Thank you very much for your detailed explanation. I'll read the links you've provided, and more on the subject. > A variation that happens through a mutation

Thank you very much for your detailed explanation. I'll read the links you've provided, and more on the subject. > A variation that happens through a mutation doesn't need to be present in both breeding partners for it to survive. Indeed I didn't think about dominant genes... Thanks for pointing that out. However, I was more along a way of thinking which seems to have been disproved recently, as Wikipedia suggests: "Until recently, there has a been a dearth of hard evidence that supports this form of speciation, _with a general feeling that interbreeding would soon eliminate any genetic differences that might appear._ [example follows]" [1] 1. http://en.wikipedia.org/wiki/Speciation http://en.wikipedia.org/wiki/Speciation > 2) The notion that each species has an ecological niche is false. Exactly. I wonder why we have missing links among species. That is: why we don't have more half-bird-half-reptile around? They should have got along quite well with each other. IMO, if evolution were to bring speciation, I would have expected more of "a mess" of species around us. > 3) There's a lot of things that species could do but aren't doing. I was arguing that since - AFAIK - scientists think that life originated in water, why would animal lose the ability to get oxygen from water? Thas looks like losing an evolutionary advantage to me, and out of line with my understanding of evolution, which is deemed to be gradual: it would have had more sense becoming able to breath air while still being able to breath water. Were are species able to do both (the missing links)? Thank you very much again for having spent your time in making me more knowdlegeable.