TheAskerMan

Ok. So here's what I'm gathering. I always viewed a species as having a unique set of genetic possibilities that allows variation in traits, but not entirely new traits. For example, a whale can vary in size and color, but it cannot spout legs. Nor can traits vary beyond a limit. For example, a mouse can vary in size, but it cannot grow too big (like the size of a rat). For a mouse to be able to grow that big or for a whale to start developing legs would need genetic mutation because the current genes just don't have that capability in them; they don't have a "develop legs" command or combination.

That's what I thought. But you're saying there doesn't have to be genetic mutation for such a change to occur? It is within the mouse's genetic ability to gradually adapt through selection to become a rat without changes in genetic structure? Or am I way off in my understanding of genetics?? If species are a continuum, then when does sperm stop being able to fertilize an egg? When does that incompatibility occur?

I'm sorry. I haven't taken biology since high school. I'm just trying to get a layman's understanding of how the process works.

Ok, so genetic mutation is what causes a new species to emerge. But wouldn't a male and female have to be born at the same time with the same mutation for a new species to begin? Are there any documented instances of this happening or is it just assumed based on comparisons of DNA in different species?

I understand that things like geographical barriers can separate groups of a species and cause the groups to develop different dominant traits. But I don't see how this could cause a change in species. Pigs stranded on an island might develop a tendency to be tall so as to reach certain vegetation, but this is a change in dominant trait, not in genetic structure. How would the DNA and number of chromosomes of these pigs change?