Sometimes themes can be found in common across very different systems in which change occurs. Imre Lakatos developed a theory of change in science, and one involving entities visible at different levels. There are theories defended at a particular time, and there are also research programs, larger units that bundle together a sequence of related theories and within which many scientists may work. Research programs are competing higher-level units within a scientific field. Scientific change involves change within research programs, and change in the ensemble of research programs present at a time, where some will be growing, some shrinking, some progressing, some degenerating. These are also themes in biological evolution. Recent biology has often found itself dealing with the relation between change at a level of "collectives" – such as organisms like us – and change at a lower level – the level of cells, genes, and other evolving parts. This work is continuous with an older discussion, one that arose when biological evolution was no more than a vague speculation, round the beginning of the 19th century. What is the living individual? What is the basic unit of life or living organization? Questions like this were pursued by Goethe, by Erasmus Darwin, the grandfather of Charles, and many others. Initially it was plants, especially, that were seen to raise these problems, and then newly described marine animals with strange life cycles. The discussion was influenced by the rise of the cell theory in the early 19th century, but some writers looked for individuals well below the level of the cell.