Can the frozen plasticity theory explain the existence of evolutionary trends?
The frozen plasticity theory also offers a new explanation for the existence of evolutionary trends, the slow directional phenotypic changes in organisms of particular phylogenetic lineages which endure much longer than the individual species involved. The main problem with the existence of such trends is that they are too slow to be geared by natural selection. The change in the value of the trait per generation is so small that it is absolutely invisible for natural selection. According to classical evolutionary theories, the selection pressure has to be strong enough to overpower the effect of genetic drift. However, such selection should result in far more rapid evolutionary changes than those which come to light as evolutionary trends in the paleontological record. The frozen plasticity theory suggests a new solution to the problem of very slow evolutionary trends. According to this theory, the trend could in fact be a product of a relatively strong and long-term selective pressure to which species can respond, however, only in short and rare periods of their evolutionary plasticity.