Well, my relationship to humans went down the drain as a kid...but, growing up in a rather conservative Household, being always told " the right one will come" I believed I was "normal" and the attraction to canines was, in technical terms " just like a noise on an empty amplifier input"..I started to meet people online and with 30 I had the chance to be intimate with a woman. And it was a shock for me to discover that I really liked that person but nothing worked. Look, feel, smell..nothing at all and when I tried to eat her out, -for me- that smell and look was so unpleasant that it was not possibe. At the same time, with a canine, it was a pleasure. So it was confirmed that it is an orientation. You do not wake up in the morning, being exclusive, it usually happens very early and it takes some time to develop like any other orientation.