The idea that there is a tendency of organisms towards a progressive increase of complexity of bodily organization was already present before the rise of evolutionism. With the acceptance of evolutionary theories, many naturalists, especially those working with fossils, embraced the occurrence of such a tendency in the evolutionary process. This new way of approaching the idea of progress in nature received various interpretations up to the time of the emergence of the modern evolutionary synthesis, which left little room for the existence of another guiding element of evolution different from the one proposed by Darwin.
Progress; Complexity; Body organization; Evolution; Fossils