Do you ever wonder why opposites sometimes attract? And how other times it’s the similarities people share that lead them to together romantically? Biological anthropologist, sex researcher, and chief scientific advisor to Match.com Helen Fisher, PhD, has a theory about this descrepancy in attraction, specifically why some people prefer to find balance with an opposing personality while others subscribe to the notion of birds of a feather flock together.

According to her her typology, which she outlines in her book Why Him? Why Her? How to Find and Keep Lasting Love, there are four broad personalities that are determined by four different neurotransmitters in the brain. (You can take the Helen Fisher personality test for free here! Estimates say more than 14 million people already have.) One of those four chemicals has a dominant footprint in each person’s basic personality and then becomes the basis for whom we’re most compatible with.

Below, find a breakdown of the four different personality types. Knowing yours may help you determine whether your best match is someone just like you or someone who’s your opposite.

Explorer (dopamine): like attracts like

Explorers are the doers, and they’re powered by dopamine (a neurotransmitter involved in pleasure-seeking and motivation). Explorers seek novelty and excitement, and love to learn, travel, and meet new people. They are highly curious, goal-oriented, and value their independence. They live in the moment and typically have a ton of energy. Explorers are often attracted to those who similar-minded. They contend that if you want to do, learn, seek, and experience, you wouldn’t do well with someone who didn’t share those desires.

Builder (serotonin): like attracts like

Builders are the traditional, loyal, balanced types, powered by serotonin (the calming hormone). These people are very routine-oriented and highly planned, valuing authority, rules, and precision. They are typically grounded and fact-based, conscientious and cautious. Builders want to do a thorough job, and they want to do it right the first time. They revere home and family and have a sense of what they “should” be doing at all times. Builders are often attracted to those like themselves, preferring to start relationships and families with others who value peace and tradition.

Director (testosterone): opposites attract

Directors are powered by testosterone. They are analytical and logical, direct and forthcoming. They are sure of themselves, independent, decisive, and skeptical. Directors are resourceful, competitive, and type A, often making excellent leaders. These types tend to be drawn to estrogen-oriented Negotiators, their opposites; the complementary match provides a perfect pairing for the emotionality and people skills that Directors lack.

Negotiator (estrogen): opposites attract

Negotiators are characterized by estrogen. They’re intuitive, charming, insightful, and caring. They do well with ambiguity, and can read between the lines. Negotiators are highly empathetic, and are skilled at organizing and connecting people. They like when everyone gets along, and they are also emotionally expressive. These types are often drawn to testosterone-led Directors, their opposites; Directors can lend the logic, directness, and decisiveness skills that Negotiators often lack.

Evidence you can trust the Helen Fisher personality test

Many people have played with personality science and theory, including the father of it all, psychologist Carl Jung, who came up with the theory of “psychological types.” Myers-Briggs creators Isabel Briggs Myers and Katherine Cook Briggs took Jung’s work and identified 16 unique personalities. From there, David Keirsey grouped the 16 personalities into four basic types: Guardians, Artisans, Rationals, and Idealists.

Though Dr. Fisher claims to have not known about Keirsey’s work prior to outlining her four basic personality types, his classifications of the Myers-Briggs types map onto her breakdown quite closely: Explorers, the dopamine group, resemble the novelty-loving Artisans. Builders, with ample serotonin, share similar traits to the ultra-traditional Guardians. Testosterone-centered Directors are analytical and logical, just like the Rationalists. And estrogen-dominant Negotiators are emotionally-savvy and agreeable, just like the Idealists (NFs).

So, if you’ve ever wondered whether there’s proof of innate patterns in personality, allow the striking similarities between two separate researchers’ ideas to sway your thoughts.

Other personality test intel: Here’s what to know about the Enneagram, and how knowing your type can also help your find a romantic partner.