Question

Coyotes and dogs have been placed into different species. however, they can mate and produce viable, fertile offspring. what would explain this?

Answer 1

That fact can be explained by the similarity in their genes.

Dogs and coyotes are from the same class, family and genus (Mammalia, Canidae, Canis).
This is almost enough for their offspring to be viable. But if the DNA is similar (which it is) offspring the chances of viable and fertile offspring is high almost at 100%.

Hope it helped,

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