Sexual Dimorphism

Dr. Piper Wingate and Dr. Ben Valentine were part of the initial human expedition to the planet of Perwithia. As xenobiologists their job was to act as liaisons to the Perwithi scholars, learning about their biology and culture, and in return also teaching them about human biology and culture.

It was a difficult task because Perwithia was very different from Earth. The Perwithi were asexual; they reproduced by budding. The Perwithi had a hard time understanding that men and women were both human, and not two separate species.

Dr. Wingate once spent a very frustrating afternoon trying to explain the concept of sex to Professor Xu, her Perwithi counterpart.

"I don't understand," Xu had said to her. "You and Dr. Valentine are so different from each other! Ben is much taller than you, and your body proportions are completely different. I find it hard to believe that you're both human."

"Not only are we both human," Dr. Wingate said. "But men and women--as the two varieties are called--are essential to our survival as a species."

Xu rubbed their cranium with their grippers, clearly straining to understand.

"How so?" Xu asked.

"Let me start by explaining the basics of human reproduction," Dr. Wingate said. "I'm what's called a 'female' and Dr. Valentine is what's called a 'male'. The human contact team contains a mix of males and females. For example, Captain Stark who you've met, is a female like me, and Commander Ramsey, the head of security, is a male like Dr. Valentine.

"Mating between males and females involves merging genetic material from both individuals to create a new genetic code for their offspring. The mating process consists of a sequence of instinctual courtship behaviors that culminate with the male inserting his reproductive organ in a special cavity in the female's body, and squirting his genetic material inside her.

"It all sounds very haphazard and messy," Xu said. "it's hard to believe the survival of your species depends upon such a complicated process.

"I think I'm starting to grasp the essentials," Professor Xu said. "I wonder if it would be possible to arrange a demonstration."

"You ... uh... want to watch a man and a woman breeding?" Dr. Wingate said.

Xu nodded. "If such a thing would be possible ... yes. Purely in the interest of science."

"I might be able to arrange something," Dr. Wingate said. "Captain Stark would have to authorize it, of course."

The next day when Dr. Wingate floated the idea to her commanding officer, Captain Stark was aghast.

"So, they want to watch us fuck, do they?"

Dr. Wingate didn't allow herself to be cowed.

"It's not Professor Xu's fault. They didn't realize how improper their request was," she responded. That's kind of the point. There's so much that the Perwithi don't understand about us. They don't even know what we might consider taboo. Putting on a demonstration like this would go a long way toward building the sort of long-term understanding between our species that will make coexistence possible."

"Ok, you've convinced me," the captain said. "But keep it discreet, ok. If word of this gets back to fleet, Admiral Morgan will have my head!

"The only question now, is who?"

"I was thinking the woman would be me, of course," Dr. Wingate said. "It only seems fair since I'm the one advocating for it."

"And the man ...?" Captain Stark asked.

"I think Ben Valentine would do it. The Perwithi already know him and ... ahem ... he's not bad looking."

"Good choice," the captain said. "From what I know of Dr. Valentine's reputation among the female members of my crew, he's certainly capable in that regard. And apparently rather generously endowed. The two of you should put on a good show. And do humanity proud."

"I'll make the arrangements with Professor Xu," Dr. Wingate said. "And keep it hush-hush."

A few days later, Dr. Wingate and Dr. Valentine met Professor Xu as arranged in the common room. The two xenobiologists looked at each other sheepishly, a little embarrassed by what they knew was coming.

"We probably should have tried a dry run," Dr. Wingate thought ruefully. "What will we do if we don't hit it off? I guess in that case, we'll just have to trust our instincts."

It was only a short walk from the common room to the auditorium.

Professor Xu led them in.

The auditorium was a large domed room with tiers of concentric platforms surrounding a flat circular space in the middle. The platforms were crowded with at least a hundred Perwithi. They were all chattering excitedly among themselves, but they quickly fell silent as the two humans came into view. Dr. Wingate recognized a handful of faces from the contact team, but most of the crowd was unfamiliar to her. Xu had mentioned they were assembling researchers from all over the western continent, but Dr. Wingate hadn't expected there to be quite so many of them. She felt a sudden flutter of butterflies in her stomach. It was a little late in the game to have an attack of modesty, wasn't it? Twelve or two hundred, what did it matter?

