What does uric acid do?
While high levels of uric acid are abnormal in human urine (we use urea, a water-soluble compound, to get rid of our nitrogenous waste), there are plenty of animals that use water-insoluble uric acid as their main nitrogenous waste, and it’s not just because they’re “lower” animals (man, I hate that term). The evolutionary reason is basically water conservation. If you’re looking to conserve water, as many land animals (some insects, birds, reptiles, and even some mammals) are, one great way to do it is by reducing the amount of water you require to flush out your nitrogenous waste. uric acid does this nicely, because it turns into a sort of pasty white goop which requires a LOT less water to flush out of an animal’s system than an equal amount of urea. In bird poop (which is actually poop AND pee), the white stuff is the uric acid, while the chunky brown stuff is the actual poop.
