Much of the discussion consists in ignoring the main point. Thus Morris mentions recent discoveries of biochemical similarities among organisms. This… - Philip Kitcher

Evolutionary change is change in the genetic constitution of a population. This type of change can come about as a result of a number of factors. Immigration and emigration of organisms will bring new alleles and new allelic combinations into the population and will cause others to disappear. Mutation will lead to the formation of new alleles. The major claim of a Darwinian theory of evolution is that the principal factor of change is natural selection: The most important evolutionary changes come about because some allelic pairs are fitter than others, and these obtain greater representation for their constituents alleles in subsequent generations.

It is hard to resist the impression that all these computations are designed to bamboozle those who become weak at the knees at the sight of numbers.

Barnes and Morris both choose processes that we know to operate at different rates at different times, and then use the observed rates to estimate the time at which the process began. Dating the past is a complicated and technical business, and one cannot ignore the technical details simply to generate the ages one wants. Without a thorough understanding of which rates are constant overtime and which rates fluctuate wildly, Creationist dates are bound to be stabs in the dark. However, Creationists know what they want the age of the earth to be. So just as in the case of the second law of thermodynamics, important parts of science are abused. By carefully picking a process on the basis of its ability to give the desired result, without attending to the question whether it is reasonable to think that it happened at a constant rate, Creationists attempt to convince the uninitiated that their blind dates have scientific references. Nobody should be taken in.