The Perwithi had laid out a pallet just as she'd requested. Several thick sleeping mats had been pushed together in the middle of the circular floor and covered with a smooth sheet of white fabric. Several days earlier she'd explained to Professor Xu that the human reproductive act often required the participants to be lying down, and clearly, the professor had paid close attention. Half a dozen small pillows were scattered on top of the pallet, and a jug of water with two drinking bowls had been placed nearby.

There were also cameras. Three film recorders were arranged around the perimeter of the circle, their large lenses aimed directly at the pallet to capture the details of the breeding demonstration from every angle. In addition, two Perwithi scribes with hand-held still-image devices stood waiting off to one side. This was clearly a once-in-a-lifetime opportunity for the Perwithi scientists. Forget about having a few hundred spectators--the recordings of the two humans having sex would undoubtedly be analyzed frame-by-frame for years or even decades to come.

No pressure, Dr. Wingate thought.

Xu raised two grippers to gain the crowd's attention.

"Please welcome our kind visitors. The smaller human is Dr. Wingate, who many of you have already read about in the reports from the contact team, while the larger human is Dr. Valentine, one of Dr. Wingate's colleagues who has generously volunteered to assist us with this demonstration."

Dr. Wingate stepped forward. "Thank you for your generous greeting. Dr. Valentine and I are both pleased to be here. The openness and honesty with which your people have greeted us as guests from another world has been truly remarkable. And it is in the spirit of that openness and honesty that the two of us have consented to this demonstration today."

The audience hummed and waved their grippers.

Dr. Wingate continued. "Among humans," she said. "Breeding is considered to be an intensely private act. As you've probably noticed, we have strong cultural prohibitions against even displaying our unclothed bodies in public. The full mating sequence usually only occurs in complete privacy."

A murmur travelled through the audience in response to the novelty of what she was telling them.

"So, I hope you appreciate that in conducting a public demonstration of human reproductive behavior, both Dr. Valentine and I will be violating a number of taboos. We have agreed to do so in the interests of a free exchange of knowledge. However, we hope you realize that performing these acts in front of others will not be easy for us."

"What's going on?" Ben whispered in English. Unlike Dr. Wingate, he didn't speak Perwithi.

"I'm just explaining that humans don't normally fuck in public," she whispered back. "And that they should consider themselves damn lucky that you and I are willing to put on a show for their benefit."

Ben stifled a laugh as Dr. Wingate turned back to the audience.

"Before we begin, I should give a brief overview what you're about to witness. Briefly, the whole point of sexual reproduction is for the male--that's Dr. Valentine here--to insert his breeding appendage into the reproductive cavity of the female--that's me. Afterwards there will be an interval of rhythmic thrusting. The stimulation produced by this thrusting will cause the male to release a fluid containing his genetic material into the female's reproductive cavity. If everything works as intended, one of the male reproductive cells in the fluid will combine with one of the female reproductive cells inside the female's body. This will create an offspring, which the female will nurture within her breeding cavity for about 150 Perwithi days until it becomes strong enough to survive on its own."

There was a question from the audience. An older Perwithi scientist named Trimpha raised a gripper, and cocked their head in an interrogatory posture.

"Will a new offspring be created inside your body today, Dr. Wingate?"

Dr. Wingate shook her head.

"Today's mating demonstration will NOT result in the creation of a child. Humans have developed chemicals to control our reproduction, and I'm currently under the influence of one such drug that suppresses my fertility. So, while Dr. Valentine and I will perform all the steps of the reproductive act, when he squirts his seed inside my body, a child will not be created."

"What did they just ask?" Ben whispered.

"If you were going to get me pregnant."

"What did you tell her?"

"That I'm on the pill, so you won't be knocking me up today."

"I was wondering about that myself ...."

"Shouldn't you have mentioned your concerns earlier?"

"Well, I figured you knew what you were doing ...."

"Be quiet. And start getting undressed."

"Yes ma'am."

Ben began unbuttoning his tunic. As he started shedding his clothes, Dr. Wingate was pleased to note that he had a very nice torso--trim and well-muscled with a cute little patch of dark hair right between his pecs. There was another little line of dark hair on his tummy, running straight down from his bellybutton and disappearing intriguingly into his pants.

