"Now, nearly 150 years later, a new generation of biologists is reviving Darwin’s neglected brainchild."

"Beauty, they say, does not have to be a proxy for health or advantageous genes. Sometimes beauty is the glorious but meaningless flowering of arbitrary preference. Animals simply find certain features — a blush of red, a feathered flourish — to be appealing. And that innate sense of beauty itself can become an engine of evolution, pushing animals toward aesthetic extremes. In other cases, certain environmental or physiological constraints steer an animal toward an aesthetic preference that has nothing to do with survival whatsoever... Darwin was contemplating how animals perceived one another’s beauty as early as his 30s: 'How does Hen determine which most beautiful cock, which best singer?' he scribbled in a note to himself sometime between 1838 and 1840.... Sometimes, males competing fiercely for females would enter a sort of evolutionary arms race, developing ever greater weapons — tusks, horns, antlers — as the best-endowed males of each successive generation reproduced at the expense of their weaker peers. In parallel, among species whose females choose the most attractive males based on their subjective tastes, males would evolve outlandish sexual ornaments."

From "How Beauty Is Making Scientists Rethink Evolution/The extravagant splendor of the animal kingdom can’t be explained by natural selection alone — so how did it come to be?" (NYT Magazine)(with many beautiful photographs of birds).