their young, allowing males to have time and energy to compete for the females. Gradually, sexual selection takes over the reins, diversifying males and females of the same species to such an extent that males are considered extremely beautiful in appearance and females comparatively dull. Dull, but not unimportant because it is the females’ choices that shape the course of evolution. The males have their fancy appearance to attract females. The females by closely examining ornamentation and showing-off in males, determine which one is the healthiest or simply the most beautiful (they also have aesthetical preferences in mating) to mate with. The interesting part is that the genes that control the fancy traits in males go hand in hand with the female preferences for males with fancy traits and thus result in diversity. Natural selection is still active in females because it favors their dull camouflage coloration.
The unique and complex behaviors (elaborate dances, courtship display) that male birds of paradise exhibit are very good examples of adaptations determined both by genetic and environmental factors. Part of these behaviors is inherited by their parents and part is the result of practice (alone, with other males, watching other males practice, watching other males dancing and displaying courtship behavior).
The close study of Birds of paradise in their extreme variety of appearance and fancy behaviors can be a helpful tool in supporting natural and sexual selection, speciation and common ancestry. This example equally competes with Darwin’s studies on Galapagos finches in empirically supporting biological evolution.
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