Let's face it: Valentine's Day is stressful. Maybe you've been making eyes at a guy or gal, and it seems like the time is right for some grand gesture. Or maybe you did the hard part and found someone great, and you don't want to disappoint. We can look at books or art or history for inspiration; at Lloyd Dobler in Say Anything; or, at Nebuchadnezzar II, who built the Hanging Gardens of Babylon to "ease the homesickness of his wife Amytis." But love and life are primal things, and for some inspiration, some proof that you're not doing it wrong—or that you are—there is no better place to look than in the animal kingdom around us.
It all begins with sexual selection. Darwin broke the science of selection into two main categories: intersexual and intrasexual. In the former (also called "mate choice" or, depending on the species, "female choice") males compete for the attention of females, the ultimate arbiters. In the latter, members of one sex (generally males) compete directly for access to the other sex—this is where you get epic battles like those between elephant seals:
Male elephant seals do all their fighting over territory, before the females are even around. By the time the females get to the rookery, the beach is already divided. Intrasexual selection can also help to explain the development of antlers and, surprisingly, the long neck of the otherwise elegant giraffe, which can be used for some very vicious street fighting.