The Coolidge Effect: What Your Body Notices Before You Do

The story of US President Calvin Coolidge is often retold as a clever joke, eventually becoming a staple in endocrinology discussions regarding a curious biological phenomenon.

During a tour of a farm, a guide wanted to impress the president's wife. He explained that a local rooster was capable of mating dozens of times a day. She smiled and asked him to share this with her husband. When the words reached Coolidge, he asked one question:

Does he do it with the same hen every time?

No, with different ones each time.

Then please tell that to my wife.

The anecdote has long outlived its time, but the name it gave to this scientific phenomenon remains. Later, researchers began testing this idea not on farms, but in laboratories.

Initial experiments were conducted on animals, and the pattern repeated consistently. While a male interacted with a familiar female, his hormone levels remained relatively stable. However, as soon as a new partner was introduced, testosterone levels noticeably increased. Similar patterns have since been cautiously studied in humans.

The most interesting aspect is this: it turned out to be less about the act itself and more about the anticipation.

Why Novelty Captures the Brain

When discussing the Coolidge Effect, it is easy to assume the story boils down strictly to sexual desire. In practice, it is somewhat more complex.

The first system to activate is linked to motivation and the pursuit of new experiences. Excitement emerges, focus intensifies, and curiosity awakens. Dopamine plays a vital role in this chain, and shifts in testosterone levels become part of the body's overall response.

From an evolutionary perspective, this is not surprising. The brain treats familiar situations as solved problems. Novelty is a different matter. Here, the outcome is unknown, meaning the body requires additional resources: energy, concentration, and a readiness to act.

A similar reaction occurs in other contexts. Before a competition, challenging negotiations, or a public speaking engagement, hormone levels can also shift. In all these cases, there is a common element: uncertainty.

Perhaps this is why even the warmest relationships can feel different over time. It is not necessarily because feelings have weakened, but because the brain has stopped perceiving the situation as a new challenge.

The Role of Personal Success

There is another aspect that is discussed far less frequently.

Research by Mazur and Booth showed that testosterone is linked not just to novelty, but to the experience of personal status. This does not strictly refer to work, sports, or competition.

When a person feels mutual attraction or realizes they have successfully piqued someone’s interest or made a positive impression, the body responds. To the brain, such a situation largely resembles a small victory.

Therefore, the presence of an attractive partner is not merely a matter of aesthetics. Sometimes the body begins to react before a person has even had time to process their own emotions.

When Relationships Are Just Beginning

There is another study whose results have long been discussed by experts.

Italian researchers Donatella Marazziti and Giuseppe Canale discovered that at the start of a relationship, hormone levels change for both partners, though they do so in different ways.

In men, testosterone levels typically decrease slightly in the first few months. In women, they conversely rise slightly. Over time, these differences become less pronounced, as if the organisms are gradually adapting to one another.

Romantics might call this the chemistry of attraction, while physiologists prefer to speak of hormonal adaptation. In essence, both descriptions refer to the same process.

This does not imply that every new encounter automatically triggers a surge of hormones or that stable relationships inevitably lose their appeal. Rather, the research shows that the body is highly sensitive to novelty and uncertainty.

Therefore, the slight flutter of nerves before a first date, a sudden burst of energy, or a feeling of inner elevation is likely not accidental. In many cases, these are reflections of very real physiological processes.

Stability provides a sense of security and closeness. Novelty is a different experience, tied to anticipation and the interest of discovery. It seems the body distinguishes between these states much faster than we can consciously process them.