Talk:Night Light/@comment-38690747-20190303025748/@comment-38752401-20190309061708

If Night Fury's and Light Fury's were completely different, distantly related species in the same genus this would likely be true. However it is highly likely that Night Fury's and Light Fury's are subspecies or very close separate species. If they are either of the latter two, then the Night Lights would be fertile and perfectly capable of reproducing, and the same would be true for all of their possible descendents.

So to help this make sense, I'm going to use some examples. You bring up donkey's (Equus Africanus Asinus)  and horses (Equus Ferus Caballus). The reason that the offspring of this pairing is infertile is due to the different number of chromosomal pairs. Donkey's have 31 chromosomal pairs which equals 62 chromosomes. Horses have 32 chromosomal pairs which is 64 chromosomes in total. Which means that the hybrid offspring receives 31 chromosomes from the donkey parent and 32 chromosomes from the horse parent leaving them with 63 chromosomes, which means one chromosome is floating around (not literally, mind) without a pair. It's this odd one out that disrupts meiosis and makes the individual infertile.

Wolves (Canis Lupis) and dogs (Canis Lupus Familiaris) are subspecies and are fully capable of producing viable offspring. For example there is the, German Shepherd which has up to 10% Wolf, and the Saarloos Wolfdog has around 40% Wolf, as well as many more recent wolf dog crosses. Wolves (Canis Lupus) and Coyotes (Canis Latrans) are classified as separate species and are genetically distinct however they are still close enough that they can and do produce viable young. The reason is that wolves and coyotes as well as dogs, dingo's (mind that both dogs and dingo's are subspecies of the wolf) and golden jackals all have 39 chromosomal pairs, 78 chromosomes in total. This is the major reason why they can all reproduce with each other and still produce viable offspring. Bengal and Sumatran Tigers are also capable of interbreeding and producing viable young because they are subspecies. Humans themselves interbred with Neanderthals many thousands of years ago and those of European or Asian decent tend to have 1-2% Neanderthal DNA whereas pure Africans have 0%.

This is why the Night Lights are most likely fertile and capable of reproduction if the article is correct in calling them closely related species in which case they are more comparable to wolves and coyotes than horses and donkeys. It is also possible that when their species were being hunted towards extinction, the last of the Night and Light Fury's retreated to the safety of the Hidden World. Remember, Toothless's mate knew where it was, suggesting that she had been there before. There would only have to be a combined total population of 40 individuals for the Night and Light fury's to survive and prosper, even if only in the form of the hybridized Night Lights.