Fevre Dream - George RR Martin

Another shameless plug of one of my favourite authors although this time I'm afraid I'm going to have to pull him up on some nonsensical biology, which put an infuriating tarnish on an otherwise excellent vampire novel.
Fevre dream tells the tale of a 19th centuryvsteamboat journey along the missisippi that acquires some unsavoury mythical guests. The book is actually very good and perfectly blends the feel of the deep south with horror.
One of the things I enjoyed about the book is the authors approach to the vampires in that he treats them as biological creatures rather than fantastical ones. To this end he goes to some interesting lengths to establish them as an off-shoot of humantiy - I won't go into details but half the fun is in discovering his "rules" for vampires.
There is one rule that upsets me though and I guess this is technically a little bit of a spoiler so you probably shouldn't read on from here.


AT
THIS
POINT
I
SHOULD
POINT
OUT
THAT
BLOGGER
COULD
DO
WITH
AN
EASY
SPOILER
TAG
FEATURE

ok still here? Then don't get upset if you think this is a spoiler.
So one of the "rules" of the vampires is that when they give birth they die. Now I'm sure it's meant to serve as a tragic notion but if you think about it, it makes absolutely no sense. Unless all vampires were female and occasionally had twins there is absolutely no way the vampire species could expand, In fact they'd essentially be halving in size every generation (assuming a 50/50 gender ratio). This is the kind of stupid reproductive strategy that would make a Panda jealous (let's not give them any ideas).
Now, i'm sure some people would say "you're reading a book about vampires, let it go" but I think when the author has otherwise done such a good job in making them believable this is an unfortunate mis-step. I guess most people just gloss over the statement and don't really think it through but for people like me it is really annoying.
To be fair I've created my own "internal logic" so that I can still enjoy this book for the great piece of fiction that it is. I've decided the dying in child-birth is a "recent" mutation in vampires. Females could have more than one child as the species expanded but for some reason this mutation became fixed. It's an easy fix and would have only required an extra sentence in the book. I'd like to think it was something that was edited out of the original manuscript.