What if your actions affected 1,000 other people? Would your behavior change? What if you did not even know the people affected — would that make a difference?

Floodwaters in Atlanta wreaked havoc last week. Schools closed, Interstates closed, cars were abandoned after stalling in water, and people died from being washed away or drowning in rising waters. Bass boats motored over streets and parks covered with water. A friend paddled his Ganoe boat to rescue neighbors and their pets, paddling into the living room of one neighbor's home to help a family.

Homes were destroyed, and lives were lost.

After the destruction came the response of a network of friends, acquaintances and even strangers.

Last Friday, my family and I planned on eating dinner at home to save money. But late in the afternoon, I received an email and learned about the plight of a nearby family whose home had flooded. It outlined ways to help, one of which was to patronize their restaurants (they own two). I forwarded the email to my husband, and we decided to join our neighbors for dinner at one of their restaurants, "Key West Seafood."

When we got to the restaurant at 6:30, business was slow. An hour later, the restaurant was packed by customers, most of whom were there as a result of the email. There was a line out the door, our order took over an hour to fill, and the waitress was doing her best to serve the meals as they became ready. Friends pitched in to help at the register, and a judge ran to a nearby liquor store to purchase more inventory.

The next morning, I received a second email, forwarded from my neighbor. The owner had sent out a note of thanks. The family was overwhelmed with gratitude for friends, neighbors and, in our case, even strangers helping them in their time of need.

We did not know the family, but had friends who did. Our actions were the result of information coming from our network of neighbors. This is often how activity and action spread, but the question is: How does it work?

A new book, "Connected: The Surprising Power of Social Networks and How They Shape Our Lives," by Nicholas Christakis, M.D., Ph.D. and James Fowler, Ph.D. (Little, Brown and Co., 2009) explains how social networks form and operate. It provides scientific studies and theories in areas of health, finance and social interaction. Continued...