Yes, we need to draw a line and the question seems flawed. Sure, it makes you think, it is funny, but it contains an invalid assumption that the line's width i

Yes, we need to draw a line and the question seems flawed. Sure, it makes you think, it is funny, but it contains an invalid assumption that the line's width is a single generation. If we assume that the question is about species, it takes thousands of generations for an offspring not to be able to reproduce with its ancestors.