Evolutionary change in agriculture: the past, present and future

In this special issue of Evolutionary Applications, we draw together a series of diverse studies that provide a sample of some of the ways in which evolution driven by both conscious and unconscious selection by humans has shaped the development of modern agriculture. Agriculture has been a crucible of evolutionary change ever since its inception thousands of years ago, and this change permeates agricultural endeavours at all levels of biological organisation, ranging from the individual gene through to whole communities. Agro-ecosystems thus provide one of the most cogent examples of situations where anthropogenic effects are major determinants of biotic interactions within and among species and communities, suggesting a central role for the application of evolutionary principles. This is particularly the case, given global concerns regarding food production and food security, and increasingly, the expectation that agricultural productivity gains must be achieved with greater efficiencies, and reduced environmental impact. In the development of human society, the shift to a relatively settled way of life from a nomadic hunter-gatherer life-style was enormously profound, and made possible only by the development and adoption of early agricultural practices. In turn, this change in human life-style had major impacts on the environment of agriculture and hence the traits and characteristics of plants and animals that were favoured both consciously and unconsciously by humans. Very often traits suited to species growing without human protection/husbandry were not suitable for agriculture and were rapidly lost (e.g. seed shattering), while others were specifically favoured by the more protected environment agriculture provided, and increased in frequency (e.g. seed retention). As agriculture developed, the environment of the field and paddock became increasingly differentiated from that of the natural environments in which plants and animals originally evolved. For plants, nutrient availability generally rose, plant density and genetic uniformity increased, and the balance in competition shifted from inter-specific considerations to intra-specific ones (particularly with the general reduction in species diversity). Tilling and crop rotation were further agronomic practices that were introduced partly for fertility reasons but also for control of natural enemies, as rotation causes shifts in whole fungal pathogen communities. It is interesting to note that another generation of changes to tilling practices – minimum tillage – is to some extent now altering ecological and evolutionary interactions at the plant–soil interface towards a different set of fungal control issues. Similarly for animals, domestication created a more predictable environment with increased resource availability during harsh times and protection from predators, but increased threats from contagious diseases, all subtly influencing the evolutionary make-up of our livestock. Over the last few thousand years, domestication, selection and hybridisation, both unconscious and conscious, has also led to significant changes in the appearance of plants and animals and their nutritional value. Examples are seen in virtually all plant and animal species that are farmed. In horticulture, this diversity is often highly prized in the form of different varieties that are preserved for subtle variations in flavour, texture or simply appearance (e.g. in potato, tomato, apple). In a similar way, extensive selection in farmyard fowls (chickens, ducks, geese and turkeys), and in pigs, sheep and cattle have given rise to very many distinctive breeds that differ in milk production, flesh texture and flavour, and obvious appearance, as well as in less obvious traits, such as patterns of social behaviour. Extensive agriculture has also seen similar major changes that have resulted in significant increases in yield and productivity. In plants, perhaps one of the most dramatic changes to have occurred within a species is found in the emergence of modern high-yielding hybrid maize from its close relative teosinte, and the subsequent application of a number of induced mutations and the introduction of an F1 hybrid system. Similarly dramatic changes have occurred in meat and fibre production and quality in selected beef and sheep varieties respectively. In essence, throughout the history of agriculture, changes in agronomic and animal husbandry practices and in the crops and animals being farmed have had Evolutionary Applications ISSN 1752-4571