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Biology 103
2003 Second Paper
On Serendip

Sibling rivalry (the slightly-less-amazing adventures of Professor Sanderson's Sociobiology discussion group)

Brittany Pladek

Why yes, it's...

The slightly-less-amazing adventures of Professor Sanderson's Sociobiology discussion group!

Today's topic: Sibling Rivalry


Professor Armand Sanderson's Sociobiology lecture was not quite as popular as his brother Julian's Paleobio class. Partly this was because sociobio did not lend itself to psycho-Permian field trips; partly this was because he, unlike his Cosmopolitan brother, looked more like a lumberjack than a professor. In fact, the highest attendance he'd ever recorded occurred on the day he brought Julian in as a guest. This annoyed him.

"Good morning," he addressed the sea of faces sourly. "As I'm sure you all know, today we have my brother Julian in as a guest." Julian waved cheerily. Fifty-seven eyelids batted. "He's here for today's discussion on the biological origins and implications of sibling rivalry among humans. I expect you all to participate." Despite his gruffness, he received only minimal acknowledgement.

"Julian," he continued, noting with ire the sudden leap in his students' attention, "is here to provide a living example of the concepts we're about to discuss. He's also good with animal behavior, so he'll be starting you off today with some of the biological bases of sibling competition." He narrowed his eyes. "I expect you to pay attention to what he's saying."

The threat was habitual, and, in this case (he again noted with ire) completely unnecessary. The class had no trouble obeying. As Julian stepped forward, all talk immediately ceased---though some of the students' comprehensive faculties ceased along with it.

"Good morning, everybody!" Julian chirped. "Like Armand said, today we're here to discuss sibling rivalry. We don't have a lot of time, so I'll just jump right in. Now, how many of you here have ever fought with your brothers and sisters?" All but a few hands went up. Julian nodded, smiling. "Right. So you would say it's a common problem?" The class murmured agreement. "Well, you're absolutely right. This may come as a surprise to you, but humans aren't the only species who get ticked off by their siblings. In fact, sibling rivalry is ubiquitous in nature. ((5))"

Leaning back, Julian lifted himself to sit on the edge of Armand's desk. Armand, typically, scowled. "For a good example, look at baby pigs," the younger professor explained. "They push each other out of the way so they can get at their mom's anterior teats---that's where the best milk is. ((2)) And baby kestrels will physically fight one another over the food their parents bring back. ((3)) It gets pretty violent sometimes---just like home, right?" A few students chuckled. "Yeah. That's not even the half of it. For example, baby sharks will---this is gross---eat one another in the womb. ((5))" His face crinkled with disgust. Behind him, the elder professor breathed an imperceptible sigh. He had never appreciated his brother's tendency to melodramatize biology.

A hand went up in the back. Julian, abandoning his grimace, motioned the student to speak. "Um," she said uncertainly, "that's gross, but don't they do it for a reason? I mean, I read somewhere that this fits into Darwinism... does it?"

The professor scratched the back of his neck. "Tricky one," he replied. "Me, I say it does... what you're referring to is the theory that sibling competition---if it proves fatal, as in sharks---is actually natural selection because it weeds out the weaker genes from the stronger. The bigger, healthier baby shark will survive to breed. ((1)) However..."

"However," Armand broke in, with a grumble from behind his desk, "That argument falls when you consider that siblings share half their genes. ((1)). Why would you kill off someone who's going to pass on so much of your own genetic material?" He crossed his arms. "Even twins fight, though they're basically the same."

Off to the right, a pair of hands went up simultaneously. They belonged to the class's single set of twins, only one of whom---a darkly dressed but cheery looking goth---was actually enrolled. The other, a bouncy prep, was visiting for less academic reasons. "I take issue with that," the goth said when Armand waved her forward. "Twins may be genetically the same, but that's where it ends." Her sister propped her fists on her hips and added, "Yeah. My sister and I are identical twins, but we're totally different. If we had kids, they wouldn't be exactly alike. I mean, we'd raise them differently and stuff, because of our personalities." The goth nodded approvingly, then picked up, "Who you are isn't just genetic. Who says survival rates have to be dependent solely on genes?"

