A Lesson in Biology
Copyright© 2026 by Lubrican
Chapter 4
Coming of Age Sex Story: Chapter 4 - She wanted to be a cheerleader but her grades were too low. Summer school might solve that problem. But she needed a tutor to make sure. Her mom got a name from the school and he was hired. When they got to the biology tutoring, she wanted to understand the reproductive system. He was happy to teach her about it.
Caution: This Coming of Age Sex Story contains strong sexual content, including mt/ft mt/Fa Mult Teenagers Consensual Heterosexual Fiction Incest Mother Son Brother Sister Harem Interracial Black Male White Female First Lactation Masturbation Oral Sex Petting Pregnancy Voyeurism
The mood in “the room” was more relaxed than one would expect it to be. Marcus had been answering questions honestly, so when Robin asked him if he masturbated he told the truth.
“Yup,” he said. “And I’ll just admit it here and now. When I do that in the future I’m going to think about your mother ... and you.” He frowned. “I hope that doesn’t make you mad or gross you out. I’m just being truthful.”
“I’m pretty sure I’ll be thinking about you when I masturbate in the future, too,” said Molly. “I don’t think I’ll be able to not think about you.”
“Do all boys look like that?” asked Robin, pointing at Marcus’s groin.
“I’m told I’m a little larger than most guys,” said Marcus, modestly.
Molly let out a harsh hack of a laugh.
“Baby, he’s enormous. I’ve never seen one that big, and before I married your father I saw a few. I feel like I’m reasonable in saying that would scare the shit out of most women who saw it with the impression he was going to try to make love to them with it.”
“I’ve never heard you use that word,” said Robin. Swearing was a big no-no in their family.
“Forgive me. I’m still in shock.”
“Are you scared?”
Molly looked at her daughter.
“No, Sweetheart. I’m not afraid. I’m not afraid of Marcus. I don’t know him well at all, but he’s been around long enough that if he was untrustworthy I would have sensed it by now. I trust him. I don’t think he’ll try to hurt either one of us. If I didn’t think that way I’d make him leave.”
“Good. Because I’m not scared, either.”
“I thought we were going to go skinny dipping,” said Marcus, still looking like he had a flesh dowsing rod attached to his groin.
“The water is right there,” said Molly, who sounded less flabbergasted and more comfortable.
Marcus went to the edge of the pool and executed a smooth, beautiful dive into the water. The only jarring thing about his image was his penis, jutting away from his otherwise streamlined body.
“Are you really okay, Honey?” asked Molly.
Robin nodded.
“I see the bulges guys have all the time at school. All of us girls know what’s making those bulges and now I know why. This is kind of neat.”
“Well, understand that the bulges in the other boys pants are made by something that looks more like Marcus’s middle finger. He’s truly impressive. He makes me feel things I definitely should not feel.”
“Like what?”
“Like your father cheats on me, and in my mind that means I get to break our vow of fidelity, too.”
“You mean have sex with other men?”
“Not men. I don’t want to act like a slut. And I honestly can’t think of any other man I’d think about doing that with.”
“Any other man? Do you mean any other man than ... Marcus?”
“Yes, Sweetheart,” said Molly, whose voice was suddenly shaky again. “Marcus is an alpha male and I can’t help but react to that. That doesn’t mean I’m going to try to have sex with him. I’m like every other woman who’s ever seen that thing. I’m pretty sure you’d have to call an ambulance if he put that in me. Still, I can’t help but wonder what it would be like. I know it’s crazy and I’m probably certifiably insane. I shouldn’t even be swimming naked with him.”
“Technically, you’re not actually swimming naked with him,” said Robin. “He’s in the water and you’re not.”
Molly looked into her daughter’s eyes.
“I need to know how you feel about the fact that I’m thinking about cheating on your father.”
Robin’s gaze didn’t break.
“Mom, he’s an idiot for doing what he’s doing. He’s the one who is certifiably insane for messing up our family like this. So no, I’m not freaked out by the fact that you’re attracted to Marcus.”
“I didn’t say I was attracted to Marcus,” said Molly.
“Well, aren’t you?”
Molly blinked. She frowned.
“I guess I am,” she said. How crazy is that?”
“I think you could do waaay worse,” said Robin. “I like him. I’ve liked him ever since he started tutoring me. Now, seeing him like this and knowing how you feel, if I can figure out what I’m feeling means, I think things will be okay. You want to know something funny?”
