Secretin
Secretin was the first hormone to be identified. In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion. It was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. They discovered (by cutting all the nerves to the pancreas in their experimental animals) that this process was not, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion "secretin". Secretin was the first such "chemical messenger" identified. This type of substance is now called a hormone, a term coined by Bayliss in 1905.
Motivation
Another basic drive is the sexual drive which like food motivates us because it is essential to our survival. The desire for sex is wired deep into the brain of all human beings as glands secrete hormones that travel through the blood to the brain and stimulates the onset of sexual desire. The hormone involved in the initial onset of sexual desire is called Dehydroepiandrosterone (DHEA). The hormonal basis of both men and women's sex drives is testosterone. Men naturally have more testosterone than women do and so are more likely than women to think about sex.