Armand frowned, looking surprised and a little ruffled. "True," he admitted. "But it's still the genes that determine who your children are. Darwinism still applies. If both of you reproduce, your offspring will have---from your side---the same genetic chances of survival."

A soft, disagreeing cough issued from the front of his desk. "But that depends on how important genetics are. Are they that crucial?" Julian asked quietly. For all his usual placidness, a distant debater's spark had appeared in his eyes. "Not very. Maybe how you're raised is more important. Kids, even twins, compete because they're not the same, despite genetics. No matter what their DNA, they'll still have differing chances of survival." He spread his hands. "Say those baby pigs are all identical twins. They're still individuals, so they still have to compete." Craning back, he flashed a brief grin at his brother. "So Darwinism still applies. It's just not genetic. Behaviors can be passed on, too."

The elder man let out a huff. "Fine," he agreed grudgingly, in a tone which by no means indicated surrender. "Anyway, we're getting off topic. What we're actually supposed to be getting to is why sibling competition occurs." He glanced at his brother. "Julian?"

"Eh, right, right." Julian crossed his legs and leaned back onto the desk. "Although I think we've already sort of addressed it... why do siblings compete? It's more a matter of what they compete over. And the answer can be summed up in one word: *Resources*. ((6))" He slung one arm across his knees, gesturing with the other. "Take baby birds. They fight each other for the biggest share of the food their parents bring home. The bigger chick generally gets more food and has a better shot at survival and, later, reproduction. ((6))" He looked amused, then thumbed a hand back at his brother. "For example, if Armand and I were chicks, he'd be the bigger chick, so he'd probably be the one who'd end up reproducing. Hah, hah."

Armand's eye was twitching. "That is wrong in so many ways I'm not even going to address it. Anyway," he cleared his throat disgruntledly, "now that we know a little about sibling competition in general, we can get on to our specific topic: what's the relation between animal sibling competition and human sibling competition?" He smirked a little as he added, "This is Sociobio, after all."

"But aren't humans animals?" a girl piped up from the recesses of the classroom.

He groaned. "Yes, yes, we'll get to that. Stay on the topic for now."

"Resources!" Julian chirped helpfully.

"Resources," Armand agreed tiredly.

The same girl broke in again, voice sounding slightly peeved. "But we can't talk about resources. Humans don't fight one another for worms like birds do. Our parents treat us equally."

"Ah, but do they?" Julian asked. He glanced back at Armand, who took the cue and continued.

"Look at it in terms of resources," he explained. "Human siblings do compete. They just compete for different resources than birds. Parental time, affection, love, and approval, to name a few. ((5))" He pursed his lips to hide a grin. "For example, Julian and I used to fight over our parents' time..."

"Yeah," Julian reaffirmed, chuckling. "You always wanted them to take us to those idiotic football games."

"And you always wanted to go shopping!" Armand snapped. Reddening, he turned back towards the class. "Eh... don't mind that exchange. The point is that it's these commodities---time, affection---that make for healthier human children. Well-loved children are always more likely to turn out all right. So siblings fight for that resource, just as they do in nature. ((5))."

"There's even a tendency towards birth order discrepancies," added Julian mildly. "You know how in animals the elder sibling is usually bigger and stronger? Well, in humans the older one tends to be more aggressive, perfectionist, blah blah... the younger sibling is easier-going. ((1))" He smiled sunnily. The class, swooning, smiled back. Behind the desk, Armand put his chin in one thick hand and frowned. He was saved from having to defend himself by the twins, who once again raised their hands simultaneously.

"Excuse me, but that's not always true," the prep-twin pointed out. "I know plenty of people whose younger sibling is the more aggressive one." Her sister nodded, myraid black bracelets jingling. She added, "Also, I don't think it's a given that human siblings always fight. My sister is my best friend." The prep sniffed approval, and threw an arm around her sister's shoulders to further illustrate the point.

Armand---surprisingly---responded to the counterpoint with a wide smile. The class lurched. "Finally," Armand ground. "I was wondering when someone would bring that up."

"Um...." Asked the prep twin, "Bring what up?"

