Suppose that a single specie of sheep is gradually separating into two, and that the two parts learn to graze separately on opposite sides of a large mountain. Call the two extremes the Left (L) population, and the Right (R) population. There is never a 0% Fertility Ratio (FR) between L and R, at these extremes of contact, as they diverge for some length of time, yet have not become 100% relatively infertile. That is to say, if we arbitrarily bring together members from each of L and R, there won’t be COMPLETE INFERTILITY for a long time. Maybe there will be a 30% success in fertile offspring, or FR, at 10,000 years. As the separation time becomes longer, there may be only a 10% FR, then a 3%, then a 1%. Finely, the FR becomes identically zero. Do we have all of a sudden, a new specie? Would you call the population R, having a FR of 30% with respect to (WRT) the L, a new specie? What about at the 10% or 3% FR’s? You see, there is no smooth transition between the FR’s of 100% and 0%. Consequently, the TRANSITION TO A NEW SPECIE is not in discrete steps, but is a quasi-continuous process! It is at these, in-between, times that some want to call TRANSITIONAL FORMS (TF), but what if I take the in between point of these extremes, the Center (C). Those in C will evenually have an FR of 0% WRT both L and R. But at some time before that, it will interbreed with an FR that is greater than 0%, but less than 100%, with each end. Can you see where this is going? We can talk of the transitional steps, all-right, but the concept of SPECIE is far from a discreteness that must be forced into Nature’s vocabulary!
Charles
™ Version 4.2