Living together

Abstract

Abstract One of the themes of this book is that complex organisms depend on a division of labour between their parts. But this end result can evolve in two very different ways. Compare, for example, an elephant and a plant cell. An elephant depends on co-operation between different kinds of cells—epithelial cells, muscle cells, neurones, and so on. These cells have essentially the same genes. They are derived during development by the division of a single fertilized egg. In evolutionary time, they are all descended from the same single-celled ancestor. The differences between them arise not from possessing different genes but because influences external to the cells cause different genes to be active in different cells. The division of labour in human society, or between castes in an insect colony, is analogous. Humans, although not genetically identical, are very similar, and have a recent common ancestor. The differences between a carpenter and an electrician are caused not by their genes but by their training. The evolution of such systems—multicellular organisms, and animal and human societies—is not discussed in this chapter: it is the topic of the remainder of the book.