How Species Are Formed

Abstract

The preceding chapter was devoted to macro-evolution, the kind of evolution which over long stretches of time produces obvious differences: a historical and unrepeatable process. In this chapter we turn to evolution as it is revealed by a magnifying glass: evolution in full action, happening at the taxonomic level of species or even lower, where processes, in principle, do allow experiments. On this level, as far as herbaceous plants in temperate zones are concerned, Stebbins (1950) has assembled a large amount of knowledge in his classical work. For forestry purposes, several species of trees with commercial value have been studied, although their long seed-to-seed cycle makes this considerably more difficult than in the case of herbs. In a rain forest the problems are still greater. Trees in botanical gardens, which are always single examples, are of no use whatsoever if one wants to know what happens in the forest itself, where trees of one species are often few and far between and do not always flower at the same time.