Some 15,000 to 10,000 years ago, humans started seeding and harvesting plants and maintaining animals in order to augment the food they obtained from wild-growing plants and hunting. These seemingly simple activities set in motion a long-term process that has led to the dominance of agriculture as we know it today. With the exception of a few remaining hunter–gatherer groups, agriculture has now become the most important source of food for most people. Agriculture is also a major source of feed for animals and of fiber.

This transition from hunting–gathering to agriculture was without a doubt one of the most significant eras in the evolution of humans. It allowed food production on a more intensive and efficient scale than ever before, eventually leading to population increases, labor specialization (and especially a nonagricultural sector), the formation of villages, cities, and states, and the rise of more hierarchical societies and states (MacNeish 1991, Barker 2006).

Traditional Management of Biodiversity

The contributions to this section deal with the connection between biological diversity in agriculture and its social, cultural, and geographic contexts. Crop evolution is generally understood through the processes of domestication that generated cultivated species and allowed the transformation of human life ways. Domestication set the stage for the transformation of subsistence and human social systems. The success of this transformation required not only new species of plants and animals but also a suite of allied technologies, organizational innovations, and behavioral change. The establishment of agricultural systems involving technology, social and economic organization, and cultural patterns was no less an accomplishment than crop domestication in the transformations that emerged at the end of the Pleistocene.

While the origins of agriculture through the processes of domestication and organization of food production systems loom very large in the evolution of crops and human society, both crops and agricultural systems have continued to evolve, and this evolution is significant to such concerns as the conservation of biological diversity and to meeting future needs such as those posed by climate change. Crop evolution after domestication is marked by such things as diffusion and adaptation to new habitats and the diversification of cultivars. The evolution of agricultural systems is marked by the elaboration of human knowledge systems about cultivated plants, change in social organization such as the elaboration of hierarchy, and dynamic economic organization for the allocation of resources and the distribution of production.

Issues in Plant Domestication

The four contributions in this section illustrate the domestication continuum across time and space. While domestication started in specific areas (variously called centers of agricultural origins or domestication or even Vavilovian centers), it is now conducted outside these original areas as well. Likewise, domestication started roughly 10,000 years ago in association with the end of the last ice age, and is still practiced today by farmers and breeders. Each stage and location of agricultural development represents potentially different evolutionary factors that can shape the domesticated gene pools. Dissemination from the original hearths of agriculture undoubtedly brought into the picture factors such as selection for adaptation to new environments as well as genetic drift due to small sample sizes. Different cultivation areas also reflect different human cultural environments and, hence, distinct cultivation and consumption requirements.

Domestication of Animals and Impacts on Humans

I cannot imagine a compilation of manuscripts, as are outlined in this monograph, that would not repeat in one form or another, the notion that plant and animal domestication is the most important development in human history. Were this not true, then why even develop the Harlan II symposium? And yet, for all its well-accepted importance, so many crucial questions about the nature, direction, speed, and origins of these domestication events remain unanswered. However, as this volume so amply illustrates, now is a marvelous time to be a scientist (or indeed a nonscientist) with even a tangential interest in this topic. The chapters of this section, on the domestication of animals, and the impact of these events on human populations, bear ample testimony to this interest.

Uses of Biodiversity and New and Future Domestications

In previous sections, we have learned of new techniques to investigate prehistoric domestications of crops and livestock, new hypotheses of domestication and spread of crops and livestock in human cultures, and the genetic basis for domestication. However, domestication is not only a process of the past. In spite of the fact that currently a very limited number of plant and animal domesticates contribute to the world's sustenance, new domestications are taking place and given what humans now know about the process, there are opportunities for new domestications that should be pursued.

The number of plant species that humans have made use of is huge. One estimate is that 75,000 angiosperm species are edible; 7,000 of these have been used by humans as food sources (Myers 1983). A more recent review puts it as 4,079 food species (Proche?? et al. 2008), still a strong contrast to the few cultivated species that predominate today.

Early Steps in Agricultural Domestication

This part of our volume is about major processes governing the origin and dispersal of agriculture. The contributors are in accord on many issues, in particular that there is no clear break between hunting and gathering and agriculture, the latter arising from practices that develop naturally as hunting and gathering intensifies. David R. Harris (Chapter 2), who develops this argument most broadly via a global survey of hunter–gatherer plant and animal management and manipulation, concludes that the forager-to-farmer trajectory is essentially one of increasing geographical reliance on fewer species. Much more detailed treatments of hunter–gatherer intensification and its connection to agriculture in specific regions are presented by George Willcox (Chapter 4), Ofer Bar-Yosef (Chapter 3), and M. Kat Anderson and Eric Wohlgemuth (Chapter 8). Particularly striking here is the contrast between the richly documented accounts of plant use and manipulation in aboriginal California and meager archaeological evidence for what must have been equally intensive plant adaptation ultimately leading to agriculture in the Levant. In a nutshell, we know a good deal more about the details of intensive plant use in California, where agriculture did not develop, than in the Levant, where it did. The reason for these different trajectories remains unclear, as does a means for relating one to the other. Dorian Q. Fuller (Chapter 5) offers a methodological solution to the latter via analysis of a wide range of morphometric responses to human harvesting and manipulation (e.g., changes in seed size or shape) that are expressed well before a species is considered fully domesticated (e.g., nonshattering wheat). Dolores R. Piperno (Chapter 6) adds phytolith and starch grain size and morphology to the list of characters known to change directly in response to selection. In theory, such morphometric trajectories should index selective pressures connected with plant intensification and permit meaningful comparison between the “proto-agricultural” California and the agricultural Levant. Anderson and Wohlgemuth present some of these data for California. The problem here is that some species are likely more responsive than others.