I doubt anyone is born with any particular phobias. Perhaps there are a few extreme examples of a particular phobia which can be attributed to mental illness, but I imagine that would be rare.
As a child I personally was deathly afraid of snakes. Why is that? Well, the first major motion picture I saw in the theatre was Indiana Jones. He didn't care much for snakes either, and he was a big rough tough hero type. Also, where I grew up, out in the country, we had snakes, poisenous and otherwise around the house. It was not uncommon to find a copperhead in the yard. Repeated warnings by family (which was warranted) undoubtedly fueled this fear.
Now, the question is. . . if I was born an Inuit (Eskimo) child, and grew up never seeing a snake, would I have developed this fear? Likely not. Without learning that the snake represented danger, there would be no basis for my fear.
People with genuine homophobia no doubt had to learn this from somewhere. Without some obvious outward sign of dangerousness, children tend either not to fear these things, or fear everything (overprotective parents maybe?). I see on Animal Planet over and over again, children finding dangerous snakes in their garages, etc. . . These kids often show no fear of the snake, even if it is a giboon viper (egad!!!) or a constrictor large enough to kill the child.
Those same kids would likely be afraid of a big aggressive dog cause they have experience with dogs, and can detect from the dog's behavior he means them harm. This goes to respond to the lady who wanted an explanation of why her 9 year old is still afraid of lightening. Lightning is bright, big and fast, and the thunder associated with it, is loud and powerful. These things are startling even to an adult, and to a child, who is small and relatively powerless, big, loud powerful things are scary. Nothing complicated about it.
And by the way. You should be scared of lightning. It is very dangerous, and could kill you. That kid is smart. My guess is cave men who were not afraid of poisenous snakes and lightening, likely did not live long enough to pass these traits on to future generations.
B.