In the 2nd episode of the new Cosmos series, the host Neil deGrasse Tyson shows how the white-furred bear could have evolved (reasonable scientific speculation, of course).
If you haven't seen that episode, here's the link. Great show, by the way.
So, it shows the bears eggs, and then goes on to show how there can happen an error in the DNA copying, that leads to the brown pigment production malfunction. Here's an excerpt from the subtitles text:
- great bears roamed the frozen wastes of Ireland. - This might look like an ordinary bear, - but something extraordinary is happening inside her. - Something that will give rise to a new species. - In order to see it, we'll need to descend down to a much smaller scale, to the cellular level, so that we can explore the bear's reproductive system. .. - Those are some of her eggs. - To see what's going on in one of them, - we'll have to get even smaller. - We'll have to shrink down to the molecular level. .. - When a living cell divides in two, - each one takes away with it a complete copy of the DNA. - A specialized protein proofreads to make sure - that only the right letters are accepted - so that the DNA is accurately copied. - But nobody's perfect. - Occasionally, a proofreading error slips through, - making a small, random change in the genetic instructions. - A mutation has occurred in the bear's egg cell. - A random event as tiny as this one can have consequences on a far grander scale. - That mutation altered the gene that controls fur color. - It will affect the production of dark pigment in the fur - of the bear's offspring.
From my (not professional but kind of passionate amateur) knowledge of biology, I I was under impression that all of the mammalian eggs are present at birth. But the story depicted in the show involves the (erroneous) DNA copying. I see dissonance there, and I'd like to solve it.