It is an August afternoon in northern India. Though the heat is as thick as a glass of mango lassi, millions of men and women don saris and dhotis to commemorate their love, loyalty and enduring bonds. On this day, women show affection by tying a string around a man’s wrist and placing a sweet on his tongue. In turn, men offer small sums of money—or big cheques for bigger gestures. But this is no wedding or Valentine occasion. It’s Raksha Bandhan , the only brother-sister festival in the world.

I’ve watched my brother, Will, disco in tattered pyjamas. I’ve heard him do every kind of accent (they all sound Mexican). I know it takes him twenty minutes to clean a dirty pot, otherwise calculated as the exact time it takes for me to finish our entire family’s dinner dishes. But now that we are adults, I only see him every few months. He often forgets to call. If there were a North American holiday marking brother-sister kinship, his wife would end up choosing my gift.

Raksha means protection and bandhan a bond. In India, brothers were once seen as caretakers for their sisters, even after the sisters left to live with their husbands. Traditions evolve and times change—women have made significant steps toward independence in Indian society—yet Indian brothers and sisters around the world are still perfectly comfortable expressing deep attachment for their sibs. It is expected of them. “When I try to explain what I would do for my siblings, a lot of my friends don’t understand,” says Torontonian Navdeep Sangha. “My mom, when she goes to India, can show up on her brother’s doorstep and stay for six months. For him to say no is just out of the question. The bonds are really, really strong.”

Remember the media frenzy about Angelina Jolie’s Oscar smooch with her brother James? Or V. C. Andrews’s Flowers in the Attic , the dark page-turner about sibs playing too nice? It kept me a few feet apart from Will during the 1980s. Victorian novels substitute sisterly love for heroines’ more carnal desires. And Greek myth is rife with brothers and sisters angering the gods with their taboo passions. In the West, we have our own one-line cultural script for brother-sister relations. It goes like this: Don’t touch your sister.

The sexual revolution in Europe and North America reinforced this separation. Liberated sisters can open their own doors, thank you. Both brothers and sisters can cry if they feel like it. But duty was cut from the script along with prefab gender roles and replaced with polite distance. As equals, there are no rules requiring brothers and sisters to stick together. Just strict orders to keep apart—or compete.

On an old tape, circa 1974, my brother performs a daycare medley. All you can hear is me gurgling and cooing in the background. I’m only a few months old and already he can’t get a word in. Psychologists would consider this part of the classic struggle for love, approval and family resources. I’m the star! I win! Good for me, but without conventional guidelines, what can we expect of each other beyond simple rivalry?

A great deal, apparently. A recent rash of books on birth order and peer groups—including such bestsellers as Pecking Order: Which Siblings Succeed and Why , The Accidental Bond: The Power of Sibling Relationships , The Sibling Bond and The Birth Order Book: Why You Are the Way You Are —suggest that siblings are key socializing agents. How we act with farting brothers and flirting sisters is a kind of preview for our future marriages and friendships; our siblings teach us how to argue, negotiate and develop intimacy. Some psychologists think we learn these lessons so well that the best marriages mimic siblings’ gender and birth order.

My older brother married a woman who is a younger sister. Dancing with him at his wedding, I felt both proud and sad. As a kid, my brother was all smelly toes and remote-control dictator. But our squabbles taught me how to stand up for myself. Even if he didn’t watch out for me, watching him survive bad hair and bad dates made my transition into adulthood a little easier. I love him no less than any Indian sister would. Now that he has his own family, though, I am not sure what our next steps will be.

In the West, we tend to celebrate relationships that perpetuate the species. We enshrine rituals of courtship, marriage and parenthood. Siblings are secondary. But even if we hate them, siblings are like shadows. We can’t shake them no matter how fast we walk away. Not just a patriarchal ritual, Raksha Bandhan has a lot to teach us. It forces us to consider whether brother-sister ties are Hallmark-worthy.

In a land where Christmas lasts three months, we rightly fear the commercialization of our subtler feelings. Raksha Bandhan ranks second behind Christmas for Indian toy sellers. It is the inspiration for hundreds of East Asian e-cards and online bulletin boards. Even the simple string bracelets that sisters tie on their brothers, called rakhi , have given way to gold, diamond and precious Harry Potter designs.

But surely we need some kind of sibling revelry. Perhaps we can follow the more modest example of Vancouver-area student Yash Kapoor. He and his big sister celebrate their love in a short but significant get-together. “Personally, those few minutes I spend with my sister are precious because it’s just me and her,” he says. “It’s a time when I can show her I really, really care for her.”Then again, my brother has a lot of making up to do. True to form, he didn’t manage to get his comments on siblings to me in time for this article. August should be a good month.