Dr. Wingate continued to address the audience.

"Even in our uniforms it should have been obvious that there are clear morphological differences between males and females. As you can see, males are generally larger and more muscular than females, with broader shoulders, and narrower hips and more body hair. Females tend to be smaller and more slightly built than males, with less body hair and higher-pitched voices. There are other structural differences as well, which will become more apparent as we both disrobe."

She paused to allow Ben to take off the rest of his clothes. The male xenobiologist kicked off his boots and then started unbuttoning his pants. Underneath, he was wearing a simple pair of black briefs. He glanced around nervously, clearly uncomfortable to be standing in front of an audience in nothing but his underwear.

Then came the moment of truth. Hooking his thumbs in the waistband of his briefs, he pulled them down, letting them drop around his ankles.

Dr. Wingate raised her hand to her mouth.

"Oh my," she said softly.

Captain Stark had been telling the truth. Ben Valentine was well-endowed.

His cock hung straight and thick along the inside of his muscular thigh. He was uncut, which Dr. Wingate approved of. If the aliens were only going to see one human male, at least they were seeing one in his natural condition.

She gestured toward Ben. "Now that Dr. Valentine has undressed, we can clearly see his breeding appendage. It's that fleshy tube hanging down between his legs. Also of interest are his gonads, which are the glands that secrete the fertilizing seed. Ben's gonads are the large ovoid objects you can see suspended in the pouch behind Ben's breeding appendage. For obvious reasons, they colloquially are known as 'balls'.

"I'll let you in on a little secret: A male human's balls are the most sensitive part of his anatomy. If you ever need to incapacitate a human male, a sharp blow to his balls will usually do the trick.

"That trick won't work on human females though. We carry our gonads safely inside our bodies, not exposed and vulnerable like the males'."

With that comment, Dr. Wingate started taking off her uniform. She unbuttoned her high-collared tunic, and slipped it off her shoulders. Underneath, she was wearing a simple cotton bra. She could feel Ben's eyes on her. It had been a long time since she had undressed for a man, and she suddenly felt shy.

She reached behind her back and unhooked her bra, letting it fall off her shoulders.

Dr. Wingate's tits were bare. She didn't have big breasts--only about a handful, but her dark nipples were quite rudely erect, standing straight up and begging for attention.

She slipped off her boots, and then pulled off her uniform pants, dropping her panties at the same time.

Naked. She was completely naked. Dr. Wingate had a slim athletic body, with narrow waist and a cute pert little butt. Her pale skin was smooth and hairless except for an extravagant patch of dark pubic hair between her legs. She absent-mindedly ran her fingers through it, fluffing it up from where it had been compressed by her panties.

The audience wasn't paying attention to her though. They were totally focused on Ben and the dramatic transformation he was undergoing. As soon as he had seen his female colleague without her panties, his cock had started to rise. He was now almost fully erect, his cock jutting straight out in front of him and bobbing up and down with each heartbeat.

Dr. Wingate felt she had to comment on what had just happened. She approached Ben and gingerly took his erection into her hand. It was impressively heavy and thick, and the skin was so tender and smooth.

"Dr. Valentine's breeding appendage has started preparing for the mating act," she said. "This was not consciously willed on his part, but purely an autonomous response in reaction to seeing the body of a naked female, namely me.

"I myself am experiencing a similar autonomous response, albeit not as dramatic as Ben's. The breeding cavity between my legs has begun producing lubrication in anticipation of Dr. Valentine inserting his breeding appendage into me."

"What are you telling them?" Ben whispered.

"That your hard-on is making me wet."

"You look so fucking sexy," Ben said. "Piper, I had no idea you were so hot!"

Dr, Wingate was stroking the male xenobiologist's cock. Each time she tugged, she retracted his foreskin, exposing the shiny purple head.

"I promised we would show them courtship behaviors," Dr. Wingate said to her partner. "I wonder if this counts as a 'courtship behavior'?"

With that, she dropped to her knees in front of Ben, and extended her little pink little tongue and licked the head of his cock.

