The lowly seer

Urine

A little more from James Lovelock's "Revenge of Gaia" - why do we urinate?

The need to rid oneself of waste products like excess salt, urea, creatinine and numerous other scraps of metabolism is obvious but only part of the answer....
For us, the excretion of urea represents a signicant waste of energy and water.

Urea is a simple chemical, a combination of ammonia and carbon dioxide, or as an organic chemist would say, the di-amide of carbonic acid. Why did we and other mammals evolve to excrete our nitrogen in this form? Why not break down the urea into carbon dioxide, water and nitrogen gas?Much easier to excrete the nitrogen by breathing it out, and it would save the water needed for excreting urea; oxidizing the urea would even add a little water, to sy nothing of providing more energy.

Let us look at the figures. 1000 grams of urea is metabolically worth 90 kilocalories. But if intead of being consumed it is passed in urine, more than 4 litres of water are needed to excrete the 100 grams of urea at a non-toxic dilution. Normally we excrete about 40 grams of urea daily in about 1.5 litres of water....
So you see, urea is waste for us and wasting it loses valuable water and energy. But if we and other animals did not pee and breathed out nitrogen instead, ther might be fewer plants and later we would be hungry.

The nitrogen in urea can be used by the bacteria that symbiotically coexist with the roots of plants and passed through to the plants themselves. Fertilizer, in other words. (Next time someone catches you pissing their flower bed on your way back home from the pub, you can quote this blog to them).

Urination, to an individual, is as such not a great way of doing things. Birds excrete solid(ish) uric acid instead, as to use water in this way would increase their weight greatly, making it more difficult to fly. It's also used to remove temporary imbalances of useful substances (which is how come some people reckon drinking their own piss is good for them); obviously it'd be better if they could be stored and re-used somehow.

The big problem here is that with the reductionist view of evolution, animals that could break down urea as suggested above would be superior and flourish over the urinators, but when you move away from viewing the fauna as individuals and look at the system as a whole, one with urinators will produce more and healthier plants which in turn will support more animals.

posted by Les the Spaceman @ 1:32 pm