Consider the probabilities? How many sperm did your dad produce during his lifetime? How many eggs did mom have? If you are the result of one egg and one sperm, then out of the trillions of spermatoza that your dad made and the thousands of eggs that your mom had, we are already way beyond the odds of wining the lottery. Now, consider your parents, your grandparents, great-grandparents, etc. Of course, human population decreases as we go back in time, so, eventually, cousins are having sex with other cousins.
To simplify things, I could have been "Dawn" but, instead, I was "Don." That's a 50-50 probability, roughly. No dig deal, but apply the same logic to your father, and his father, and his father, and his father. It is like flipping a coin 100,000 times or more and getting all heads! If your dad (or his dad or his dad or his dad, etc.) had been "Tammy" instead of "Tom," you would not exist.
This is why Dawkins says (paraphrasing), "It some dinosaur had sneezed next to another one, we would not exist." If evolution is true, you should not exist. The probability of you existing is infinitesimal.