AN: This story takes place after the 100th episode, but there isn't necessarily a direct timeline. Though, I did pretend that the last episode never happened as I was writing this. This is un-beta'd, so all grammatical mistakes are my own.

~BB~

Dr. Temperance Brennan is not a woman who does things without thinking. There have been times when she has rushed head first into dangerous situations with only half formed plans, but she'd always thought about the dangers beforehand.

So how, she asked herself, had she come to be in her partner's apartment at quarter past one in the morning on a Saturday, when he wasn't even there?

She had no reason to be there. No reason to be pacing up and down his living room like a trapped animal. But there she was.

She heard the front door open and then close. The lock snaps into place. Heavy footstep.

"Jesus, Bones. What are you doing here?" he says, shocked to see her in his apartment.

She opened to mouth to tell him why she was there, but closes it again. She spends a few seconds taking him in. Noting the rumples in his shirt, the spiked, out of control manner of parts of his hair. The dark, tense look in his eyes.

"Did your date not go well?" she asks.

"Get out of here Bones," he shoots back, walking towards his bedroom.

But she doesn't leave. Instead, she sits on the couch, looking at the room around here. In the corner is his bag of hockey gear, the sticks leaning against the wall. His coffee table has a few magazines, mostly about cars and sports. His apartment is cluttered, much less organized then her own. But, it is distinctly his and that calms her in a way she didn't expect.

His bedroom door opens and he returns dressed in sweatpants and a simple grey t-shirt. He sighs as he passes in front of her. The fridge opens and she hears the tell-tale sound of a bottle of beer being opened, followed by another.

He hands her the second bottle as he sits beside her on the couch. His muscles relax and he allows himself a few moments of controlled breathing to calm his nerves.

"You were right. It didn't go well," he says.

"I'm sorry," she replies.

They both take hard pulls of their beers, each not looking at the other.

"So, why are you here Bones?" he inquires, after a few quiet minutes.

She thinks for a moment. She still doesn't know why she is there, what she was thinking, but she does know that there is something she wants to say to him. But like so much else, she has no idea what it is. So, she tells him what she does know.

"Science tells us that there is a scientific explanation for everything. The planets orbit the sun because of the gravitational field it emits. The earth is 4.5 billion years old and life didn't first occur until nearly a billion years later. Australopithecus afaransis, one of human's earliest ancestors, lived between 3.7 and 2.9 million years ago, in Africa. They are believed to be the first fully bipedal primate. Homo habilis, which lived 2.3 to 1.4 million years ago was the first to use tools. Their brain capacity was 510cm. Modern humans, Homo sapien, appeared only 200,000 years ago in the archaeological record, but Archaic Homo sapiens evolved 500,000 years ago from Homo erectus. There is debate among the anthropological community about whether or not Neanderthals are truly a separate species or are a subspecies of Homo sapien. It is possible that Homo sapiens and Homo neanderthalensis interbred, and that Neanderthal genes survive today in modern populations. This would be impossible if they were truly separate species."

He raised an inquisitive eyebrow, unsure were her thought process was taking here.

"The first human city was Catalhoyuk, 9000 years ago, in what is now modern day Turkey. As time progressed, humanity would settle many different areas and civilizations would rise and fall. Artwork changed styles, pottery changes shapes, and cultural norms just as swiftly. But, the genetic make-up that makes us human has stayed the same. Humans are the same as they were over 100,000 years ago."

She took a breath.

"I am not a cultural anthropologist. I do not study cultural norms and their impact on society because I do not understand them. They are always changing and trying to figure them out is as reliable as trying to predict how hot my coffee will be if I reheat it in the crappy microwave at the FBI. I became a forensic anthropologist because it is predictable. It is stable. Human bones do not change, except for very specific reasons. Scientifically proven reasons."

He started to say something, but she held up her hand in a motion for him to stop.

"I do not do well with change. Change is not stable. Change cannot be predicted, it cannot be understood. And I am afraid of what I do not understand. Biology tells me that what I am feeling is caused by hormones. The release of endorphin by my brain due to the fact that I find you visibly pleasing to look at. But, this does not happen around other pleasing to look at men. Hodgins' is very fit. Andrew is tall and has wide, strong shoulders. But my brain does not release endorphins when they are around. "

This time, she had to physically put her hand over his mouth to keep him from talking.

"But with you, everything is different. My heart speeds up. I feel warm. My body releases tension when you are around. It makes me want to be around you. To touch you. I know there is a biological explanation for everything, but I do not know why. Why it only happens with you."

She took a deep breath and let it out slowly.

"Angela tells me that it is love. That love is what is making my body respond as it is. But I don't know what love is. I can't measure love. It cannot be quantified. Scientifically, it does not exist. But then why do I feel like this? Booth, you're the person I go to when I can't understand something that everyone already knows. I need you to explain this to me."

She let out a breath, somewhere between a sigh and a huff.

"Oh Bones." He took her in his arms, holding her close against his chest.

