Romantic love is as ancient as time itself, and it has long been considered the province of philosophers and poets. After all, it causes waves of euphoria and torment that seem to come crashing down at the slightest provocation, defying all reason or logic.

It tends to manifest just at the moment we aren’t looking for it, and often, the person with whom we are falling in love makes very little sense to our friends and relatives.

Still, like so many other elements of the universe that once seemed random and mysterious, science has recently given us a great deal of insight into the process of falling in love. Here are the stages you're likely to experience, as well as the signs you're in love.

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1. Inception

Inception is the moment at which a certain someone begins to take on a whole new meaning in your life. It might be someone you have known for years or someone you met just hours ago.

Either way, you begin to focus intently on that person, a trait known as salience to scientists. Congratulations. Whether you meant to or not, you have begun the process of falling in love.

2. Intrusive thinking

The next step occurs when thoughts of your love begin to intrude into your mind. You replay snippets of conversation, recall exactly what he was wearing one night, or think fondly of her smile.

You wonder what he would think of the book you are reading, or what her advice on your problem with your boss might be. Every meeting with your beloved, whether planned or happenstance, becomes a weighty event worthy of ongoing review.

In the beginning, these intrusive thoughts come only occasionally. As you move further into this stage, though, they become obsessive. In fact, people tend to spend 85 to 100 percent of their time thinking of the person with whom they are falling in love.

In most cases, real life goes on as normal, with the thoughts forming a pleasant backdrop to the tasks of daily living. Sometimes, though, people in this stage become distracted and have trouble focusing on work or school.

3. Crystallization

Those in love are sometimes said to idealize their beloved, but science shows that this is incorrect. Instead, the third stage of falling in love is known as crystallization. This is when you begin to develop a clear picture of not only your love’s strengths, but also his faults.

Rather than an ethereal figure, your beloved is becoming a whole, real person in your mind. Still, despite knowing her faults, there is a tendency to dismiss them or even view as them as charming quirks.

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4. Craving, hope, and uncertainty

Craving, hope, and uncertainty go hand in hand with crystallization. Now that you have a clear picture of who your beloved is, you are overcome with the desire for a relationship.

Everything that happens between you becomes fraught with emotional meaning — the slightest positive overture becomes proof that your love is returned, while the tiniest rebuff becomes grounds for despair. Separation anxiety and the determination to overcome any obstacles to your love are part of this phase.

5. Hypomania

At some point, you will likely start to experience what scientists refer to as hypomania. This is the rush of energy that makes it feel like you need little food or sleep.

However, it also tends to come out in such nervous reactions as flushing, trembling, physical awkwardness, stuttering, sweating, and a racing or pounding heartbeat.

6. Jealousy and intense motivation

Those who have advanced down the path of falling in love tend to experience a strong motivation to win over their love interest. Irrational jealousy and behaviors known as mate guarding, designed to warn other potential partners away from your beloved, are common.

The fear of rejection and an overwhelming sense of longing also tend to appear at this time.

7. Helplessness

At some point, your intense feelings will likely give way to a sense of helplessness. You may at first feel despondent, but as the obsessiveness starts to subside, you might wonder why you ever behaved so irrationally.

At this point, you may still very much want a relationship, but you begin to resign yourself to the notion that what will be will be. Pragmatism and logic gradually take the reins.

Interestingly, though it is true that we are more likely to fall in love with those whom we find physically attractive, sex seems to play only a very minor role in falling in love.

While it is true that people want to have sex with their beloved, they have a far deeper craving for an emotional union. Calling, writing, and spending time together are at the top of the wish list.

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The Anatomy Of Love is Lucy Brown, PhD and Helen Fisher PhD. The neuroscientist and biological anthropologist are best friends and scientific collaborators.

This article was originally published at Anatomy Of Love. Reprinted with permission from the author.