
wild dogs did or do tend to have one season and the more primitive breeds like the basenji are more likely to continue that way. The season is usually at the optimum time of the year to raise pups and have food available.
We are so used to our dogs having more than one people are often concerned if it a bitch doesn't have two seasons a year. No idea why a more developed, for want of a better word breed changed to ttwice though,. I guess its evolution , safety , better nutrtion etc , just educated guess. My flat coat was a one season girl too nothing to do with breed just her body but actually its more natural to their origins