Microevolution- evolutionary changes that result in differences within a species or genus.
Macroevolution- series of microevolutionary changes that result in a new genus, family, order, etc...
The other day, a naturalist claimed that no such distinction is necessary. The argument is that there is a long string of microevolutionary changes from species to species, from genus to genus, family to family, etc...; macroevolutionary changes are a series of microevolutionary changes that result in a new species, genus, family, etc...; thus macroevolutionary changes are really the same as microevolutionary changes over time. Since they are ultimately the same, there is no need to distinguish between the two terms. This person further claimed that even if they allowed the distinction in terms, the fact that small changes over time is undisputed, means that many changes over time is proven; microevolution is undisputed, therefore a lot of microevolution (macroevolution) is proven.
This seems pretty solid. Every premise is true, and the logic is valid. But, there is one unstated premise. Macroevolutionary changes are a lot of microevolutionary changes, but they are in a specific series that follow a specific pathway. The missing premise in this argument is that the pathway from ancestor to claimed offspring (many generations down the road) is clear of obstacles.
In his book, "The Edge of Evolution" Michael Behe shows that scientists have observed such an obstacle in the lab. The obstacle was not time, it is in the genetic pathway that must be traversed if macroevolutionary changes are to take place in reality. Since an obstacle has been observed, we now have a false premise in the argument. Since there is a false premise, the argument fails. There is a difference between micro- and macro-evolutionary changes. A lot of microevolutionary changes are necessary for macroevolution, but they are not sufficient. The other sufficient condition (a clear genetic pathway) still has yet to be met. Since both sufficient conditions for macroevolution have not been met, it has not been demonstrated. And since changes over time has been demonstrated, there is a need to distinguish between the two. To prevent confusion about what we know to be true and what we don't, this distinction must be made.
There is only one way that this can be overcome by the naturalist: find a pathway that would be clear by default in nature. Notice that I have added one more piece to the missing premise above: "...clear by default in nature". I have to add that last qualification because as scientists are looking for a way to overcome this obstacle, they are introducing their own intelligence- fine-tuning the process, then "allowing nature to take its course". Their conclusion of naturalistic macroevolution will depend on a premise that is founded on intelligence. That would undermine the whole argument for naturalistic (macro)evolution. Even if scientists find this "naturally clear" pathway in the lab, it will always be tainted with intelligence. I do believe that that last statement will be investigated more deeply in the context of artificial life by biochemist Dr. Fazale Rana's next book "Creating Life in the Lab: How New Discoveries in Synthetic Biology Make a Case for the Creator".
The point is that even if scientists claim to find a naturally clear pathway (overcome the obstacle), we should investigate the claim more closely. The more scientists are involved in avoiding the obstacle, the more intelligence that is involved in avoiding the obstacle. The more intelligence involved in avoiding the obstacle, the less natural processes are involved in avoiding the obstacle. The less natural processes are involved in avoiding the obstacle, the more the obstacle stands naturally. If the obstacle stands naturally, macroevolution will remain unobserved and must be distinguished from microevolution.
In celebration of Darwin Day coming soon, please enjoy these other posts:
Why Darwin Day is Hosted By The Wrong People
I, Charles Darwin: Being the Journal of His Visitation in the Year 2009