While the use of stone tools began 2.5 million years ago, it wasn’t until about 10,000 BCE that Homo sapiens applied these tools to the deliberate cultivation of plants and animals. The adoption of sustained agriculture – what anthropologists call the “Neolithic revolution” – signifies an important turning point in the development of human societies, as it led directly to population growth, permanent or semi-permanent settlement, as well as technological and social development.
 Neolithic agriculture developed at different times in different parts of the world, beginning with the Levant and Mesopotamia, followed by Northern Africa, Southeast Asia, and Europe. But while we often call it a “revolution,” it would be a mistake to believe that agriculture was a sudden and complete development, an all or nothing proposition that societies adopted wholesale at the first opportunity. Instead, it developed slowly, beginning as a supplement to more traditional hunting and gathering lifestyles in which people relied on plants and animals gathered or hunted in their natural environment. Over time, as people learned more about and relied more greatly on domesticated plants and animals, they settled more permanently and cultivated the land more intensively.
 Neolithic farmers collected and planted seeds that they learned would produce palatable grains, selectively breeding plants that were deemed healthy and delicious, and avoiding those that were not. Early agriculture was restricted to a limited number of plants, namely Emmer wheat, Einkorn wheat, and barley. Later, people learned to cultivate pulses, including lentils, peas, chickpeas, and bitter vetch, as well as the multi-purpose flax plant. Together, these eight plant species are known as the Neolithic founder crops or primary domesticates.
 People’s success in planting, cultivating, and harvesting these plants came about as a result not only of their increased knowledge of the plants themselves but also of the conditions for growth. They explored innovative irrigation techniques, which enabled even greater production and, eventually, food surpluses. Of course, food surpluses are useless unless people have the ability and facilities to store them, which people did in granaries. And food surpluses, in turn, enabled a host of other social developments, like occupational specialization (since not everyone had to be involved in food production), trade, and social stratification.
 These advances in agriculture went hand in hand with technological development. People fashioned stone tools such as hoes for working soil, sickle blades for harvesting the crops, and grinding stones for processing the grains. More important than such agricultural implements, however, was the polished stone axe, which allowed the Neolithic farmers to clear forests on a large scale and open up new lands for cultivation. Along with the adze, the axe also enabled them to work the trees they felled into wood that was usable for building shelter and other structures.
 Besides cultivating plants, these stone age farmers also domesticated animals. At first, it was sheep, goats, and dogs whose temperament, diet, and mating patterns made them good candidates for domestication. Later, cows and pigs were added to the mix. Besides meat, these animals provided people with milk (a renewable source of protein), leather, wool, and fertilizer. Cows became valued for their labor, as they assisted with plowing and towing, and dogs provided protection (not only to humans but also to their crops and livestock) as well as companionship.
 That agriculture enabled hitherto unknown population growth is undeniable. Food surpluses and an agricultural lifestyle brought a security and safety that nomadic hunter-gatherers did not enjoy. And it may be argued that the subsequent advances in all realms of society – not only the aforementioned technology but also knowledge, art, writing, astronomy – would not have emerged without a sedentary lifestyle. But the impact of the Neolithic revolution, often heralded as a giant step forward for humankind, was not all positive.
 Sedentary agriculture narrowed the diet of Neolithic peoples: they consumed greater amounts of starch and plant protein and fewer types of food overall. An increasing number of researchers are claiming that human nutrition became worse with the Neolithic revolution. In addition, disease increased, as humans lived in closer contact with each other and with domesticated animals; sanitation didn’t advance quite as quickly as agricultural methods. It also turns out that agriculture required significantly more labor than hunting and gathering. The combined result of these facts was a life expectancy that was most likely shorter than that of the apparently more primitive hunter-gatherers.