"Whether you come to someone's aid depends mostly on your personality type," says clinical psychologist Antoinette Saunders. "Are you giving in general? Do you usually put yourself first? These factors all come into play, especially if the help is more than just a verbal exchange."
"I saw a motorcycle flip over the car in front of us and crash," she explains. "We stopped and called an ambulance, but it was amazing to me how many people just drove by.
"I think that for many, there's a part of you that feels it's not your responsibility, or that it's a hassle. That if you stop and get involved, you could get tied up in things you don't want to get involved in."
But if you do get involved, science says it could improve your health.
"When you get help or when you give help, your brain changes," says Thea Singer, author of "Stress Less: The New Science That Shows Women How to Rejuvenate the Body and the Mind" (Hudson Street Press, $25.95). "Oxytocin is a hormone that is released when women nurse or when you have an orgasm. It also shows up when you volunteer or help others.
"Also, research shows that when you volunteer, there is an increase in your brain activity," Singer adds. "Executive functioning improves. Your stress levels go down, and you can have improved cognitive abilities."
Even seeing an act of kindness can bring on more acts of kindness.
"When someone witnesses a good deed or an act of greatness, they want to be like that person," says Judy Rodgers, co-author of the book "Something Beyond Greatness: Conversations with a Man of Science & a Woman of God" (HCI Communications, $12.95).
For her book, Rodgers interviewed people who performed heroic acts, such as saving someone's life, and activists who risked everything for a cause.
"Time and time again we found that just seeing someone perform an act of unexpected greatness created a level of awe and elevated moods," Rodgers said. "It made people want to change their lives or go out and volunteer. There is a ripple effect."
But what if you chose to mind your own business?
"Most likely it will haunt you a little bit," said Rodgers. "And the reason is—at some level—we know it's our nature to help others. If you are in a state of fear then you won't take the leap and help. That guilt might grow into disappointment as time passes."
And now that science is behind what many have thought to be a moral issue, perhaps helping others will become an automatic response more often.
"I tell my patients that we are all linked in some way and we should be here to help each other," says Saunders. "I think that deep down the majority of us really are inherently good."