Survival of the fittest. This is perhaps the most iconic lesson taught by Darwin.
Most evolutionary theory is based around the concept of fitness. When applied to natural selection, it implies that a species will evolve to sustain traits which are better adapted, and more likely to thrive in a given environment. It's the prototypical idea that living things select mates based on the physical attributes which give them the best chance to survive. Over generations, a species is left only with those traits.
But a lesser known fact is that Darwin himself was conflicted about whether or not fitness was the only factor in sexual selection. Could preference also play a role in mate selection? Looking at the way humans choose mates, one could certainly come to that conclusion, although that is also debated. But the idea that other spices in the animal kingdom could choose mates based on preference was never more than a fringe idea.
The most recent episode of Radiolab, The Beauty Puzzle, explores this fascinating topic.
A species of birds in New Guinea called the Bowerbird exhibits mating behavior which would indicate that preference may play a role in mate selection. Male bowerbirds spend most of their lives learning how to build the elaborate gate-like structures out of twigs, fruits and other objects in an attempt to impress potential mates. They take enormous care to decorate their bowers to be aesthetically pleasing, even paying attention to things like color arrangement and plucking out loose ends.
Females inspect the bowers as males look on waiting for their approval. They are constructed in such a way that the female is never at risk of an ambush by the male – she can flee at any point.
According to at least one scientist and ornithologist Richard Prum (and author of the book The Evolution of Beauty), this is evidence that there is more to mate selection than fitness. Animals, like humans, are able to express aesthetics preference.
There is a segment on bowerbirds in the Birds episode of the excellent BBC nature documentary Life. It's available on Netflix.
- Survival of the Prettiest, New York Times
- Challenging Mainstream Thought About Beauty’s Big Hand in Evolution, New York Times