This is one of those questions where the answer becomes clearer the more we learn about animals in a variety of fields such as genetics, animal psychology and animal behaviour.
Animals, just like people, develop specific fears as a result of learning. Animals learn to be afraid of snakes because they can be dangerous. For example, when a group of dingos meet a snake, the young dingos watch how the adults react. They learn to cry out, to tell other members of their family, to get out of the snake’s reach. They learn to be afraid. Learning to have a fear of snakes means that you will keep your distance, increasing your chances of not being hurt or killed by a snake.
Keeping your distance from snakes keeps you safer, which also means you have more chance of successfully having babies of your own (passing on your genes). This brings up the idea of whether the fear of snakes is genetic (a trait passed on from our parents) or innate (had from birth). Some research shows that the fear of snakes is a fear that humans have, even if they have never seen a snake. So, this fear must have developed at an earlier stage of our evolution and is still within us today(1,4). However, conflicting evidence from some studies show that very young children do not show a fear of snakes (2). So, we’ll just have to wait until we understand more before we can be sure.
Some interesting links/references with further information: