To get straight to the point the reason why domestic cats often have white socks is because during the early centuries of cat domestication people liked to see rare tabby cats with white fur on their paws so they made sure there were more. Today they are called tabby-and-white cats. They are not a breed but the term decribes a coat type.
At the beginning all domestic cats were tabby cats because their wild cat ancestor, the North African wildcat is essentially a tabby cat. So the domestic cat inherited their wild cousin’s coat.
Genetic mutations occurred as is normal in nature and some domestic cats had white paws. If these cats had been wild they would have died out through natural selection because white paws would have ruined their beautiful camouflage and they’d be easier to prey upon.
But as they were domestic cats living with people, natural selection, as invented Charles Darwin, did not take place. What replaced it was selective cat breeding i.e. artificial selection. Thousands of years ago the first tabby cats with white socks would have stood out from the crowd and been regarded as special and different. People were attracted to them and they made sure that they bred to produce offspring and that the kittens survived.
Gradually cats with white socks became commonplace. And gradually through more genetic mutations tabby coats become solid colours and tortoiseshell coats and so on. And these cats also had white paws sometimes.
The gene that causes them is the piebald or white spotting gene. It is the gene that produces the solid-and-white coats as well and which occasionally produces odd-eyed cats and some deaf cats. Although the dominant white gene – the one that makes all white cats – is the one that causes most deafness in cats.
In conclusion, white fur on domestic cat paws (aka ‘socks’) was a feature which pleased people at the time, say 5,000 years ago, so they made sure these cats bred to create more. I wonder if there were professional cat breeders in those days. I believe that there were. They certainly bred kittens during the time of the deity Bastet for sacrifice (c. 1070–712 BC).
Selective cat breeding is the method behind all of today’s cat breeds. This has taken many of the breeds far away from their genetic origins such as the Persian. Selective breeding has also altered the original appearance of some breeds such as the Turkish Angora and Van. The reason? Because breeders believe that they can ‘refine’ a cat’s original and natural appearance. This is a dangerous process as aesthetics are in the eye of the beholder. Also a lot of people like the uniqueness of the original cat rather than some souped up artificial creation cooked up in the backroom of someone’s detached home in Florida.
SOME MORE ON THE PIEBALD GENE: