ABSTRACT
How has this immense organized complexity of life developed and what is its source? The theory of evolution is now established beyond question, but some controversy still persists over the ‘how‘ and the ‘whence‘. There can be no serious dispute over the main fact, revealed in the fossil record and by other evidence, that there have been major trends, and not much doubt about what they were. Life has evidently progressed from the relatively simple to the fantastically complex, from the lowly and minute to the larger and more elaborate, growth imposing the necessity of greater complexity. It has evolved from single celled creatures to metazoan and colonial types; from the less to the more completely individuated; from the aquatic to the terrestrial and aerial; from the Poikilothermie to the homoiothermic; from the instinctive to the intelligent, a progressive internalization and increasing auturgic control of the immediate conditions of living. That there has been such progress is not seriously disputed by scientists, but, as G. G. Simpson points out, the line of development has been neither straight nor single. It seems rather to have been a ramification and radiation of types at different stages along a zigzag course; yet through and amidst all this the major trends are distinctly recognizable. Moreover, unicellular and colonial organisms, aquatic, Poikilothermie and numerous relatively ‘primitive‘ forms still persist, and are not really primitive in that they are themselves products of evolution stretching back through lost and largely unknown genealogies. In several different ways past forms are preserved and carried on into present developments, sometimes as separate organisms and species that have been evolved along lines of their own, sometimes as subordinate and possibly vestigial components incorporated in more highly organized animals. With some exceptions (to which we may later advert) the progress has been one of complexification, but always as the correlative and concomitant of integration. It has been a progress of increasingly elaborate polyphasic unification of differences.
