From Bryn Glover
In their exchange about the species of dogs and wolves (Letters, 27 June) neither Ann Williams nor Michael Slezak mentions the need for offspring to be fertile, which was my understanding of the definition of a species. Mules are the healthy offspring of horses and asses, but they are infertile. I would be interested to learn whether the “woodles” – wolf/poodles – of Indiana can produce pups.
Glasshouses, North Yorkshire, UK
