Most people, even the creationists I debate, when they think about it, have no problem with the idea that genetic characteristics in a population change over time. The existence of different human races supports this idea.
Closer to home, it is my own perception that people seem to be taller now that they were when I was in high school (more than four decades ago). My high school graduating class had over 900 people in it. Yet our high school basketball team had one player who was as tall as 6’-5”. He was a veritable giant in the athletic conference in which my school competed. None of the other schools in that conference – each of which also had hundreds of students – had anyone that tall. Yet, in the current year, many high school basketball teams have players 6’-5” or taller. While someone 6’-5” still stands out as unusually tall in the general population, it has become a fairly common height among high school basketball players.
Certainly that just reflects my own experience and I can’t provide definitive statistics to support my claim (though I believe that such statistics exist). Moreover much of that increased height is most likely due simply to a better diet rather than to genetic change. Nonetheless we are talking about perception and if you point out examples like those, I find that many people share my perception that genetic change does take place in populations of individuals over time.
A creationist will immediately point out that those taller people are still just that – still people. They acknowledge that smaller amounts of genetic change (which they call “micro”-evolution) surely takes place but they insist that evidence for larger amounts of genetic change (which they call “macro”-evolution) is lacking.
But the question then becomes this: if genetic change in populations is easy to see and believe in, what barrier is there which would prevent that genetic change from accumulating over long enough periods of time so that it would allow ANY amount of variation? In other words, if you insist that it is impossible to get from point ‘A’ to point ‘B’ in anything, then you must demonstrate a barrier.
An analogy could be made to driving a car. We could call driving within a particular state “micro”-driving (change within a state) and driving from one state to another as “macro”-driving (change from state to state).
It is easy to demonstrate “micro”-driving. You merely have to watch the traffic on any freeway (except during some extreme traffic jam) to acknowledge that people can drive within a state.
What barrier, other than time, exists that would prevent “micro”-driving from becoming “macro-driving (i.e. driving a car to another state)?
There is no such barrier.
I am writing this in Minnesota. From where I write this, the closest state is Wisconsin – about 50 miles away. I doubt that anyone would dispute the fact that I could jump in my car, get on an appropriate Interstate Freeway and be in Wisconsin in less than an hour.
The only factor preventing “micro”-driving from becoming “macro”-driving is time because there is no barrier, apparent or otherwise, preventing me from driving to that adjacent state. I would take close to an hour to do so, but nothing would prevent it. So time is the only factor.
In some cases, of course, a barrier that would prevent “micro”-driving from becoming “macro”-driving could be demonstrated. I can’t drive from California to Hawaii because of such a barrier. That barrier is called the Pacific Ocean.
In the same way, once someone accepts the fact that genetic change takes place in populations, they can’t really dispute that “macro”-evolution also takes place – if given enough time – until they can propose and demonstrate a barrier to the continued accumulation of genetic change. In other words, people who accept “micro”-evolution but dispute the existence of “macro”-evolution must show a genetic version of the Pacific Ocean.
There is no evidence that such a thing exists.
Some creationists insist that the barrier is the Second Law of Thermodynamics - that all change is “downhill”. Yet they accept some “uphill” change in micro-evolution. So their argument is clearly inconsistent.