If you've watched a dog wag its tail, then you know that animals have the ability to communicate with their bodies. Given that our earliest ancestors may date back millions of years, and complex verbal human language probably didn't exist until 100,000 years ago, it's a good bet that humans relied upon interpreting one another's body movements, posture and facial expressions long before they had words to express what they were sensing [source: Johansson]. In prehistoric times, the ability to interpret another hunter-gatherer's attitude and intentions from a distance, before the person got within striking range, may have meant the difference between life and death [source: Goman].
That urgency may explain why humans became adept at forming impressions and making snap judgments based on what Tufts University psychology professor Nalini Ambady calls "thin slices" of experience, formed in first few seconds of an encounter. Those thin slices, she believes, are generated in the most primitive area of the brain, the same region where emotional feelings are processed. That may explain why we develop such powerful feelings about someone we have just met, whether that person is a prospective mate or someone trying to sell us a used car [source: Flora].
Researchers say body language is a mix of innate, learned and hybrid movements, postures and expressions. Children are born with the ability to blink and blush, for example, while winking and saluting with a raised hand are learned gestures. Laughing, crying and shrugging are hybrid body language because, while they involve innate movements, we are taught how to connect them to certain situations [source: Grayson].
Just as there are thousands of spoken/written languages throughout the world, the meaning of body language can vary from place to place. In the United States, for example, a smile indicates happiness, while in Asia, it may indicate agreement. And while Americans see eye contact as a gesture of attentiveness or self-assurance, in some Asian and African countries, it's perceived as disrespectful. In Italy, it's common to emphasize one's words by waving the arms, but Japanese speakers avoid doing that because in their country it's been deemed impolite [source: Rugsaken].