"The fact that siblings don't always fight!" the elder teacher rumbled. "I thought that would have been the first thing you'd pointed out. This class is slow today." He tossed a dark look at his brother, who still perched, cross-legged and oblivious, at the edge of his desk. "Are humans animals? Yes. Do they act like animals? That's a more difficult question."

Julian let one leg drop and swung into a more stable position. "You have to remember that everything we're telling you is the result of certain scientists' studies. Just because they seem accurate for one case---say, baby pigs---doesn't mean they're accurate for other cases. Especially humans. We're different."

"Oohhhh." A new voice, high and quiet, drifted from somewhere in the intermediate middle of the room. "Because of consciousness," the student said. "And morality."

"Yes," Armand confirmed. "So the base question is: do humans still follow nature in the way they interact with their siblings? Competition, resources, and cooperation alike?" He scanned the class for hands.

After an awkward pause, one raised tremblingly, and the same high quiet voice began, "I think so." It paused, seemingly unconfident, then continued, "Look at many world societies. First-born children usually inherit the most parental power. They're treasured. Maybe it's because parents feel they're stronger, so they'll survive longer. ((1))"

Before Armand could comment, a different hand shot up. It belonged to an equine girl in the front row, who began talking without waiting for acknowledgement. "Not only that," she whinnied nasally, "but those same societies are famous for their sibling feuds. The story of one sibling opposing the other is ingrained into our culture." Her gaze flashed around the room. "Have any of you ever seen 'The Lion in Winter'?"

The elder professor nodded patiently. "Yes. You have a point about the deep-rootedness about the motif. But it's better displayed elsewhere than in Katharine Hepburn movies."

"Fairy tales, maybe?" Julian offered. "Cinderella's evil stepsisters? Belle's jealous sisters? Both were angry because she was the biological newcomer---yet also the prettiest, the most likely to win the heart of some prince and... um, well, reproduce. That jealousy fueled rivalry which got both princesses in trouble."

"But---" the prep twin blurted, a second before snapping her hand into the air, "You can't just say it's a motif like that. If you're doing fairy tales, look at Hansel and Gretel. They actually protected one another. No rivalry there." She blushed, obviously uncomfortable with directly disagreeing with Julian.

He shrugged obliviously. "Point taken," he admitted. "This is a hard question."

Armand looked towards the nasally girl. "And just because it's ingrained in our culture doesn't mean it reflects reality. If so, then unicorns and dragons would exist. What you want is biological evidence that human sibling rivalry is---well, biological. For example, the fact that siblings are different..." He inclined a shoulder at Julian. "... may show that they're using differing adaptations to get 'resources' like love and attention from their families ((1), (5))."

Julian had caught the movement, and returned it with a broad hand sweep. "To put this into more specific context," he extrapolated, smiling mischievously, "Look at Armand and me. He adapted all this brawny star-football-player-ness to demand attention and praise from our parents. And he adapted this standoffish Ivy League IQ that ensured they'd put him into graduate school." Armand's scowl deepened as his brother's grin broadened. "So I adapted the other way. I'm the cute one, the conciliatory one, that mum and dad liked to spoil. We both get what we want---he by showing off, me by looking cute." Feminine sighs and murmuring agreement from around the room enthusiastically confirmed his self-description.

"No, you learned how to whine," Armand retorted. He caught Julian's eyes. "Can we keep this impersonal, please?"

"Aw," Julian pouted. He held up a finger. "In one second." He finished hurriedly, "So you see, Armand and I are just like competing species. We find specific environmental 'niches' and we exploit them. In this case, the 'niches' are just sibling roles in our family structure. ((1)) Sibling rivalry, then, may mimic species competition on a broader scale..." he trailed off at another warning look from his brother.

A disappointed sigh emanated from the class, many of whom found their two professors' rivalry as interesting (if not more interesting) than the topic of rivalry itself.

The gothic twin, however, simply sighed and dutifully raised her hand. "Sorry to be devil's advocate here, but all of that didn't really answer my sister's question," she complained. "Some siblings don't compete. They're friends. And some of them are really protective of one another. Is that not biological?"

"Biological? Not sure," Armand grumbled, rubbing his temples. "Julian, is there animal precedent for that?"

