The sparrow with four sexes
There's a diagram about halfway through that illustrates how this works. I miunderstood the article at first and was wondering why you wouldn't just say that there are two species, but the diagram sorted me out. The tan stripe birds almost always mate with the white stripes, and the offspring have a 50/50 chance of having the mutation.<p>I wonder if the birds instinctively "know" that they have 4 sexes