Emotional intelligence (EQ) is one of the most important skills candidates need when they’re looking to land a job. And it’s also a key factor to move up the ranks more quickly. We’ve also heard that EQ is a better predictor of success in the workplace than IQ, and that’s been backed by numerous studies in both academia and through data from companies on their employees.

But it wasn’t always part of workplace parlance, essentially because executive leadership often finds it difficult to tie such a squishy concept to productivity, revenue, and other key performance metrics. (Other research does just that, though). So where did this concept originate, and how has it evolved?

EQ’s more than 2,000-year-old origin

Psychologists, scholars, and philosophers have been studying human intelligence throughout history. As far back as Plato in ancient Greece, on through Spinoza, Descartes, Hobbes, and Hume, great thinkers have posited that emotion as a response to certain sorts of events of concern to a subject set off changes in the body that in turn motivate behavior. Over the past 80 years or so, several have introduced theories and language around the kind of intelligence that isn’t gained through book learning.

For example, in a compilation for Tallinn University in Estonia, Sirje Virkus outlines the iterations of emotional intelligence beginning in the 1930s when Edward Thorndike discussed “social intelligence,” or the ability to get along with other people. David Wechsler built on this concept by suggesting that the moods, feelings, and attitudes surrounding intelligence could be critical components to success in life. In the 1950s, Abraham Maslow (yes, the same one who created the hierarchy of needs) discussed how people could develop emotional strength. Twenty-five years later, Howard Gardner published The Shattered Mind, which introduced the concept of multiple intelligences.

Coining the phrase and popularizing the concept

In the summer of 1987, two professors, Peter Salovey (the current president of Yale University) and his colleague John Mayer, were painting the walls of Salovey’s house. The idea of emotional intelligence didn’t exist yet, but the professors were a fortuitous match: Salovey studied emotions and behavior, and Mayer studied the link between emotions and thought. The two had a conversation while painting, and the name “emotional intelligence” was born.

Related: 7 Reasons why emotional intelligence is one of the fastest-growing job skills

According to the history of the development of the Yale Center for Emotional Intelligence, they opined that existing theories of intelligence had no place for emotions.