ABSTRACT
Various theories of evolution which have been advanced in opposition to Neo-Darwinism, as well as certain currently controversial aspects of Neo-Darwinism itself, have been reconsidered from the viewpoint of modern genetics. With advances in knowledge, the vitalist, finalist and creationist arguments are now even less tenable in the scientific view than they ever were. Geneticists are divided over the relative evolutionary importance of allelic states of loci versus restructurings of the genome, and evolutionists disagree about whether evolutionary events are smooth extrapolations from populational variation or occur as quite abrupt transitions. Since in no case is the origin and nature of variation of evolutionary significance known, any generalisation must await further information. As well as those theories questioning the materials of evolution, others are designed to minimise the random element in current evolutionary theory. In contrast to the vitalistic theories, which usually provide both a course and an aim of evolution, these ‘directional’ theories emphasise that any evolutionary advance determines to some degree the nature of future change. Evolution appears to progress by multiple mechanisms, varying in importance according to the organism’s genetic complexity or evolutionary status. With this in mind, it seems that some previously discarded theories should again be taken into account in developing modern explanations of the evolutionary process.
