1. Famous poets and writers have claimed for centuries that love stems from powerful emotions. 2.
However, research has shown that feelings of love are at least in part influenced by various
chemicals in the brain. 3. One group of chemicals that is just beginning to be understood is the
pheromones-substances that promote sexual attraction in the opposite sex. 4. Experiments show
that males release a chemical in their sweat that has been shown to be highly appealing to women-
particularly during ovulation. 5. Similarly, women produce their own pheromones that draw men's
interest-one actually can raise the level of testosterone in a man's bloodstream. 6. In addition to
pheromones, another chemical, phenylethylamine (PEA), plays a crucial role in helping people fall"in
love." 7. Related closely to the addictive stimulant drugs called amphetamines, PEA actually causes
people to feel a high from their relationship. 8. The "heart-throbbing" sensations new lovers describe
and the feelings of excitement and infatuation that are part of new relationships are directly
attributed to this chemical. 9. As with many addictive drugs, eventually the body builds up a
tolerance to PEA and the strong feelings begin to wear off, usually within two years. 10. This
explains why infatuation cannot last forever. 11. A third group of chemicals-endorphins-appears to
be at work in long-term relationships. 12. Endorphins are the body's natural pain relievers. 13. In
addition, they produce a sense of security, tranquility, and calm. 14. During physical intimacy,
endorphins are released into the bloodstream, creating the feeling of satisfaction and security
common to long-term successful relationships.

The main idea of the above selection is: