Abstract: This chapter reviews new research findings that are changing our ideas of the nature of genomes and of biological species. All genomes, from bacteria to humans, are constantly changing with DNA being added and lost, frequently between different species. Some species, including many crops, contain over 90% non-coding ‘extra DNA’. This DNA was originally believed to be parasitic or non-functional, but is now increasingly recognized as having many important roles in the development of organisms from rice to humans. Thanks to molecular genetics, the species concept is becoming less useful, especially in many plants, as the increasingly blurred boundaries between supposedly distinct species are recognized. It is now clear that the detailed genome organization of our major crops, particularly the close physical linkages between domestication syndrome genes, was a major contributor to their amenability to cultivation by early farmers.

Keywords: mobile genes, extra DNA, gene transfer, species concept, genome rganization, early farmers, domestication syndrome, gene clustering,