Egad this has cost me so much effort (mea culpa -- I procrastinate a lot)
About 10,000 years ago, people in the Middle East started to develop agriculture. This was known as the Neolithic Revolution. People began living in one area and domesticating animals - a marked difference from the hunter-gatherer lifestyle. The Neolithic Revolution occurred separately in different parts of the world over the next few thousand years.
As agriculture improved, food became more readily available and population size increased massively. People began to live in larger groups, eventually forming villages, towns and cities.
With larger settlements came new forms of leadership. Whereas hunter-gatherer societies are thought to have been largely egalitarian (1), agricultural societies began to have more complex, powerful forms of leadership, such as kings, lords and chiefs.
Because people spent less time in search of food and lived in one place, labor became more specialized. Instead of everyone working in food production, people began to have jobs like farmer and artisan, resulting in the creation of new art forms like weaving, pottery and metallurgy.
One negative effect of larger societies was the beginning of inequality. As people grouped themselves according to status and profession, amenities were no longer equally distributed -- those holding higher positions often had more resources than those "below" them. This lead to class systems, poverty and wealth inequality.
Another negative effect of agricultural societies was that gender roles became far more rigid. Women often had less power than men, and were confined to household tasks and caring for children.