"I have no better explanation then Angela. But I can tell you that love does exist. Think back to when you were younger, before your parents left. Do you remember a time when you were hurt? Fallen off a swing or a bicycle?"

"I was 10. I was trying to ride Russ' bike, even though it was too large for me. I fell on the driveway and skinned my arm. Dad had to remove the grit before he could bandage it." She said.

"And your arm felt better. Even though your dad did nothing more than clean it up and cover it with a bandage. He used no painkillers, did nothing to dull the ache. I'm betting that he kissed it, told you everything would be fine. And knowing you, you got right back on your brothers bike."

"I fell off again, but this time on a pile of rocks. I broke my left radius."

"And your parents took you to the hospital. They sat with you in the waiting room. They comforted you when the pain hurt too much. Held your hand as the cast was put on. And then they took you home. And that night they put you to bed, and wished you sweet dreams. And you fell asleep, knowing you were safe. That, Bones, is love."

"Booth, that is a parent investing in the health of their offspring." She argued.

"They didn't have to do it Bones. They didn't have to get you the medical care you needed for your arm. They could have let it heal as it was. But they didn't Bones. They didn't because they love you."

She tried to speak, but he placed a single finger on her lips.

"Your father came back to Washington because he loved you, because he wanted to make up for the past. He came back, despite the fact that he was wanted for murder."

"Booth, all your evidence only suggests that parents love their children. It's an evolutionary strategy to ensure the survival of their genes into the next generation."

He sighed. He got up and walked back to his bedroom, returning a moment later with a picture frame in his hand.

He sat down on the coffee table in front of her and handed her the frame.

"What do you see?" He said.

She looked down. It was a picture of two people, and elderly man and woman. She recognized Pops, his grandfather and deduced that the woman was likely his wife, and Booth's grandmother.

"I see your grandfather and your grandmother." She said.

"They married in 1940. My grandmother, she married Pops against her family's wishes. He was poor and the Booth family was considered pariahs, being the unfortunate descendents of John Wilkes Booth. She was from a well-off family and had many prospects. There was no good reason for her to marry him. But she did, and her family disowned her. They lived in poverty until he joined the military and she started working in a factory during the war. Things were better, after that, but they were never more than a simple middle class couple. Open the frame."

She did as he said, sliding the metal hooks holding the back in place. There was an older photo hidden behind the one she saw. She lifted it out gently, taking care of the worn edges.

It was a young couple, staring at each other. The man was in a suit and the woman a white dress. She could see the physical markers identifying the man as Hank Booth. It was him and his bride at their wedding.

"They look happy." She said quietly.

"They were in love." He replied, "They didn't marry for money. Or because they could provide resources for each other. They married because they loved each other. Because they wanted to spend the rest of their lives together, no matter what. They sacrificed all they had to be together."

She was silent, staring at the picture and trying to understand the story just told to her. But for all her intelligence and despite her three doctorates, she could not come up with an anthropological reason as to why these two people would marry.

He took the picture and frame from her hands and set them aside. He grasped her hands in his own, holding them tightly.

"That is what it means to love, Bones. It means you want to spend the rest of your life with someone, no matter the consequences. That they are the first person you want to see in the morning and the last person you want to see at night. It doesn't matter if they are rich or poor or if they are good breeding material or not. All that matters are the emotions and the bonds between those two people."

She was silent again. She concentrated on the warmth his hands were providing hers. His touch was soothing and yet, at the same time, causing her heart to pick up speed.

"I don't know how to love." She whispered.

He moved his hands from hers and instead grasped her face. He looked into her eyes.

"Yes you do. You love Angela and Hodgins, Zach and all your goofy interns. You love your father and brother, despite all the pain they have caused. It's not the same type of love as between two intimate people, but it is love none the less. Being in love with someone, it's just stronger then the everyday love between friends and family. It can be more complicated, since there are physical and sexual factors involved, be it isn't that much different."

She covered his hands in her own.

"That night, after we talked to Sweets, you said you loved me. Everything you said to me, it's what you've been feeling?"

"Yes, it is. I'm in love with you. I can't imagine my life without you in it. I want to spend the rest of my life talking, bickering, and chasing down bad guys with you. I want to see you every morning and every night. I want to cook you breakfast when you're tired; rub your feet after a long day at work. I dream about kissing you, about making love to you. Every aspect of my life, I want you in it."

She was crying by the end of his confession. He whipped away a tear with his thumb, stroking her wet skin. He moved from his perch on the coffee table and once again sat with her on the couch. But his time he wrapped his arms around her, pulling her close.

"That's what love is then?" she said into his chest.

"Yeah, Bones, that's what love is. And I'll spend every day of my life proving it to you, if you'll give me the chance."

"Ok, because I think I love you too."

~fin~

AN: I did my best to emulate how I believe Bones' thought process might proceed when trying to understand the concept of love. To my knowledge, everything she states scientifically is correct. Yay for Anthropology classes and Google.

Like all authors, I love feedback from readers. So please, leave me a review!