Julian blinked. "Actually, yeah. Excuse the randomness, but in the Taiwanese aphid, each sibling pair has one sterile sibling and one fertile sibling. The stronger sterile sibling protects the weaker fertile sibling from predators, allowing it to reproduce. ((1)) And that's just one of many cooperating sibling pairs in nature."

The gothic twin blinked right back at him. "So you're saying that human siblings protect one another so that they can pass on the family genes?"

"Goodness, no," Julian returned, shaking his head. "I thought we agreed earlier that genes weren't the only important factor in natural selection. And that humans are different because of their morals. I was just saying that sibling cooperation isn't unheard of in nature as a whole." He, too, lifted a hand to rub at his temples, and for a moment the relationship between the two professors was blindingly apparent.

The twin pressed, "So then sibling cooperation in humans isn't biological?"

Armand sighed. "That is what we don't know, and it's basically the heart of today's discussion. Siblings---as annoying as they are---when they bond, are bonded together by love. So it basically comes down to whether or not sibling love is a biological emotion, or a sociological construct." He drummed his fingers across his desk. "If it is biological, then it's at odds with sibling competition. If it's not, then it's an imposed value that's overcoming a biological one. Which is just as interesting."

Both twins blinked; the prep, who was visiting the class for the first time, scowled in a desperate attempt at comprehension.

Julian, who had less experience with jargon and somewhat understood their puzzlement, quickly interjected in an attempt to dispel the conversation's heavyhandedness. "Uh, what he means is, do I love Armand because I was born to, or because he's just so darn loveable? And if it's because I have to, then why does nature tell me to fight him as well? And if it's not, is he so loveable that it transcends biology?" The tireless grin reappeared on his face. "Well, of course he's loveable, I mean, look at him, like a big teddybear linebacker---" he broke off when he saw his brother's face.

Armand's eye was twitching. "Sibling love must be biological, because I have no idea why I love you. Shut up."

"Gotcha," Julian yipped, and did.

"Anyway," Armand continued wearily, "This is not a question we can answer in one class period. There's biological evidence in animals for both sibling cooperation and sibling rivalry. In some species---humans included, there are even both simultaneously."

Julian was fidgeting. Armand sighed. "Already?" he drawled. Julian fixed him with a doe-eyed placating look. "Oh all right," his brother consented. "Make it quick."

"Ah, just a quick tidbit of information on the synchronous behaviors," he said hurriedly. "There's actually a scientist who did a study on this---name of William Hamilton---who said that siblings only compete when the benefits are greater than twice the costs of doing so. Because siblings share half their genes. ((1))" He glanced at Armand. "I know that it's obviously too simple a model to apply to human sibling relationships, what with our morals and individual consciousness, but it's something to think about. Ok, I'm done." He lowered his head like a guilty puppy. Half the class cooed; the other half shot nasty looks at Armand, who simply rubbed his temples and sighed.

"Continuing," the elder professor resumed, "As we've said, both cooperation and competition are practiced among humans. Both appear to have some biological basis. Is that basis the prime motivation for the behavior? In other words, is love biological? Who knows."

The prep twin nodded sagely. "That sounds like a wrap-up to me. We're out of time, aren't we?"

Armand nodded gratefully. "We can continue tomorrow on whether or not love is indeed biological." He gazed around the room. "Despite my brother's idiocy---"

"---I take issue with that!"

"---this was a good discussion. I'll see you all tomorrow. Class dismissed!"



Works Cited

1)Sibling Competition Holy snickers, this article is AMAZING. Read it. The first half, anyway.

2)Suckling pigs and sibling competition More math than I ever needed to see on the subject of nipples.

3)Sibling Rivalry What it says.

4)Siblicide Seabirds and other animals killing off their brothers and sisters. Fun stuff, eh?

5)Sibling rivalry in humans On the psychological causes and lifelong effects of human sibling rivalry.

6)Sibling rivalry and begging behaviors Again, just what it sounds like.

** up on your fairy tales, children...

7)Hansel and Gretel!


9)Beauty and the Beast!


(...for the record, I didn't use any of these sources in writing the report. We all know the stories. These links are just here for your enjoyment... and in particular, with the last two, a good laugh at the amount of annotations...)

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