Each individual cat has its own unique personality shaped by many different factors. Most of these influences can be categorized as either nature or nurture.
Nature refers to the cat’s genetics and biochemistry. In other words, it’s like the hardwiring for your cat. Several years ago, Dennis Turner, a behaviorist from Switzerland, discovered a paternal effect on cats’ friendliness to people. Turner found that friendly cat fathers tended to produce friendly kittens. Since the feline fathers never even spent time with their kittens, Turner concluded that the connection must be tied to inherited genes.
A similar thing could be at work with your cat that is more anxious and skittish. Your cat might just be more prone to behave this way. Additionally, female cats are sometimes a bit more wary than males, though they can be quite loving and devoted once they grow to trust others. This is because females evolved more protective behaviors to care for kittens.
Nurture, on the other hand, refers more to the life experiences of your cats. This can include everything from how they were raised to what goes on in their lives on a day-to-day basis. Pay attention to how your cats interact. Do they all get along, or do the others often bully your more skittish cat? If your anxious cat is a victim of bullying, you might have to step in to help it out.
Numerous reasons — including your cat’s genetic history, environment, sex and more — can therefore help explain why one cat within your trio acts so differently from the others. Since you can affect the nurture aspects, I hope that you can work to de-stress your cat’s life soon.