Sometime in the next few months, the proportion of the world's population living in cities will pass the 50% mark, if it has not done so already. Homo sapiens has become Homo urbanus.
Not until 11,000 years ago, around the end of the last ice age, did pockets of humanity come together in anything that might be called a village. By that time we had been around for about 120,000 years. It took another 6000, during the classical days of Greece and Rome, before cities of more than 100,000 people first appeared. Even in 1800 only 3% of the world's population lived in cities.
Most of today's cities are in poor countries and many, if not most, of their inhabitants live in slums. Some of the traditional things that drove our ancestors into cities no longer rive us. Some of what cities provided is now found in suburban malls or industrial parks. Security, once the main reason for huddling together, is often now more elusive in the violent streets of the metropolis than in the exurbs.
And technology, which has usually favored urban progress, now enables people to work in rural bliss on home computers. No wonder so many cities find that in order to flourish they'll have to reinvent themselves.