Actually, it's quite possible (even likely) that most speices are not in a process of change most of the time. The rate of evolution is not constant, and may be very close to zero for many creatures for very long periods of time (on the order of tens of millions of years), followed by relatively short periods (on the order of thousands or tens of thousands of years) of evolution, followed again by periods of stasis.
But the problem arises here again.