It was such a strange moment. She and Ben had worked together for months, and in all that time as colleagues, she had never imagined that one day she would be down on her knees giving him a blow job. Strange, but not unpleasant.

He really did have a very pretty cock. It fit quite nicely into her mouth. As she sucked him, he ran his fingers through her hair. She looked up at him with her big green eyes and cupped his balls with her left hand. Mindful of what she'd told the Perwithi about how sensitive testicles were, she teased them lightly with her fingernails.

With her right hand she reached down between her legs and touched her pussy. She really was amazingly wet. Her inner lips were all slick and slippery and she actually was dripping onto the mat underneath her.

She felt a perverse pride in knowing that Ben thought she was sexy.

She ran her tongue along the side of his cock, enjoying the reaction it provoked. His hips gave a little jerk forward, thrusting his thick meat deeper into her warm wet mouth.

"Holy shit, Piper," Ben groaned. "I really need to fuck you soon. I can't hold out much longer."

"Absolutely,' Dr. Wingate said, taking his dick out of her mouth. "How do you want me?"

"On all fours," Ben said. "So I can look at your sweet ass."

Dr. Wingate dropped down on the mat, and assumed the position. She leaned forward onto her forearms, lowered her head, and raised her rump in the air, presenting herself to her partner.

She could hear the camera shutters clicking, and the lenses of the film recorders zoomed in to capture every detail. The audience was paying close attention. Many of the scholars in the room had personally worked with Dr. Wingate and it was shocking to see her like this--naked and aroused and down on her hands and knees waiting to be bred. A low hum of conversation filled the auditorium as the audience discussed the strange alien ritual playing out before them.

Ben dropped down on all fours as well and crawled over to her. He stuck his face into her upraised ass and started eagerly licking her pussy.

"When a human female is aroused," Dr. Wingate explained. "Her body exudes a variety of chemical cues that accelerate the mating response in the human male.

"Now that Dr. Valentine has smelled and tasted me, it's unlikely he will be able to resist mounting me for much longer."

Indeed, it was true. Ben took his cock in his hand and rubbed the head between Dr. Wingate's pussy lips, opening her up. Then, growling slightly, he eased his hips forward and penetrated her. The audience could see everything--his thick meaty shaft sliding into Dr. Wingate's body and Dr. Wingate herself reaching back between her legs to help guide it in with her hand. His cock was so large it was hard to believe her small frame would be able to accommodate it.

Dr. Wingate narrated what was going on.

"Dr. Valentine's breeding appendage is now fully inserted in my reproductive cavity. Now he will perform a series of rhythmic thrusts that will culminate in the eventual release of his genetic material inside me ... ohhhh fuck!"

She hadn't meant to cry out, but the Ben's cock felt so good, she couldn't help herself.

His strong hands were on her ass, holding her firmly in place.

She arched her back, pressing back into him, and then he started to thrust.

"Yes, that's it! Give it to me! Give it all to me! Unh ... unh ... unh... unh ... unh!" She grunted in pleasure every time he slammed into her.

He reached underneath her, grabbing her tits, squeezing her thick dark nipples between his fingers, pulling them, stretching them.

Piper's head was spinning. Everyone in the auditorium was watching her, watching her get fucked like a dirty little whore. True, the Perwithi didn't know what a 'whore' was, but Piper knew, and right now she felt like the biggest whore who had ever lived.

She wriggled her ass because she knew Ben would like it. What she really wanted right now was for Ben to pound the shit out of her sticky little whore's cunt. She wanted him to fuck her senseless.

And that's just what was going on. Ben was fucking her hard, driving his big thick cock into he right to the root. His heavy balls were swaying in their hairy sack, his heavy balls that were so full of cum for her whore's cunt. She could tell he was getting close. She was too. It occurred to Dr. Wingate that she hadn't explained to the Perwithi what an orgasm was, and she wondered what the audience would make of what was about to happen.

Piper came first, bucking and shaking as Ben pounded into her. Her pussy clenched tight around Ben's cock, and she let out a long throaty moan. That pushed her partner over the edge and Ben came too, gripping her pelvis tight as his cock throbbed and pumped. He unloaded deep inside her, the hot sticky semen squirting out in a thick gush.