Simply put i don't think there is nearly enough of this. The best examples I've seen tend to have it be a result of some family curse or because of magic or lastly some experiment. What i seek is something where the pregnancy is allowed to happen because of some genetic anomaly on either side, aka natural. Heck I've had an idea for a story like that where the human female would be able to breed with any mammal as a result of this. But i keep hitting walls or end up repeating myself with each new animal.
