Big boss cat in Japan. I am sure he has the smelliest pee. He looks unneutered (jowly). Photo by David Panevin.

Female cats are choosy when they select a tomcat to be the father of her kittens. It’s the same with female humans. Tomcats therefore need to advertise their suitability to the females. They probably do this through their pungent urine, which they spray horizontally on prominent objects in their territory. Which tomcat comes out on top and gets the girl? The one with the smelliest urine.

This is because a tomcat with the smelliest urine is the best fed cat amongst males. In turn this is because he is able to survive better than most, an essential and attractive quality for a female cat as she wants her offspring to survive more capably (this is my observation).

The reason why a tomcat who eats well has pungent urine requires a trip to the chemistry classroom. A chemical called ‘felinine’ is generated in the cat’s bladder by a protein called ‘cauxin’.

Felinine is made of two amino acids: cysteine and methionine. They both contain the sulphur atom which is what gives the urine it pungent odour.

Cats can neither make cysteine nor methionine for themselves. The amount of felinine they have is dictated by the amount of high protein in their diet. This is determined by how good a hunter he is. Thus the tomcat with the most pungent urine is the best hunter and best able to survive and provide. He is the most capable. He gets the girl.

At present, scientists don’t know how a female matches the urine with the male who deposited it. It is believed that there is some signal in the urine other than the pungent sulphur compounds that gives the female the information to recognise the male who has the smelliest pee.