I want to see what Spetner can SUPPORT with empirical evidence. It is an interesting idea, but one that has been falsified by observation.
But there is a large and ever-growing body of evidence that heritable changes do occur in living organisms that adapt them to their environments, and that these changes do not stem from simple errors in DNA replication. In the last decade and a half, we have seen mounting evidence on the molecular level of large genomic changes that confer selective advantage and occur just when they are needed. These observations have so far been made only on bacteria. Directed mutations are also known to occur in plants, and there is evidence that they occur in animals as well. These mutations are not random, but are apparently induced by the environment. They are not merely errors in DNA replication, but seem to be mutations of a totally different kind.
In 1982 Barry Hall reported on an experiment in which he prepared a strain of E. coli bacteria lacking the beta-galactosidase gene lacZ, which normally hydrolyzes lactose. When these bacteria grew and multiplied on another nutrient, but in the presence of lactose, they gained the ability to metabolize lactose, an ability that proved to be heritable. The gained ability was found to be due to the presence of a new gene. The new gene encodes a new enzyme that can perform the function of the beta-galactosidase, enabling the mutant bacteria to metabolize lactose. The gene was present all the time, but in a dormant state. It was turned ON by two mutations that occur in the presence of lactose and do not appear in its absence. Hall declared that the "normal function" of this gene is unknown, and he called it a "cryptic" gene.
Neither of these two mutations alone gives the bacterium any advantage, so there could not have been any selection for them separately. For the cryptic gene to become active, both mutations have to occur. In the absence of lactose, these two mutations are independent. They can occur together only by chance, and will do so with a probability of only about 10-18 per replication. If they occur at random and independently, the expected waiting time for one of these double mutations to occur in Hall's population would be about 100,000 years. But in the presence of lactose, he detected about 40 of them in just a few days! One can conclude that the lactose in the environment was inducing these mutations.
If DNA were built to mutate, then more than 1% of the population would get the same mutation in the same generation to adapt to a new environment. What we observe is that beneficial mutations occur at a much lower rate. A much, much, much lower rate.
You don't know what mutation rate might be designed into DNA. Perhaps its low for a reason.
Anyway, Spetner admitts that he's speculating at this time, but its still seems to make sense.