In my experience it can be both....learned behavior and genetic. If one of the parents is a high strung, "nervous nelly", and the other is calm, laid back and outgoing, there may be a kitten in a litter who will inherit a nervous temperament. Especially in the domestic cat who has been born as a feral, a nervous temperament and quick reflexes are good for survival, as the cat is more aware and vigilant and gets itself out of danger sooner than a laid back cat. With purebred cats that are bred as much for their beauty and uniqueness but also for their health and temperament, you don't see quite as many skittish nervous cats. Most conscientious breeders handle their kittens from birth and make sure they are well socialized with other cats, dogs and people, so the environment in which they are raised is beneficial to raising an outgoing, laid back cat. This education of the cat carries on if it goes to cat shows. Unlike dog shows the owner is not at the end of a leash, the cat really shows itself. It needs to have a very calm and even temperament to succeed in winning its championship or grand championship. So shows are a way of testing a cat's temperament. If you've ever attended a cat show it is noisy, usually a big crowd of people constantly passing by all the bench cages, talking to the cats and their owners. Then the cat's walked through a lot of people to get to the judging ring, and is put in a cage behind the judge, the owner leaves, and then it's picked up by a complete stranger who feels the cat's bone structure and musculatore, stares into its eyes to observe color and shape, and checks its coat. At some shows this same cat may have to go through this procedure six times, if there are that many judging rings. Then if it's called up for "finals" (1st to 10th place), it goes through the whole judging procedure again. The goal of a good breeder is always to improve the breed and to be as close to the show standard as possible for that breed. Good breeders will try to breed the best to the best, and so the perpetuation of genes for a good temperament is carried on. Occasionally at cat shows you do see a few with a nervous temperament or one that becomes aggressive with the judge because they can't tolerate the noise or change and smell of other strange cats, but they don't usually make the finals.
Some nervousness/skittish is learned. Recently I moved house and my girl Alkee always was the door greeter, but she became quite upset with all the changes with the moving, and with a lot of work done on the new house, and workmen coming and going and now when she hears the doorbell ring, she takes off for one of the bedrooms to hide out until they leave. Never used to do that before.....so sometimes it can be a single incident that can set them off.
Some nervousness/skittish is learned. Recently I moved house and my girl Alkee always was the door greeter, but she became quite upset with all the changes with the moving, and with a lot of work done on the new house, and workmen coming and going and now when she hears the doorbell ring, she takes off for one of the bedrooms to hide out until they leave. Never used to do that before.....so sometimes it can be a single incident that can set them off.