“Sure.”
“When he got naked and took his glasses off, I thought of Clark Kent and Superman.”
Molly laughed.
“What you’re probably feeling is in your subconscious. Marcus said it, himself. Evolution has made us women try to seek out the alpha male, because he’s the one who will take care of us and our children. We feel that way even before we have any children. In fact, it’s the alpha male who makes us start thinking about having babies.”
“I’m not ready to have a baby, yet,” said Robin. “But I think I get it. When he took off his shorts I got this tingling feeling behind my belly button and my nipples got itchy. That’s attraction ... right?”
“That’s attraction,” said Molly. “I felt the exact same thing. You and I need to be careful with Marcus from now on. It wouldn’t be smart to give in to those feelings.”
“Yeah,” said Robin. “If you had his baby it would come out brown.”
Molly closed her eyes.
“Yes, that would be crazy,” she said. “Okay. I’m going to get in the pool. You don’t have to if you don’t want to.”
“Okay,” said Robin.
Molly went to the edge of the pool and executed just as beautiful a dive as Marcus had. Marcus was treading water in the deep end of the pool and Molly let her dive carry her most of the way toward him under water. She came up a dozen feel away from him and slowly used a breast stroke to get closer to him.
“Is everybody okay?” he asked. “I didn’t come here to upset anybody or mess things up.”
“Nobody is upset. It doesn’t feel like a mess, yet. Where did you learn to swim? I was a Red Cross Water Safety Instructor in high school and the first year of college. I’m aware that black people don’t have the same composition of the joints and the synovial fluid is a little different. Basically, black people don’t float as easily as other races and many blacks find it difficult to learn to swim.”
“My uncle was in the navy and he didn’t know how to swim. While they were in the middle of the ocean one day he looked at all the water and decided it was pretty stupid to be that way if the ship could go down and leave you in the water. So he learned how to swim. He wanted me to feel comfortable in the water, too, in case I decided to join the navy some day, too.”
“Is that what you’re thinking about doing?”
“No. The military isn’t my style. I’m too resistant to authority. This right here is a good example. The people who think they have authority would tell us what we’re doing is wrong, for a dozen reasons. And my attitude about that is for them to shut the fuck up, pardon my French.”
“I’ve never been rebellious before,” said Molly. “I think you have infected me. I like this a lot and I want those people to mind their own fucking business, too, pardon my German.”
Marcus grinned. Then he got serious.
“I hope this isn’t hurting Robin. You’re an adult and you’ve been in situations like this before, but she has been protected from the world.”
“First of all, I’ve never been skinny dipping with a man, black or otherwise. Nor have I hung around a naked man who had an erection that looked like a battering ram. Third, I’m not too worried about Robin. She wasn’t afraid when she saw you. She’s about to dive into the water and join us, so I don’t think she is stressed out.”
Marcus turned to watch as Robin dove into the water, using the same shallow racing dive that he and Molly had used.
“If anything, she might be a little too curious about you.”
“Are you curious about me, too?” asked Marcus.
Molly continued to use the smooth, easy strokes that kept her afloat and in one spot.
“I’m not sure I want to answer that question,” she said.
“That’s okay. I just want to make sure it’s okay for me to ogle you.”
“It’s fine for you to ogle me. Can I ogle you?”
“Yup. Just understand that if you do, it’s going to stay looking like that.”
“I wouldn’t want it any other way,” she said.
Robin arrived and, with a chipper voice, asked, “What are you guys talking about?”
“We were deciding if it’s okay for us to stare at each other,” said Molly.
“Well, based on my own feelings, I wouldn’t be able to keep from staring, even if it was rude.”
“When people get nude in groups, together, it isn’t rude to stare.”
“Like in a nudist colony?”
“Actually, now that you mention it, I’ve heard that it is rude to stare in a nudist colony,” said Molly.
“Well, I’m going to stare. In fact, I’ll probably stare while you’re dressed.”
Marcus grinned.
“So that means I get to stare at you when you’re dressed.”
“People, let’s calm things down a little. What is happening to us is that our fantasies have been altered. That’s fine, unless that’s all we think about.”
“So what is your fantasy?” asked Robin.
“Still unformed,” Molly lied. “Maybe we can talk about that after Marcus leaves.”
“Are you guys finished talking?”
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